0.70.0

* Fix nth attr merge order to respect precedence hierarchy

nth attrs were merged ON TOP of current-fg/selected-fg attrs, so
nth:regular would clear attrs like underline from current-fg. Fix the
merge chain to apply nth BEFORE the line-type overlay:

  fg < nth < selected-fg < current-fg < hl < selected-hl < current-hl

Store raw current-fg and selected-fg attrs in ColorTheme before they
get merged with fg/ListFg, then pass them as nthOverlay through
printHighlighted to colorOffsets where the correct merge chain is
computed: fgAttr.Merge(nthAttr).Merge(nthOverlay).

Fix #4687

* Make current-fg inherit from list-fg instead of fg

current-fg was inheriting from fg, not list-fg, so setting list-fg
had no effect on the current line. e.g.

  fzf --color fg:dim,list-fg:underline,nth:regular -d / --nth -1

The non-nth part of the current line was dim (from fg) instead of
underline (from list-fg). Resolve ListFg/ListBg earlier in InitTheme
so Current can inherit from them.

* Make selected-fg inherit from list-fg via merge instead of override

selected-fg used o() which replaces the attr from list-fg entirely.
e.g. with fg:dim,selected-fg:italic, the dim was lost on selected
lines because o() replaced dim with italic instead of merging them.
Use ColorAttr.Merge() so attrs are combined additively, consistent
with how current-fg inherits from list-fg.

* Apply selected-fg attrs on current line when item is selected

When an item is both current and selected, the current-line rendering
ignored selected-fg attrs entirely. e.g.

  echo foo | fzf --color fg:dim,nth:regular,current-fg:underline,selected-fg:italic --bind result:select --multi

The italic from selected-fg was lost. Merge NthSelectedAttr into the
overlay and rebuild colBase attr with the correct precedence chain:
fg < selected-fg < current-fg.

.github/labeler.yml

@@ -0,0 +1,64 @@
+go:
+  - changed-files:
+      - any-glob-to-any-file:
+          - src/**
+          - main.go
+          - go.mod
+          - go.sum
+
+shell:
+  - changed-files:
+      - any-glob-to-any-file:
+          - shell/**
+
+bash:
+  - changed-files:
+      - any-glob-to-any-file:
+          - shell/**/*.bash
+
+zsh:
+  - changed-files:
+      - any-glob-to-any-file:
+          - shell/**/*.zsh
+
+fish:
+  - changed-files:
+      - any-glob-to-any-file:
+          - shell/**/*.fish
+
+vim:
+  - changed-files:
+      - any-glob-to-any-file:
+          - plugin/**
+
+docs:
+  - changed-files:
+      - any-glob-to-any-file:
+          - '*.md'
+          - doc/**
+          - man/**
+
+ci:
+  - changed-files:
+      - any-glob-to-any-file:
+          - .github/**
+
+build:
+  - changed-files:
+      - any-glob-to-any-file:
+          - Makefile
+          - .goreleaser.yml
+          - Dockerfile
+
+test:
+  - changed-files:
+      - any-glob-to-any-file:
+          - test/**
+          - src/**/*_test.go
+
+install:
+  - changed-files:
+      - any-glob-to-any-file:
+          - install
+          - install.ps1
+          - uninstall

.github/workflows/labeler.yml

@@ -0,0 +1,17 @@
+name: Label PRs
+
+on:
+  pull_request_target:
+    types: [opened, synchronize, reopened]
+
+permissions:
+  contents: read
+  pull-requests: write
+
+jobs:
+  label:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/labeler@v5
+        with:
+          configuration-path: .github/labeler.yml

.github/workflows/linux.yml

@@ -44,5 +44,10 @@ jobs:
     - name: Unit test
       run: make test
 
+    - name: Fuzz test
+      run: |
+        go test ./src/algo/ -fuzz=FuzzIndexByteTwo -fuzztime=5s
+        go test ./src/algo/ -fuzz=FuzzLastIndexByteTwo -fuzztime=5s
+
     - name: Integration test
       run: make install && ./install --all && tmux new-session -d && ruby test/runner.rb --verbose

CHANGELOG.md

@@ -1,6 +1,41 @@
 CHANGELOG
 =========
 
+0.70.0
+------
+- Added `change-with-nth` action for dynamically changing the `--with-nth` option.
+    - Requires `--with-nth` to be set initially.
+    - Multiple options separated by `|` can be given to cycle through.
+  ```sh
+  echo -e "a b c\nd e f\ng h i" | fzf --with-nth .. \
+    --bind 'space:change-with-nth(1|2|3|1,3|2,3|)'
+  ```
+- Added `change-header-lines` action for dynamically changing the `--header-lines` option
+- Performance improvements (1.3x to 1.9x faster filtering depending on query)
+  ```
+  === query: 'l' ===
+    [all]   baseline:   168.87ms  current:    95.21ms  (1.77x)  matches: 5069891 (94.78%)
+    [1T]    baseline:  1652.22ms  current:   841.40ms  (1.96x)  matches: 5069891 (94.78%)
+
+  === query: 'lin' ===
+    [all]   baseline:   343.27ms  current:   252.59ms  (1.36x)  matches: 3516507 (65.74%)
+    [1T]    baseline:  3199.89ms  current:  2230.64ms  (1.43x)  matches: 3516507 (65.74%)
+
+  === query: 'linux' ===
+    [all]   baseline:    85.47ms  current:    63.72ms  (1.34x)  matches: 307229 (5.74%)
+    [1T]    baseline:   774.64ms  current:   589.32ms  (1.31x)  matches: 307229 (5.74%)
+
+  === query: 'linuxlinux' ===
+    [all]   baseline:    55.13ms  current:    35.67ms  (1.55x)  matches: 12230 (0.23%)
+    [1T]    baseline:   461.99ms  current:   332.38ms  (1.39x)  matches: 12230 (0.23%)
+
+  === query: 'linuxlinuxlinux' ===
+    [all]   baseline:    51.77ms  current:    32.53ms  (1.59x)  matches: 865 (0.02%)
+    [1T]    baseline:   409.99ms  current:   296.33ms  (1.38x)  matches: 865 (0.02%)
+  ```
+- Fixed `nth` attribute merge order to respect precedence hierarchy (#4697)
+- bash: Replaced `printf` with builtin `printf` to bypass local indirections (#4684) (@DarrenBishop)
+
 0.68.0
 ------
 - Implemented word wrapping in the list section

install

@@ -2,7 +2,7 @@
 
 set -u
 
-version=0.68.0
+version=0.70.0
 auto_completion=
 key_bindings=
 update_config=2

install.ps1

@@ -1,4 +1,4 @@
-$version="0.68.0"
+$version="0.70.0"
 
 $fzf_base=Split-Path -Parent $MyInvocation.MyCommand.Definition
 

main.go

@@ -11,7 +11,7 @@ import (
 	"github.com/junegunn/fzf/src/protector"
 )
 
-var version = "0.68"
+var version = "0.70"
 var revision = "devel"
 
 //go:embed shell/key-bindings.bash

man/man1/fzf-tmux.1

@@ -21,7 +21,7 @@ LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 THE SOFTWARE.
 ..
-.TH fzf\-tmux 1 "Feb 2026" "fzf 0.68.0" "fzf\-tmux - open fzf in tmux split pane"
+.TH fzf\-tmux 1 "Mar 2026" "fzf 0.70.0" "fzf\-tmux - open fzf in tmux split pane"
 
 .SH NAME
 fzf\-tmux - open fzf in tmux split pane

man/man1/fzf.1

@@ -21,7 +21,7 @@ LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 THE SOFTWARE.
 ..
-.TH fzf 1 "Feb 2026" "fzf 0.68.0" "fzf - a command-line fuzzy finder"
+.TH fzf 1 "Mar 2026" "fzf 0.70.0" "fzf - a command-line fuzzy finder"
 
 .SH NAME
 fzf - a command-line fuzzy finder
@@ -134,6 +134,14 @@ e.g.
      # Use template to rearrange fields
      echo foo,bar,baz | fzf --delimiter , --with-nth '{n},{1},{3},{2},{1..2}'
 .RE
+.RS
+
+\fBchange\-with\-nth\fR action is only available when \fB\-\-with\-nth\fR is set.
+When \fB\-\-with\-nth\fR is used, fzf retains the original input lines in memory
+so they can be re\-transformed on the fly (e.g. \fB\-\-with\-nth ..\fR to keep
+the original presentation). This increases memory usage, so only use
+\fB\-\-with\-nth\fR when you actually need field transformation.
+.RE
 .TP
 .BI "\-\-accept\-nth=" "N[,..] or TEMPLATE"
 Define which fields to print on accept. The last delimiter is stripped from the
@@ -1229,6 +1237,18 @@ Here is an example script that uses a Unix socket instead of a TCP port.
     curl --unix-socket /tmp/fzf.sock http -d up
     \fR
 
+.TP
+.BI "\-\-threads=" "N"
+Number of matcher threads to use. The default value is
+\fBmin(8 * NUM_CPU, 32)\fR.
+.TP
+.BI "\-\-bench=" "DURATION"
+Repeatedly run \fB\-\-filter\fR for the given duration and print timing
+statistics. Must be used with \fB\-\-filter\fR.
+
+e.g.
+     \fBcat /usr/share/dict/words | fzf \-\-filter abc \-\-bench 10s\fR
+
 .SS DIRECTORY TRAVERSAL
 .TP
 .B "\-\-walker=[file][,dir][,follow][,hidden]"
@@ -1398,6 +1418,8 @@ fzf exports the following environment variables to its child processes.
 .br
 .BR FZF_NTH "             Current \-\-nth option"
 .br
+.BR FZF_WITH_NTH "        Current \-\-with\-nth option"
+.br
 .BR FZF_PROMPT "          Prompt string"
 .br
 .BR FZF_GHOST "           Ghost string"
@@ -1881,12 +1903,14 @@ A key or an event can be bound to one or more of the following actions.
     \fBchange\-border\-label(...)\fR     (change \fB\-\-border\-label\fR to the given string)
     \fBchange\-ghost(...)\fR            (change ghost text to the given string)
     \fBchange\-header(...)\fR           (change header to the given string; doesn't affect \fB\-\-header\-lines\fR)
+    \fBchange\-header\-lines(N)\fR       (change the number of \fB\-\-header\-lines\fR)
     \fBchange\-header\-label(...)\fR     (change \fB\-\-header\-label\fR to the given string)
     \fBchange\-input\-label(...)\fR      (change \fB\-\-input\-label\fR to the given string)
     \fBchange\-list\-label(...)\fR       (change \fB\-\-list\-label\fR to the given string)
     \fBchange\-multi\fR                 (enable multi-select mode with no limit)
     \fBchange\-multi(...)\fR            (enable multi-select mode with a limit or disable it with 0)
     \fBchange\-nth(...)\fR              (change \fB\-\-nth\fR option; rotate through the multiple options separated by '|')
+    \fBchange\-with\-nth(...)\fR         (change \fB\-\-with\-nth\fR option; rotate through the multiple options separated by '|')
     \fBchange\-pointer(...)\fR          (change \fB\-\-pointer\fR option)
     \fBchange\-preview(...)\fR          (change \fB\-\-preview\fR option)
     \fBchange\-preview\-label(...)\fR    (change \fB\-\-preview\-label\fR to the given string)
@@ -1987,10 +2011,12 @@ A key or an event can be bound to one or more of the following actions.
     \fBtransform\-border\-label(...)\fR  (transform border label using an external command)
     \fBtransform\-ghost(...)\fR         (transform ghost text using an external command)
     \fBtransform\-header(...)\fR        (transform header using an external command)
+    \fBtransform\-header\-lines(...)\fR  (transform the number of \fB\-\-header\-lines\fR using an external command)
     \fBtransform\-header\-label(...)\fR  (transform header label using an external command)
     \fBtransform\-input\-label(...)\fR   (transform input label using an external command)
     \fBtransform\-list\-label(...)\fR    (transform list label using an external command)
     \fBtransform\-nth(...)\fR           (transform nth using an external command)
+    \fBtransform\-with\-nth(...)\fR      (transform with-nth using an external command)
     \fBtransform\-pointer(...)\fR       (transform pointer using an external command)
     \fBtransform\-preview\-label(...)\fR (transform preview label using an external command)
     \fBtransform\-prompt(...)\fR        (transform prompt string using an external command)

shell/completion.bash

@@ -38,9 +38,9 @@ if [[ $- =~ i ]]; then
 # the changes. See code comments in "common.sh" for the implementation details.
 
 __fzf_defaults() {
-  printf '%s\n' "--height ${FZF_TMUX_HEIGHT:-40%} --min-height 20+ --bind=ctrl-z:ignore $1"
+  builtin printf '%s\n' "--height ${FZF_TMUX_HEIGHT:-40%} --min-height 20+ --bind=ctrl-z:ignore $1"
   command cat "${FZF_DEFAULT_OPTS_FILE-}" 2> /dev/null
-  printf '%s\n' "${FZF_DEFAULT_OPTS-} $2"
+  builtin printf '%s\n' "${FZF_DEFAULT_OPTS-} $2"
 }
 
 __fzf_exec_awk() {
@@ -81,7 +81,7 @@ __fzf_orig_completion() {
       f="${BASH_REMATCH[2]}"
       cmd="${BASH_REMATCH[3]}"
       [[ $f == _fzf_* ]] && continue
-      printf -v "_fzf_orig_completion_${cmd//[^A-Za-z0-9_]/_}" "%s" "${comp} %s ${cmd} #${f}"
+      builtin printf -v "_fzf_orig_completion_${cmd//[^A-Za-z0-9_]/_}" "%s" "${comp} %s ${cmd} #${f}"
       if [[ $l == *" -o nospace "* ]] && [[ ${__fzf_nospace_commands-} != *" $cmd "* ]]; then
         __fzf_nospace_commands="${__fzf_nospace_commands-} $cmd "
       fi
@@ -111,7 +111,7 @@ __fzf_orig_completion_instantiate() {
   orig="${!orig_var-}"
   orig="${orig%#*}"
   [[ $orig == *' %s '* ]] || return 1
-  printf -v REPLY "$orig" "$func"
+  builtin printf -v REPLY "$orig" "$func"
 }
 
 _fzf_opts_completion() {
@@ -376,7 +376,7 @@ __fzf_generic_path_completion() {
             eval "rest=(${FZF_COMPLETION_PATH_OPTS-})"
           fi
           if declare -F "$1" > /dev/null; then
-            eval "$1 $(printf %q "$dir")" | __fzf_comprun "$4" -q "$leftover" "${rest[@]}"
+            eval "$1 $(builtin printf %q "$dir")" | __fzf_comprun "$4" -q "$leftover" "${rest[@]}"
           else
             if [[ $1 =~ dir ]]; then
               walker=dir,follow
@@ -385,7 +385,7 @@ __fzf_generic_path_completion() {
             fi
             __fzf_comprun "$4" -q "$leftover" --walker "$walker" --walker-root="$dir" "${rest[@]}"
           fi | while read -r item; do
-            printf "%q " "${item%$3}$3"
+            builtin printf "%q " "${item%$3}$3"
           done
         )
         matches=${matches% }
@@ -395,9 +395,9 @@ __fzf_generic_path_completion() {
         else
           COMPREPLY=("$cur")
         fi
-        # To redraw line after fzf closes (printf '\e[5n')
+        # To redraw line after fzf closes (builtin printf '\e[5n')
         bind '"\e[0n": redraw-current-line' 2> /dev/null
-        printf '\e[5n'
+        builtin printf '\e[5n'
         return 0
       fi
       dir=$(command dirname "$dir")
@@ -455,7 +455,7 @@ _fzf_complete() {
       COMPREPLY=("$cur")
     fi
     bind '"\e[0n": redraw-current-line' 2> /dev/null
-    printf '\e[5n'
+    builtin printf '\e[5n'
     return 0
   else
     _fzf_handle_dynamic_completion "$cmd" "${rest[@]}"
@@ -527,7 +527,7 @@ _fzf_proc_completion_post() {
 #     # Set the local attribute for any non-local variable that is set by _known_hosts_real()
 #     local COMPREPLY=()
 #     _known_hosts_real ''
-#     printf '%s\n' "${COMPREPLY[@]}" | command sort -u --version-sort
+#     builtin printf '%s\n' "${COMPREPLY[@]}" | command sort -u --version-sort
 #   }
 if ! declare -F __fzf_list_hosts > /dev/null; then
   __fzf_list_hosts() {

src/actiontype_string.go

@@ -30,161 +30,167 @@ func _() {
 	_ = x[actChangeBorderLabel-19]
 	_ = x[actChangeGhost-20]
 	_ = x[actChangeHeader-21]
-	_ = x[actChangeFooter-22]
+	_ = x[actChangeHeaderLines-22]
-	_ = x[actChangeHeaderLabel-23]
+	_ = x[actChangeFooter-23]
-	_ = x[actChangeFooterLabel-24]
+	_ = x[actChangeHeaderLabel-24]
-	_ = x[actChangeInputLabel-25]
+	_ = x[actChangeFooterLabel-25]
-	_ = x[actChangeListLabel-26]
+	_ = x[actChangeInputLabel-26]
-	_ = x[actChangeMulti-27]
+	_ = x[actChangeListLabel-27]
-	_ = x[actChangeNth-28]
+	_ = x[actChangeMulti-28]
-	_ = x[actChangePointer-29]
+	_ = x[actChangeNth-29]
-	_ = x[actChangePreview-30]
+	_ = x[actChangeWithNth-30]
-	_ = x[actChangePreviewLabel-31]
+	_ = x[actChangePointer-31]
-	_ = x[actChangePreviewWindow-32]
+	_ = x[actChangePreview-32]
-	_ = x[actChangePrompt-33]
+	_ = x[actChangePreviewLabel-33]
-	_ = x[actChangeQuery-34]
+	_ = x[actChangePreviewWindow-34]
-	_ = x[actClearScreen-35]
+	_ = x[actChangePrompt-35]
-	_ = x[actClearQuery-36]
+	_ = x[actChangeQuery-36]
-	_ = x[actClearSelection-37]
+	_ = x[actClearScreen-37]
-	_ = x[actClose-38]
+	_ = x[actClearQuery-38]
-	_ = x[actDeleteChar-39]
+	_ = x[actClearSelection-39]
-	_ = x[actDeleteCharEof-40]
+	_ = x[actClose-40]
-	_ = x[actEndOfLine-41]
+	_ = x[actDeleteChar-41]
-	_ = x[actFatal-42]
+	_ = x[actDeleteCharEof-42]
-	_ = x[actForwardChar-43]
+	_ = x[actEndOfLine-43]
-	_ = x[actForwardWord-44]
+	_ = x[actFatal-44]
-	_ = x[actForwardSubWord-45]
+	_ = x[actForwardChar-45]
-	_ = x[actKillLine-46]
+	_ = x[actForwardWord-46]
-	_ = x[actKillWord-47]
+	_ = x[actForwardSubWord-47]
-	_ = x[actKillSubWord-48]
+	_ = x[actKillLine-48]
-	_ = x[actUnixLineDiscard-49]
+	_ = x[actKillWord-49]
-	_ = x[actUnixWordRubout-50]
+	_ = x[actKillSubWord-50]
-	_ = x[actYank-51]
+	_ = x[actUnixLineDiscard-51]
-	_ = x[actBackwardKillWord-52]
+	_ = x[actUnixWordRubout-52]
-	_ = x[actBackwardKillSubWord-53]
+	_ = x[actYank-53]
-	_ = x[actSelectAll-54]
+	_ = x[actBackwardKillWord-54]
-	_ = x[actDeselectAll-55]
+	_ = x[actBackwardKillSubWord-55]
-	_ = x[actToggle-56]
+	_ = x[actSelectAll-56]
-	_ = x[actToggleSearch-57]
+	_ = x[actDeselectAll-57]
-	_ = x[actToggleAll-58]
+	_ = x[actToggle-58]
-	_ = x[actToggleDown-59]
+	_ = x[actToggleSearch-59]
-	_ = x[actToggleUp-60]
+	_ = x[actToggleAll-60]
-	_ = x[actToggleIn-61]
+	_ = x[actToggleDown-61]
-	_ = x[actToggleOut-62]
+	_ = x[actToggleUp-62]
-	_ = x[actToggleTrack-63]
+	_ = x[actToggleIn-63]
-	_ = x[actToggleTrackCurrent-64]
+	_ = x[actToggleOut-64]
-	_ = x[actToggleHeader-65]
+	_ = x[actToggleTrack-65]
-	_ = x[actToggleWrap-66]
+	_ = x[actToggleTrackCurrent-66]
-	_ = x[actToggleWrapWord-67]
+	_ = x[actToggleHeader-67]
-	_ = x[actToggleMultiLine-68]
+	_ = x[actToggleWrap-68]
-	_ = x[actToggleHscroll-69]
+	_ = x[actToggleWrapWord-69]
-	_ = x[actToggleRaw-70]
+	_ = x[actToggleMultiLine-70]
-	_ = x[actEnableRaw-71]
+	_ = x[actToggleHscroll-71]
-	_ = x[actDisableRaw-72]
+	_ = x[actToggleRaw-72]
-	_ = x[actTrackCurrent-73]
+	_ = x[actEnableRaw-73]
-	_ = x[actToggleInput-74]
+	_ = x[actDisableRaw-74]
-	_ = x[actHideInput-75]
+	_ = x[actTrackCurrent-75]
-	_ = x[actShowInput-76]
+	_ = x[actToggleInput-76]
-	_ = x[actUntrackCurrent-77]
+	_ = x[actHideInput-77]
-	_ = x[actDown-78]
+	_ = x[actShowInput-78]
-	_ = x[actDownMatch-79]
+	_ = x[actUntrackCurrent-79]
-	_ = x[actUp-80]
+	_ = x[actDown-80]
-	_ = x[actUpMatch-81]
+	_ = x[actDownMatch-81]
-	_ = x[actPageUp-82]
+	_ = x[actUp-82]
-	_ = x[actPageDown-83]
+	_ = x[actUpMatch-83]
-	_ = x[actPosition-84]
+	_ = x[actPageUp-84]
-	_ = x[actHalfPageUp-85]
+	_ = x[actPageDown-85]
-	_ = x[actHalfPageDown-86]
+	_ = x[actPosition-86]
-	_ = x[actOffsetUp-87]
+	_ = x[actHalfPageUp-87]
-	_ = x[actOffsetDown-88]
+	_ = x[actHalfPageDown-88]
-	_ = x[actOffsetMiddle-89]
+	_ = x[actOffsetUp-89]
-	_ = x[actJump-90]
+	_ = x[actOffsetDown-90]
-	_ = x[actJumpAccept-91]
+	_ = x[actOffsetMiddle-91]
-	_ = x[actPrintQuery-92]
+	_ = x[actJump-92]
-	_ = x[actRefreshPreview-93]
+	_ = x[actJumpAccept-93]
-	_ = x[actReplaceQuery-94]
+	_ = x[actPrintQuery-94]
-	_ = x[actToggleSort-95]
+	_ = x[actRefreshPreview-95]
-	_ = x[actShowPreview-96]
+	_ = x[actReplaceQuery-96]
-	_ = x[actHidePreview-97]
+	_ = x[actToggleSort-97]
-	_ = x[actTogglePreview-98]
+	_ = x[actShowPreview-98]
-	_ = x[actTogglePreviewWrap-99]
+	_ = x[actHidePreview-99]
-	_ = x[actTogglePreviewWrapWord-100]
+	_ = x[actTogglePreview-100]
-	_ = x[actTransform-101]
+	_ = x[actTogglePreviewWrap-101]
-	_ = x[actTransformBorderLabel-102]
+	_ = x[actTogglePreviewWrapWord-102]
-	_ = x[actTransformGhost-103]
+	_ = x[actTransform-103]
-	_ = x[actTransformHeader-104]
+	_ = x[actTransformBorderLabel-104]
-	_ = x[actTransformFooter-105]
+	_ = x[actTransformGhost-105]
-	_ = x[actTransformHeaderLabel-106]
+	_ = x[actTransformHeader-106]
-	_ = x[actTransformFooterLabel-107]
+	_ = x[actTransformHeaderLines-107]
-	_ = x[actTransformInputLabel-108]
+	_ = x[actTransformFooter-108]
-	_ = x[actTransformListLabel-109]
+	_ = x[actTransformHeaderLabel-109]
-	_ = x[actTransformNth-110]
+	_ = x[actTransformFooterLabel-110]
-	_ = x[actTransformPointer-111]
+	_ = x[actTransformInputLabel-111]
-	_ = x[actTransformPreviewLabel-112]
+	_ = x[actTransformListLabel-112]
-	_ = x[actTransformPrompt-113]
+	_ = x[actTransformNth-113]
-	_ = x[actTransformQuery-114]
+	_ = x[actTransformWithNth-114]
-	_ = x[actTransformSearch-115]
+	_ = x[actTransformPointer-115]
-	_ = x[actTrigger-116]
+	_ = x[actTransformPreviewLabel-116]
-	_ = x[actBgTransform-117]
+	_ = x[actTransformPrompt-117]
-	_ = x[actBgTransformBorderLabel-118]
+	_ = x[actTransformQuery-118]
-	_ = x[actBgTransformGhost-119]
+	_ = x[actTransformSearch-119]
-	_ = x[actBgTransformHeader-120]
+	_ = x[actTrigger-120]
-	_ = x[actBgTransformFooter-121]
+	_ = x[actBgTransform-121]
-	_ = x[actBgTransformHeaderLabel-122]
+	_ = x[actBgTransformBorderLabel-122]
-	_ = x[actBgTransformFooterLabel-123]
+	_ = x[actBgTransformGhost-123]
-	_ = x[actBgTransformInputLabel-124]
+	_ = x[actBgTransformHeader-124]
-	_ = x[actBgTransformListLabel-125]
+	_ = x[actBgTransformHeaderLines-125]
-	_ = x[actBgTransformNth-126]
+	_ = x[actBgTransformFooter-126]
-	_ = x[actBgTransformPointer-127]
+	_ = x[actBgTransformHeaderLabel-127]
-	_ = x[actBgTransformPreviewLabel-128]
+	_ = x[actBgTransformFooterLabel-128]
-	_ = x[actBgTransformPrompt-129]
+	_ = x[actBgTransformInputLabel-129]
-	_ = x[actBgTransformQuery-130]
+	_ = x[actBgTransformListLabel-130]
-	_ = x[actBgTransformSearch-131]
+	_ = x[actBgTransformNth-131]
-	_ = x[actBgCancel-132]
+	_ = x[actBgTransformWithNth-132]
-	_ = x[actSearch-133]
+	_ = x[actBgTransformPointer-133]
-	_ = x[actPreview-134]
+	_ = x[actBgTransformPreviewLabel-134]
-	_ = x[actPreviewTop-135]
+	_ = x[actBgTransformPrompt-135]
-	_ = x[actPreviewBottom-136]
+	_ = x[actBgTransformQuery-136]
-	_ = x[actPreviewUp-137]
+	_ = x[actBgTransformSearch-137]
-	_ = x[actPreviewDown-138]
+	_ = x[actBgCancel-138]
-	_ = x[actPreviewPageUp-139]
+	_ = x[actSearch-139]
-	_ = x[actPreviewPageDown-140]
+	_ = x[actPreview-140]
-	_ = x[actPreviewHalfPageUp-141]
+	_ = x[actPreviewTop-141]
-	_ = x[actPreviewHalfPageDown-142]
+	_ = x[actPreviewBottom-142]
-	_ = x[actPrevHistory-143]
+	_ = x[actPreviewUp-143]
-	_ = x[actPrevSelected-144]
+	_ = x[actPreviewDown-144]
-	_ = x[actPrint-145]
+	_ = x[actPreviewPageUp-145]
-	_ = x[actPut-146]
+	_ = x[actPreviewPageDown-146]
-	_ = x[actNextHistory-147]
+	_ = x[actPreviewHalfPageUp-147]
-	_ = x[actNextSelected-148]
+	_ = x[actPreviewHalfPageDown-148]
-	_ = x[actExecute-149]
+	_ = x[actPrevHistory-149]
-	_ = x[actExecuteSilent-150]
+	_ = x[actPrevSelected-150]
-	_ = x[actExecuteMulti-151]
+	_ = x[actPrint-151]
-	_ = x[actSigStop-152]
+	_ = x[actPut-152]
-	_ = x[actBest-153]
+	_ = x[actNextHistory-153]
-	_ = x[actFirst-154]
+	_ = x[actNextSelected-154]
-	_ = x[actLast-155]
+	_ = x[actExecute-155]
-	_ = x[actReload-156]
+	_ = x[actExecuteSilent-156]
-	_ = x[actReloadSync-157]
+	_ = x[actExecuteMulti-157]
-	_ = x[actDisableSearch-158]
+	_ = x[actSigStop-158]
-	_ = x[actEnableSearch-159]
+	_ = x[actBest-159]
-	_ = x[actSelect-160]
+	_ = x[actFirst-160]
-	_ = x[actDeselect-161]
+	_ = x[actLast-161]
-	_ = x[actUnbind-162]
+	_ = x[actReload-162]
-	_ = x[actRebind-163]
+	_ = x[actReloadSync-163]
-	_ = x[actToggleBind-164]
+	_ = x[actDisableSearch-164]
-	_ = x[actBecome-165]
+	_ = x[actEnableSearch-165]
-	_ = x[actShowHeader-166]
+	_ = x[actSelect-166]
-	_ = x[actHideHeader-167]
+	_ = x[actDeselect-167]
-	_ = x[actBell-168]
+	_ = x[actUnbind-168]
-	_ = x[actExclude-169]
+	_ = x[actRebind-169]
-	_ = x[actExcludeMulti-170]
+	_ = x[actToggleBind-170]
-	_ = x[actAsync-171]
+	_ = x[actBecome-171]
+	_ = x[actShowHeader-172]
+	_ = x[actHideHeader-173]
+	_ = x[actBell-174]
+	_ = x[actExclude-175]
+	_ = x[actExcludeMulti-176]
+	_ = x[actAsync-177]
 }
 
-const _actionType_name = "actIgnoreactStartactClickactInvalidactBracketedPasteBeginactBracketedPasteEndactCharactMouseactBeginningOfLineactAbortactAcceptactAcceptNonEmptyactAcceptOrPrintQueryactBackwardCharactBackwardDeleteCharactBackwardDeleteCharEofactBackwardWordactBackwardSubWordactCancelactChangeBorderLabelactChangeGhostactChangeHeaderactChangeFooteractChangeHeaderLabelactChangeFooterLabelactChangeInputLabelactChangeListLabelactChangeMultiactChangeNthactChangePointeractChangePreviewactChangePreviewLabelactChangePreviewWindowactChangePromptactChangeQueryactClearScreenactClearQueryactClearSelectionactCloseactDeleteCharactDeleteCharEofactEndOfLineactFatalactForwardCharactForwardWordactForwardSubWordactKillLineactKillWordactKillSubWordactUnixLineDiscardactUnixWordRuboutactYankactBackwardKillWordactBackwardKillSubWordactSelectAllactDeselectAllactToggleactToggleSearchactToggleAllactToggleDownactToggleUpactToggleInactToggleOutactToggleTrackactToggleTrackCurrentactToggleHeaderactToggleWrapactToggleWrapWordactToggleMultiLineactToggleHscrollactToggleRawactEnableRawactDisableRawactTrackCurrentactToggleInputactHideInputactShowInputactUntrackCurrentactDownactDownMatchactUpactUpMatchactPageUpactPageDownactPositionactHalfPageUpactHalfPageDownactOffsetUpactOffsetDownactOffsetMiddleactJumpactJumpAcceptactPrintQueryactRefreshPreviewactReplaceQueryactToggleSortactShowPreviewactHidePreviewactTogglePreviewactTogglePreviewWrapactTogglePreviewWrapWordactTransformactTransformBorderLabelactTransformGhostactTransformHeaderactTransformFooteractTransformHeaderLabelactTransformFooterLabelactTransformInputLabelactTransformListLabelactTransformNthactTransformPointeractTransformPreviewLabelactTransformPromptactTransformQueryactTransformSearchactTriggeractBgTransformactBgTransformBorderLabelactBgTransformGhostactBgTransformHeaderactBgTransformFooteractBgTransformHeaderLabelactBgTransformFooterLabelactBgTransformInputLabelactBgTransformListLabelactBgTransformNthactBgTransformPointeractBgTransformPreviewLabelactBgTransformPromptactBgTransformQueryactBgTransformSearchactBgCancelactSearchactPreviewactPreviewTopactPreviewBottomactPreviewUpactPreviewDownactPreviewPageUpactPreviewPageDownactPreviewHalfPageUpactPreviewHalfPageDownactPrevHistoryactPrevSelectedactPrintactPutactNextHistoryactNextSelectedactExecuteactExecuteSilentactExecuteMultiactSigStopactBestactFirstactLastactReloadactReloadSyncactDisableSearchactEnableSearchactSelectactDeselectactUnbindactRebindactToggleBindactBecomeactShowHeaderactHideHeaderactBellactExcludeactExcludeMultiactAsync"
+const _actionType_name = "actIgnoreactStartactClickactInvalidactBracketedPasteBeginactBracketedPasteEndactCharactMouseactBeginningOfLineactAbortactAcceptactAcceptNonEmptyactAcceptOrPrintQueryactBackwardCharactBackwardDeleteCharactBackwardDeleteCharEofactBackwardWordactBackwardSubWordactCancelactChangeBorderLabelactChangeGhostactChangeHeaderactChangeHeaderLinesactChangeFooteractChangeHeaderLabelactChangeFooterLabelactChangeInputLabelactChangeListLabelactChangeMultiactChangeNthactChangeWithNthactChangePointeractChangePreviewactChangePreviewLabelactChangePreviewWindowactChangePromptactChangeQueryactClearScreenactClearQueryactClearSelectionactCloseactDeleteCharactDeleteCharEofactEndOfLineactFatalactForwardCharactForwardWordactForwardSubWordactKillLineactKillWordactKillSubWordactUnixLineDiscardactUnixWordRuboutactYankactBackwardKillWordactBackwardKillSubWordactSelectAllactDeselectAllactToggleactToggleSearchactToggleAllactToggleDownactToggleUpactToggleInactToggleOutactToggleTrackactToggleTrackCurrentactToggleHeaderactToggleWrapactToggleWrapWordactToggleMultiLineactToggleHscrollactToggleRawactEnableRawactDisableRawactTrackCurrentactToggleInputactHideInputactShowInputactUntrackCurrentactDownactDownMatchactUpactUpMatchactPageUpactPageDownactPositionactHalfPageUpactHalfPageDownactOffsetUpactOffsetDownactOffsetMiddleactJumpactJumpAcceptactPrintQueryactRefreshPreviewactReplaceQueryactToggleSortactShowPreviewactHidePreviewactTogglePreviewactTogglePreviewWrapactTogglePreviewWrapWordactTransformactTransformBorderLabelactTransformGhostactTransformHeaderactTransformHeaderLinesactTransformFooteractTransformHeaderLabelactTransformFooterLabelactTransformInputLabelactTransformListLabelactTransformNthactTransformWithNthactTransformPointeractTransformPreviewLabelactTransformPromptactTransformQueryactTransformSearchactTriggeractBgTransformactBgTransformBorderLabelactBgTransformGhostactBgTransformHeaderactBgTransformHeaderLinesactBgTransformFooteractBgTransformHeaderLabelactBgTransformFooterLabelactBgTransformInputLabelactBgTransformListLabelactBgTransformNthactBgTransformWithNthactBgTransformPointeractBgTransformPreviewLabelactBgTransformPromptactBgTransformQueryactBgTransformSearchactBgCancelactSearchactPreviewactPreviewTopactPreviewBottomactPreviewUpactPreviewDownactPreviewPageUpactPreviewPageDownactPreviewHalfPageUpactPreviewHalfPageDownactPrevHistoryactPrevSelectedactPrintactPutactNextHistoryactNextSelectedactExecuteactExecuteSilentactExecuteMultiactSigStopactBestactFirstactLastactReloadactReloadSyncactDisableSearchactEnableSearchactSelectactDeselectactUnbindactRebindactToggleBindactBecomeactShowHeaderactHideHeaderactBellactExcludeactExcludeMultiactAsync"
 
-var _actionType_index = [...]uint16{0, 9, 17, 25, 35, 57, 77, 84, 92, 110, 118, 127, 144, 165, 180, 201, 225, 240, 258, 267, 287, 301, 316, 331, 351, 371, 390, 408, 422, 434, 450, 466, 487, 509, 524, 538, 552, 565, 582, 590, 603, 619, 631, 639, 653, 667, 684, 695, 706, 720, 738, 755, 762, 781, 803, 815, 829, 838, 853, 865, 878, 889, 900, 912, 926, 947, 962, 975, 992, 1010, 1026, 1038, 1050, 1063, 1078, 1092, 1104, 1116, 1133, 1140, 1152, 1157, 1167, 1176, 1187, 1198, 1211, 1226, 1237, 1250, 1265, 1272, 1285, 1298, 1315, 1330, 1343, 1357, 1371, 1387, 1407, 1431, 1443, 1466, 1483, 1501, 1519, 1542, 1565, 1587, 1608, 1623, 1642, 1666, 1684, 1701, 1719, 1729, 1743, 1768, 1787, 1807, 1827, 1852, 1877, 1901, 1924, 1941, 1962, 1988, 2008, 2027, 2047, 2058, 2067, 2077, 2090, 2106, 2118, 2132, 2148, 2166, 2186, 2208, 2222, 2237, 2245, 2251, 2265, 2280, 2290, 2306, 2321, 2331, 2338, 2346, 2353, 2362, 2375, 2391, 2406, 2415, 2426, 2435, 2444, 2457, 2466, 2479, 2492, 2499, 2509, 2524, 2532}
+var _actionType_index = [...]uint16{0, 9, 17, 25, 35, 57, 77, 84, 92, 110, 118, 127, 144, 165, 180, 201, 225, 240, 258, 267, 287, 301, 316, 336, 351, 371, 391, 410, 428, 442, 454, 470, 486, 502, 523, 545, 560, 574, 588, 601, 618, 626, 639, 655, 667, 675, 689, 703, 720, 731, 742, 756, 774, 791, 798, 817, 839, 851, 865, 874, 889, 901, 914, 925, 936, 948, 962, 983, 998, 1011, 1028, 1046, 1062, 1074, 1086, 1099, 1114, 1128, 1140, 1152, 1169, 1176, 1188, 1193, 1203, 1212, 1223, 1234, 1247, 1262, 1273, 1286, 1301, 1308, 1321, 1334, 1351, 1366, 1379, 1393, 1407, 1423, 1443, 1467, 1479, 1502, 1519, 1537, 1560, 1578, 1601, 1624, 1646, 1667, 1682, 1701, 1720, 1744, 1762, 1779, 1797, 1807, 1821, 1846, 1865, 1885, 1910, 1930, 1955, 1980, 2004, 2027, 2044, 2065, 2086, 2112, 2132, 2151, 2171, 2182, 2191, 2201, 2214, 2230, 2242, 2256, 2272, 2290, 2310, 2332, 2346, 2361, 2369, 2375, 2389, 2404, 2414, 2430, 2445, 2455, 2462, 2470, 2477, 2486, 2499, 2515, 2530, 2539, 2550, 2559, 2568, 2581, 2590, 2603, 2616, 2623, 2633, 2648, 2656}
 
 func (i actionType) String() string {
 	if i < 0 || i >= actionType(len(_actionType_index)-1) {

src/algo/SIMD.md

@@ -0,0 +1,99 @@
+# SIMD byte search: `indexByteTwo` / `lastIndexByteTwo`
+
+## What these functions do
+
+`indexByteTwo(s []byte, b1, b2 byte) int` — returns the index of the
+**first** occurrence of `b1` or `b2` in `s`, or `-1`.
+
+`lastIndexByteTwo(s []byte, b1, b2 byte) int` — returns the index of the
+**last** occurrence of `b1` or `b2` in `s`, or `-1`.
+
+They are used by the fuzzy matching algorithm (`algo.go`) to skip ahead
+during case-insensitive search. Instead of calling `bytes.IndexByte` twice
+(once for lowercase, once for uppercase), a single SIMD pass finds both at
+once.
+
+## File layout
+
+| File                  | Purpose                                                           |
+| ------                | ---------                                                         |
+| `indexbyte2_arm64.go` | Go declarations (`//go:noescape`) for ARM64                       |
+| `indexbyte2_arm64.s`  | ARM64 NEON assembly (32-byte aligned blocks, syndrome extraction) |
+| `indexbyte2_amd64.go` | Go declarations + AVX2 runtime detection for AMD64                |
+| `indexbyte2_amd64.s`  | AMD64 AVX2/SSE2 assembly with CPUID dispatch                      |
+| `indexbyte2_other.go` | Pure Go fallback for all other architectures                      |
+| `indexbyte2_test.go`  | Unit tests, exhaustive tests, fuzz tests, and benchmarks          |
+
+## How the SIMD implementations work
+
+**ARM64 (NEON):**
+- Broadcasts both needle bytes into NEON registers (`VMOV`).
+- Processes 32-byte aligned chunks. For each chunk, compares all bytes
+  against both needles (`VCMEQ`), ORs the results (`VORR`), and builds a
+  64-bit syndrome with 2 bits per byte.
+- `indexByteTwo` uses `RBIT` + `CLZ` to find the lowest set bit (first match).
+- `lastIndexByteTwo` scans backward and uses `CLZ` on the raw syndrome to
+  find the highest set bit (last match).
+- Handles alignment and partial first/last blocks with bit masking.
+- Adapted from Go's `internal/bytealg/indexbyte_arm64.s`.
+
+**AMD64 (AVX2 with SSE2 fallback):**
+- At init time, `cpuHasAVX2()` checks CPUID + XGETBV for AVX2 and OS YMM
+  support. The result is cached in `_useAVX2`.
+- **AVX2 path** (inputs >= 32 bytes, when available):
+  - Broadcasts both needles via `VPBROADCASTB`.
+  - Processes 32-byte blocks: `VPCMPEQB` against both needles, `VPOR`, then
+    `VPMOVMSKB` to get a 32-bit mask.
+  - 5 instructions per loop iteration (vs 7 for SSE2) at 2x the throughput.
+  - `VZEROUPPER` before every return to avoid SSE/AVX transition penalties.
+- **SSE2 fallback** (inputs < 32 bytes, or CPUs without AVX2):
+  - Broadcasts via `PUNPCKLBW` + `PSHUFL`.
+  - Processes 16-byte blocks: `PCMPEQB`, `POR`, `PMOVMSKB`.
+  - Small inputs (<16 bytes) are handled with page-boundary-safe loads.
+- Both paths use `BSFL` (forward) / `BSRL` (reverse) for bit scanning.
+- Adapted from Go's `internal/bytealg/indexbyte_amd64.s`.
+
+**Fallback (other platforms):**
+- `indexByteTwo` uses two `bytes.IndexByte` calls with scope-limiting
+  (search `b1` first, then limit the `b2` search to `s[:i1]`).
+- `lastIndexByteTwo` uses a simple backward for loop.
+
+## Running tests
+
+```bash
+# Unit + exhaustive tests
+go test ./src/algo/ -run 'TestIndexByteTwo|TestLastIndexByteTwo' -v
+
+# Fuzz tests (run for 10 seconds each)
+go test ./src/algo/ -run '^$' -fuzz FuzzIndexByteTwo -fuzztime 10s
+go test ./src/algo/ -run '^$' -fuzz FuzzLastIndexByteTwo -fuzztime 10s
+
+# Cross-architecture: test amd64 on an arm64 Mac (via Rosetta)
+GOARCH=amd64 go test ./src/algo/ -run 'TestIndexByteTwo|TestLastIndexByteTwo' -v
+GOARCH=amd64 go test ./src/algo/ -run '^$' -fuzz FuzzIndexByteTwo -fuzztime 10s
+GOARCH=amd64 go test ./src/algo/ -run '^$' -fuzz FuzzLastIndexByteTwo -fuzztime 10s
+```
+
+## Running micro-benchmarks
+
+```bash
+# All indexByteTwo / lastIndexByteTwo benchmarks
+go test ./src/algo/ -bench 'IndexByteTwo' -benchmem
+
+# Specific size
+go test ./src/algo/ -bench 'IndexByteTwo_1000'
+```
+
+Each benchmark compares the SIMD `asm` implementation against reference
+implementations (`2xIndexByte` using `bytes.IndexByte`, and a simple `loop`).
+
+## Correctness verification
+
+The assembly is verified by three layers of testing:
+
+1. **Table-driven tests** — known inputs with expected outputs.
+2. **Exhaustive tests** — all lengths 0–256, every match position, no-match
+   cases, and both-bytes-present cases, compared against a simple loop
+   reference.
+3. **Fuzz tests** — randomized inputs via `testing.F`, compared against the
+   same loop reference.

src/algo/algo.go

@@ -321,22 +321,15 @@ type Algo func(caseSensitive bool, normalize bool, forward bool, input *util.Cha
 
 func trySkip(input *util.Chars, caseSensitive bool, b byte, from int) int {
 	byteArray := input.Bytes()[from:]
-	idx := bytes.IndexByte(byteArray, b)
+	// For case-insensitive search of a letter, search for both cases in one pass
-	if idx == 0 {
-		// Can't skip any further
-		return from
-	}
-	// We may need to search for the uppercase letter again. We don't have to
-	// consider normalization as we can be sure that this is an ASCII string.
 	if !caseSensitive && b >= 'a' && b <= 'z' {
-		if idx > 0 {
+		idx := indexByteTwo(byteArray, b, b-32)
-			byteArray = byteArray[:idx]
+		if idx < 0 {
-		}
+			return -1
-		uidx := bytes.IndexByte(byteArray, b-32)
-		if uidx >= 0 {
-			idx = uidx
 		}
+		return from + idx
 	}
+	idx := bytes.IndexByte(byteArray, b)
 	if idx < 0 {
 		return -1
 	}
@@ -380,14 +373,17 @@ func asciiFuzzyIndex(input *util.Chars, pattern []rune, caseSensitive bool) (int
 	}
 
 	// Find the last appearance of the last character of the pattern to limit the search scope
-	bu := b
-	if !caseSensitive && b >= 'a' && b <= 'z' {
-		bu = b - 32
-	}
 	scope := input.Bytes()[lastIdx:]
-	for offset := len(scope) - 1; offset > 0; offset-- {
+	if len(scope) > 1 {
-		if scope[offset] == b || scope[offset] == bu {
+		tail := scope[1:]
-			return firstIdx, lastIdx + offset + 1
+		var end int
+		if !caseSensitive && b >= 'a' && b <= 'z' {
+			end = lastIndexByteTwo(tail, b, b-32)
+		} else {
+			end = bytes.LastIndexByte(tail, b)
+		}
+		if end >= 0 {
+			return firstIdx, lastIdx + 1 + end + 1
 		}
 	}
 	return firstIdx, lastIdx + 1

src/algo/indexbyte2_amd64.go

@@ -0,0 +1,24 @@
+//go:build amd64
+
+package algo
+
+var _useAVX2 bool
+
+func init() {
+	_useAVX2 = cpuHasAVX2()
+}
+
+//go:noescape
+func cpuHasAVX2() bool
+
+// indexByteTwo returns the index of the first occurrence of b1 or b2 in s,
+// or -1 if neither is present. Uses AVX2 when available, SSE2 otherwise.
+//
+//go:noescape
+func indexByteTwo(s []byte, b1, b2 byte) int
+
+// lastIndexByteTwo returns the index of the last occurrence of b1 or b2 in s,
+// or -1 if neither is present. Uses AVX2 when available, SSE2 otherwise.
+//
+//go:noescape
+func lastIndexByteTwo(s []byte, b1, b2 byte) int

src/algo/indexbyte2_amd64.s

@@ -0,0 +1,377 @@
+#include "textflag.h"
+
+// func cpuHasAVX2() bool
+//
+// Checks CPUID and XGETBV for AVX2 + OS YMM support.
+TEXT ·cpuHasAVX2(SB),NOSPLIT,$0-1
+	MOVQ	BX, R8          // save BX (callee-saved, clobbered by CPUID)
+
+	// Check max CPUID leaf >= 7
+	MOVL	$0, AX
+	CPUID
+	CMPL	AX, $7
+	JL	cpuid_no
+
+	// Check OSXSAVE (CPUID.1:ECX bit 27)
+	MOVL	$1, AX
+	CPUID
+	TESTL	$(1<<27), CX
+	JZ	cpuid_no
+
+	// Check AVX2 (CPUID.7.0:EBX bit 5)
+	MOVL	$7, AX
+	MOVL	$0, CX
+	CPUID
+	TESTL	$(1<<5), BX
+	JZ	cpuid_no
+
+	// Check OS YMM state support via XGETBV
+	MOVL	$0, CX
+	BYTE	$0x0F; BYTE $0x01; BYTE $0xD0  // XGETBV → EDX:EAX
+	ANDL	$6, AX          // bits 1 (XMM) and 2 (YMM)
+	CMPL	AX, $6
+	JNE	cpuid_no
+
+	MOVQ	R8, BX          // restore BX
+	MOVB	$1, ret+0(FP)
+	RET
+
+cpuid_no:
+	MOVQ	R8, BX
+	MOVB	$0, ret+0(FP)
+	RET
+
+// func indexByteTwo(s []byte, b1, b2 byte) int
+//
+// Returns the index of the first occurrence of b1 or b2 in s, or -1.
+// Uses AVX2 (32 bytes/iter) when available, SSE2 (16 bytes/iter) otherwise.
+TEXT ·indexByteTwo(SB),NOSPLIT,$0-40
+	MOVQ	s_base+0(FP), SI
+	MOVQ	s_len+8(FP), BX
+	MOVBLZX	b1+24(FP), AX
+	MOVBLZX	b2+25(FP), CX
+	LEAQ	ret+32(FP), R8
+
+	TESTQ	BX, BX
+	JEQ	fwd_failure
+
+	// Try AVX2 for inputs >= 32 bytes
+	CMPQ	BX, $32
+	JLT	fwd_sse2
+	CMPB	·_useAVX2(SB), $1
+	JNE	fwd_sse2
+
+	// ====== AVX2 forward search ======
+	MOVD	AX, X0
+	VPBROADCASTB	X0, Y0       // Y0 = splat(b1)
+	MOVD	CX, X1
+	VPBROADCASTB	X1, Y1       // Y1 = splat(b2)
+
+	MOVQ	SI, DI
+	LEAQ	-32(SI)(BX*1), AX    // AX = last valid 32-byte chunk
+	JMP	fwd_avx2_entry
+
+fwd_avx2_loop:
+	VMOVDQU	(DI), Y2
+	VPCMPEQB	Y0, Y2, Y3
+	VPCMPEQB	Y1, Y2, Y4
+	VPOR	Y3, Y4, Y3
+	VPMOVMSKB	Y3, DX
+	BSFL	DX, DX
+	JNZ	fwd_avx2_success
+	ADDQ	$32, DI
+
+fwd_avx2_entry:
+	CMPQ	DI, AX
+	JB	fwd_avx2_loop
+
+	// Last 32-byte chunk (may overlap with previous)
+	MOVQ	AX, DI
+	VMOVDQU	(AX), Y2
+	VPCMPEQB	Y0, Y2, Y3
+	VPCMPEQB	Y1, Y2, Y4
+	VPOR	Y3, Y4, Y3
+	VPMOVMSKB	Y3, DX
+	BSFL	DX, DX
+	JNZ	fwd_avx2_success
+
+	MOVQ	$-1, (R8)
+	VZEROUPPER
+	RET
+
+fwd_avx2_success:
+	SUBQ	SI, DI
+	ADDQ	DX, DI
+	MOVQ	DI, (R8)
+	VZEROUPPER
+	RET
+
+	// ====== SSE2 forward search (< 32 bytes or no AVX2) ======
+
+fwd_sse2:
+	// Broadcast b1 into X0
+	MOVD	AX, X0
+	PUNPCKLBW	X0, X0
+	PUNPCKLBW	X0, X0
+	PSHUFL	$0, X0, X0
+
+	// Broadcast b2 into X4
+	MOVD	CX, X4
+	PUNPCKLBW	X4, X4
+	PUNPCKLBW	X4, X4
+	PSHUFL	$0, X4, X4
+
+	CMPQ	BX, $16
+	JLT	fwd_small
+
+	MOVQ	SI, DI
+	LEAQ	-16(SI)(BX*1), AX
+	JMP	fwd_sseloopentry
+
+fwd_sseloop:
+	MOVOU	(DI), X1
+	MOVOU	X1, X2
+	PCMPEQB	X0, X1
+	PCMPEQB	X4, X2
+	POR	X2, X1
+	PMOVMSKB	X1, DX
+	BSFL	DX, DX
+	JNZ	fwd_ssesuccess
+	ADDQ	$16, DI
+
+fwd_sseloopentry:
+	CMPQ	DI, AX
+	JB	fwd_sseloop
+
+	// Search the last 16-byte chunk (may overlap)
+	MOVQ	AX, DI
+	MOVOU	(AX), X1
+	MOVOU	X1, X2
+	PCMPEQB	X0, X1
+	PCMPEQB	X4, X2
+	POR	X2, X1
+	PMOVMSKB	X1, DX
+	BSFL	DX, DX
+	JNZ	fwd_ssesuccess
+
+fwd_failure:
+	MOVQ	$-1, (R8)
+	RET
+
+fwd_ssesuccess:
+	SUBQ	SI, DI
+	ADDQ	DX, DI
+	MOVQ	DI, (R8)
+	RET
+
+fwd_small:
+	// Check if loading 16 bytes from SI would cross a page boundary
+	LEAQ	16(SI), AX
+	TESTW	$0xff0, AX
+	JEQ	fwd_endofpage
+
+	MOVOU	(SI), X1
+	MOVOU	X1, X2
+	PCMPEQB	X0, X1
+	PCMPEQB	X4, X2
+	POR	X2, X1
+	PMOVMSKB	X1, DX
+	BSFL	DX, DX
+	JZ	fwd_failure
+	CMPL	DX, BX
+	JAE	fwd_failure
+	MOVQ	DX, (R8)
+	RET
+
+fwd_endofpage:
+	MOVOU	-16(SI)(BX*1), X1
+	MOVOU	X1, X2
+	PCMPEQB	X0, X1
+	PCMPEQB	X4, X2
+	POR	X2, X1
+	PMOVMSKB	X1, DX
+	MOVL	BX, CX
+	SHLL	CX, DX
+	SHRL	$16, DX
+	BSFL	DX, DX
+	JZ	fwd_failure
+	MOVQ	DX, (R8)
+	RET
+
+// func lastIndexByteTwo(s []byte, b1, b2 byte) int
+//
+// Returns the index of the last occurrence of b1 or b2 in s, or -1.
+// Uses AVX2 (32 bytes/iter) when available, SSE2 (16 bytes/iter) otherwise.
+TEXT ·lastIndexByteTwo(SB),NOSPLIT,$0-40
+	MOVQ	s_base+0(FP), SI
+	MOVQ	s_len+8(FP), BX
+	MOVBLZX	b1+24(FP), AX
+	MOVBLZX	b2+25(FP), CX
+	LEAQ	ret+32(FP), R8
+
+	TESTQ	BX, BX
+	JEQ	back_failure
+
+	// Try AVX2 for inputs >= 32 bytes
+	CMPQ	BX, $32
+	JLT	back_sse2
+	CMPB	·_useAVX2(SB), $1
+	JNE	back_sse2
+
+	// ====== AVX2 backward search ======
+	MOVD	AX, X0
+	VPBROADCASTB	X0, Y0
+	MOVD	CX, X1
+	VPBROADCASTB	X1, Y1
+
+	// DI = start of last 32-byte chunk
+	LEAQ	-32(SI)(BX*1), DI
+
+back_avx2_loop:
+	CMPQ	DI, SI
+	JBE	back_avx2_first
+
+	VMOVDQU	(DI), Y2
+	VPCMPEQB	Y0, Y2, Y3
+	VPCMPEQB	Y1, Y2, Y4
+	VPOR	Y3, Y4, Y3
+	VPMOVMSKB	Y3, DX
+	BSRL	DX, DX
+	JNZ	back_avx2_success
+	SUBQ	$32, DI
+	JMP	back_avx2_loop
+
+back_avx2_first:
+	// First 32 bytes (DI <= SI, load from SI)
+	VMOVDQU	(SI), Y2
+	VPCMPEQB	Y0, Y2, Y3
+	VPCMPEQB	Y1, Y2, Y4
+	VPOR	Y3, Y4, Y3
+	VPMOVMSKB	Y3, DX
+	BSRL	DX, DX
+	JNZ	back_avx2_firstsuccess
+
+	MOVQ	$-1, (R8)
+	VZEROUPPER
+	RET
+
+back_avx2_success:
+	SUBQ	SI, DI
+	ADDQ	DX, DI
+	MOVQ	DI, (R8)
+	VZEROUPPER
+	RET
+
+back_avx2_firstsuccess:
+	MOVQ	DX, (R8)
+	VZEROUPPER
+	RET
+
+	// ====== SSE2 backward search (< 32 bytes or no AVX2) ======
+
+back_sse2:
+	// Broadcast b1 into X0
+	MOVD	AX, X0
+	PUNPCKLBW	X0, X0
+	PUNPCKLBW	X0, X0
+	PSHUFL	$0, X0, X0
+
+	// Broadcast b2 into X4
+	MOVD	CX, X4
+	PUNPCKLBW	X4, X4
+	PUNPCKLBW	X4, X4
+	PSHUFL	$0, X4, X4
+
+	CMPQ	BX, $16
+	JLT	back_small
+
+	// DI = start of last 16-byte chunk
+	LEAQ	-16(SI)(BX*1), DI
+
+back_sseloop:
+	CMPQ	DI, SI
+	JBE	back_ssefirst
+
+	MOVOU	(DI), X1
+	MOVOU	X1, X2
+	PCMPEQB	X0, X1
+	PCMPEQB	X4, X2
+	POR	X2, X1
+	PMOVMSKB	X1, DX
+	BSRL	DX, DX
+	JNZ	back_ssesuccess
+	SUBQ	$16, DI
+	JMP	back_sseloop
+
+back_ssefirst:
+	// First 16 bytes (DI <= SI, load from SI)
+	MOVOU	(SI), X1
+	MOVOU	X1, X2
+	PCMPEQB	X0, X1
+	PCMPEQB	X4, X2
+	POR	X2, X1
+	PMOVMSKB	X1, DX
+	BSRL	DX, DX
+	JNZ	back_ssefirstsuccess
+
+back_failure:
+	MOVQ	$-1, (R8)
+	RET
+
+back_ssesuccess:
+	SUBQ	SI, DI
+	ADDQ	DX, DI
+	MOVQ	DI, (R8)
+	RET
+
+back_ssefirstsuccess:
+	// DX = byte offset from base
+	MOVQ	DX, (R8)
+	RET
+
+back_small:
+	// Check page boundary
+	LEAQ	16(SI), AX
+	TESTW	$0xff0, AX
+	JEQ	back_endofpage
+
+	MOVOU	(SI), X1
+	MOVOU	X1, X2
+	PCMPEQB	X0, X1
+	PCMPEQB	X4, X2
+	POR	X2, X1
+	PMOVMSKB	X1, DX
+	// Mask to first BX bytes: keep bits 0..BX-1
+	MOVL	$1, AX
+	MOVL	BX, CX
+	SHLL	CX, AX
+	DECL	AX
+	ANDL	AX, DX
+	BSRL	DX, DX
+	JZ	back_failure
+	MOVQ	DX, (R8)
+	RET
+
+back_endofpage:
+	// Load 16 bytes ending at base+n
+	MOVOU	-16(SI)(BX*1), X1
+	MOVOU	X1, X2
+	PCMPEQB	X0, X1
+	PCMPEQB	X4, X2
+	POR	X2, X1
+	PMOVMSKB	X1, DX
+	// Bits correspond to bytes [base+n-16, base+n).
+	// We want original bytes [0, n), which are bits [16-n, 16).
+	// Mask: keep bits (16-n) through 15.
+	MOVL	$16, CX
+	SUBL	BX, CX
+	SHRL	CX, DX
+	SHLL	CX, DX
+	BSRL	DX, DX
+	JZ	back_failure
+	// DX is the bit position in the loaded chunk.
+	// Original byte index = DX - (16 - n) = DX + n - 16
+	ADDL	BX, DX
+	SUBL	$16, DX
+	MOVQ	DX, (R8)
+	RET

src/algo/indexbyte2_arm64.go

@@ -0,0 +1,17 @@
+//go:build arm64
+
+package algo
+
+// indexByteTwo returns the index of the first occurrence of b1 or b2 in s,
+// or -1 if neither is present. Implemented in assembly using ARM64 NEON
+// to search for both bytes in a single pass.
+//
+//go:noescape
+func indexByteTwo(s []byte, b1, b2 byte) int
+
+// lastIndexByteTwo returns the index of the last occurrence of b1 or b2 in s,
+// or -1 if neither is present. Implemented in assembly using ARM64 NEON,
+// scanning backward.
+//
+//go:noescape
+func lastIndexByteTwo(s []byte, b1, b2 byte) int

src/algo/indexbyte2_arm64.s

@@ -0,0 +1,249 @@
+#include "textflag.h"
+
+// func indexByteTwo(s []byte, b1, b2 byte) int
+//
+// Returns the index of the first occurrence of b1 or b2 in s, or -1.
+// Uses ARM64 NEON to search for both bytes in a single pass over the data.
+// Adapted from Go's internal/bytealg/indexbyte_arm64.s (single-byte version).
+TEXT ·indexByteTwo(SB),NOSPLIT,$0-40
+	MOVD	s_base+0(FP), R0
+	MOVD	s_len+8(FP), R2
+	MOVBU	b1+24(FP), R1
+	MOVBU	b2+25(FP), R7
+	MOVD	$ret+32(FP), R8
+
+	// Core algorithm:
+	// For each 32-byte chunk we calculate a 64-bit syndrome value,
+	// with two bits per byte. We compare against both b1 and b2,
+	// OR the results, then use the same syndrome extraction as
+	// Go's IndexByte.
+
+	CBZ	R2, fail
+	MOVD	R0, R11
+	// Magic constant 0x40100401 allows us to identify which lane matches.
+	// Each byte in the group of 4 gets a distinct bit: 1, 4, 16, 64.
+	MOVD	$0x40100401, R5
+	VMOV	R1, V0.B16    // V0 = splat(b1)
+	VMOV	R7, V7.B16    // V7 = splat(b2)
+	// Work with aligned 32-byte chunks
+	BIC	$0x1f, R0, R3
+	VMOV	R5, V5.S4
+	ANDS	$0x1f, R0, R9
+	AND	$0x1f, R2, R10
+	BEQ	loop
+
+	// Input string is not 32-byte aligned. Process the first
+	// aligned 32-byte block and mask off bytes before our start.
+	VLD1.P	(R3), [V1.B16, V2.B16]
+	SUB	$0x20, R9, R4
+	ADDS	R4, R2, R2
+	// Compare against both needles
+	VCMEQ	V0.B16, V1.B16, V3.B16  // b1 vs first 16 bytes
+	VCMEQ	V7.B16, V1.B16, V8.B16  // b2 vs first 16 bytes
+	VORR	V8.B16, V3.B16, V3.B16  // combine
+	VCMEQ	V0.B16, V2.B16, V4.B16  // b1 vs second 16 bytes
+	VCMEQ	V7.B16, V2.B16, V9.B16  // b2 vs second 16 bytes
+	VORR	V9.B16, V4.B16, V4.B16  // combine
+	// Build syndrome
+	VAND	V5.B16, V3.B16, V3.B16
+	VAND	V5.B16, V4.B16, V4.B16
+	VADDP	V4.B16, V3.B16, V6.B16
+	VADDP	V6.B16, V6.B16, V6.B16
+	VMOV	V6.D[0], R6
+	// Clear the irrelevant lower bits
+	LSL	$1, R9, R4
+	LSR	R4, R6, R6
+	LSL	R4, R6, R6
+	// The first block can also be the last
+	BLS	masklast
+	// Have we found something already?
+	CBNZ	R6, tail
+
+loop:
+	VLD1.P	(R3), [V1.B16, V2.B16]
+	SUBS	$0x20, R2, R2
+	// Compare against both needles, OR results
+	VCMEQ	V0.B16, V1.B16, V3.B16
+	VCMEQ	V7.B16, V1.B16, V8.B16
+	VORR	V8.B16, V3.B16, V3.B16
+	VCMEQ	V0.B16, V2.B16, V4.B16
+	VCMEQ	V7.B16, V2.B16, V9.B16
+	VORR	V9.B16, V4.B16, V4.B16
+	// If we're out of data we finish regardless of the result
+	BLS	end
+	// Fast check: OR both halves and check for any match
+	VORR	V4.B16, V3.B16, V6.B16
+	VADDP	V6.D2, V6.D2, V6.D2
+	VMOV	V6.D[0], R6
+	CBZ	R6, loop
+
+end:
+	// Found something or out of data — build full syndrome
+	VAND	V5.B16, V3.B16, V3.B16
+	VAND	V5.B16, V4.B16, V4.B16
+	VADDP	V4.B16, V3.B16, V6.B16
+	VADDP	V6.B16, V6.B16, V6.B16
+	VMOV	V6.D[0], R6
+	// Only mask for the last block
+	BHS	tail
+
+masklast:
+	// Clear irrelevant upper bits
+	ADD	R9, R10, R4
+	AND	$0x1f, R4, R4
+	SUB	$0x20, R4, R4
+	NEG	R4<<1, R4
+	LSL	R4, R6, R6
+	LSR	R4, R6, R6
+
+tail:
+	CBZ	R6, fail
+	RBIT	R6, R6
+	SUB	$0x20, R3, R3
+	CLZ	R6, R6
+	ADD	R6>>1, R3, R0
+	SUB	R11, R0, R0
+	MOVD	R0, (R8)
+	RET
+
+fail:
+	MOVD	$-1, R0
+	MOVD	R0, (R8)
+	RET
+
+// func lastIndexByteTwo(s []byte, b1, b2 byte) int
+//
+// Returns the index of the last occurrence of b1 or b2 in s, or -1.
+// Scans backward using ARM64 NEON.
+TEXT ·lastIndexByteTwo(SB),NOSPLIT,$0-40
+	MOVD	s_base+0(FP), R0
+	MOVD	s_len+8(FP), R2
+	MOVBU	b1+24(FP), R1
+	MOVBU	b2+25(FP), R7
+	MOVD	$ret+32(FP), R8
+
+	CBZ	R2, lfail
+	MOVD	R0, R11          // save base
+	ADD	R0, R2, R12      // R12 = end = base + len
+	MOVD	$0x40100401, R5
+	VMOV	R1, V0.B16       // V0 = splat(b1)
+	VMOV	R7, V7.B16       // V7 = splat(b2)
+	VMOV	R5, V5.S4
+
+	// Align: find the aligned block containing the last byte
+	SUB	$1, R12, R3
+	BIC	$0x1f, R3, R3    // R3 = start of aligned block containing last byte
+
+	// --- Process tail block ---
+	VLD1	(R3), [V1.B16, V2.B16]
+	VCMEQ	V0.B16, V1.B16, V3.B16
+	VCMEQ	V7.B16, V1.B16, V8.B16
+	VORR	V8.B16, V3.B16, V3.B16
+	VCMEQ	V0.B16, V2.B16, V4.B16
+	VCMEQ	V7.B16, V2.B16, V9.B16
+	VORR	V9.B16, V4.B16, V4.B16
+	VAND	V5.B16, V3.B16, V3.B16
+	VAND	V5.B16, V4.B16, V4.B16
+	VADDP	V4.B16, V3.B16, V6.B16
+	VADDP	V6.B16, V6.B16, V6.B16
+	VMOV	V6.D[0], R6
+
+	// Mask upper bits (bytes past end of slice)
+	// tail_bytes = end - R3 (1..32)
+	SUB	R3, R12, R10     // R10 = tail_bytes
+	MOVD	$64, R4
+	SUB	R10<<1, R4, R4   // R4 = 64 - 2*tail_bytes
+	LSL	R4, R6, R6
+	LSR	R4, R6, R6
+
+	// Is this also the head block?
+	CMP	R11, R3          // R3 - R11
+	BLO	lmaskfirst       // R3 < base: head+tail in same block
+	BEQ	ltailonly         // R3 == base: single aligned block
+
+	// R3 > base: more blocks before this one
+	CBNZ	R6, llast
+	B	lbacksetup
+
+ltailonly:
+	// Single block, already masked upper bits
+	CBNZ	R6, llast
+	B	lfail
+
+lmaskfirst:
+	// Mask lower bits (bytes before start of slice)
+	SUB	R3, R11, R4      // R4 = base - R3
+	LSL	$1, R4, R4
+	LSR	R4, R6, R6
+	LSL	R4, R6, R6
+	CBNZ	R6, llast
+	B	lfail
+
+lbacksetup:
+	SUB	$0x20, R3
+
+lbackloop:
+	VLD1	(R3), [V1.B16, V2.B16]
+	VCMEQ	V0.B16, V1.B16, V3.B16
+	VCMEQ	V7.B16, V1.B16, V8.B16
+	VORR	V8.B16, V3.B16, V3.B16
+	VCMEQ	V0.B16, V2.B16, V4.B16
+	VCMEQ	V7.B16, V2.B16, V9.B16
+	VORR	V9.B16, V4.B16, V4.B16
+	// Quick check: any match in this block?
+	VORR	V4.B16, V3.B16, V6.B16
+	VADDP	V6.D2, V6.D2, V6.D2
+	VMOV	V6.D[0], R6
+
+	// Is this a head block? (R3 < base)
+	CMP	R11, R3
+	BLO	lheadblock
+
+	// Full block (R3 >= base)
+	CBNZ	R6, lbackfound
+	// More blocks?
+	BEQ	lfail            // R3 == base, no more
+	SUB	$0x20, R3
+	B	lbackloop
+
+lbackfound:
+	// Build full syndrome
+	VAND	V5.B16, V3.B16, V3.B16
+	VAND	V5.B16, V4.B16, V4.B16
+	VADDP	V4.B16, V3.B16, V6.B16
+	VADDP	V6.B16, V6.B16, V6.B16
+	VMOV	V6.D[0], R6
+	B	llast
+
+lheadblock:
+	// R3 < base. Build full syndrome if quick check had a match.
+	CBZ	R6, lfail
+	VAND	V5.B16, V3.B16, V3.B16
+	VAND	V5.B16, V4.B16, V4.B16
+	VADDP	V4.B16, V3.B16, V6.B16
+	VADDP	V6.B16, V6.B16, V6.B16
+	VMOV	V6.D[0], R6
+	// Mask lower bits
+	SUB	R3, R11, R4      // R4 = base - R3
+	LSL	$1, R4, R4
+	LSR	R4, R6, R6
+	LSL	R4, R6, R6
+	CBZ	R6, lfail
+
+llast:
+	// Find last match: highest set bit in syndrome
+	// Syndrome has bit 2i set for matching byte i.
+	// CLZ gives leading zeros; byte_offset = (63 - CLZ) / 2.
+	CLZ	R6, R6
+	MOVD	$63, R4
+	SUB	R6, R4, R6       // R6 = 63 - CLZ = bit position
+	LSR	$1, R6            // R6 = byte offset within block
+	ADD	R3, R6, R0        // R0 = absolute address
+	SUB	R11, R0, R0       // R0 = slice index
+	MOVD	R0, (R8)
+	RET
+
+lfail:
+	MOVD	$-1, R0
+	MOVD	R0, (R8)
+	RET

src/algo/indexbyte2_other.go

@@ -0,0 +1,33 @@
+//go:build !arm64 && !amd64
+
+package algo
+
+import "bytes"
+
+// indexByteTwo returns the index of the first occurrence of b1 or b2 in s,
+// or -1 if neither is present.
+func indexByteTwo(s []byte, b1, b2 byte) int {
+	i1 := bytes.IndexByte(s, b1)
+	if i1 == 0 {
+		return 0
+	}
+	scope := s
+	if i1 > 0 {
+		scope = s[:i1]
+	}
+	if i2 := bytes.IndexByte(scope, b2); i2 >= 0 {
+		return i2
+	}
+	return i1
+}
+
+// lastIndexByteTwo returns the index of the last occurrence of b1 or b2 in s,
+// or -1 if neither is present.
+func lastIndexByteTwo(s []byte, b1, b2 byte) int {
+	for i := len(s) - 1; i >= 0; i-- {
+		if s[i] == b1 || s[i] == b2 {
+			return i
+		}
+	}
+	return -1
+}

src/algo/indexbyte2_test.go

@@ -0,0 +1,259 @@
+package algo
+
+import (
+	"bytes"
+	"testing"
+)
+
+func TestIndexByteTwo(t *testing.T) {
+	tests := []struct {
+		name string
+		s    string
+		b1   byte
+		b2   byte
+		want int
+	}{
+		{"empty", "", 'a', 'b', -1},
+		{"single_b1", "a", 'a', 'b', 0},
+		{"single_b2", "b", 'a', 'b', 0},
+		{"single_none", "c", 'a', 'b', -1},
+		{"b1_first", "xaxb", 'a', 'b', 1},
+		{"b2_first", "xbxa", 'a', 'b', 1},
+		{"same_byte", "xxa", 'a', 'a', 2},
+		{"at_end", "xxxxa", 'a', 'b', 4},
+		{"not_found", "xxxxxxxx", 'a', 'b', -1},
+		{"long_b1_at_3000", string(make([]byte, 3000)) + "a" + string(make([]byte, 1000)), 'a', 'b', 3000},
+		{"long_b2_at_3000", string(make([]byte, 3000)) + "b" + string(make([]byte, 1000)), 'a', 'b', 3000},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := indexByteTwo([]byte(tt.s), tt.b1, tt.b2)
+			if got != tt.want {
+				t.Errorf("indexByteTwo(%q, %c, %c) = %d, want %d", tt.s[:min(len(tt.s), 40)], tt.b1, tt.b2, got, tt.want)
+			}
+		})
+	}
+
+	// Exhaustive test: compare against loop reference for various lengths,
+	// including sizes around SIMD block boundaries (16, 32, 64).
+	for n := 0; n <= 256; n++ {
+		data := make([]byte, n)
+		for i := range data {
+			data[i] = byte('c' + (i % 20))
+		}
+		// Test with match at every position
+		for pos := 0; pos < n; pos++ {
+			for _, b := range []byte{'A', 'B'} {
+				data[pos] = b
+				got := indexByteTwo(data, 'A', 'B')
+				want := loopIndexByteTwo(data, 'A', 'B')
+				if got != want {
+					t.Fatalf("indexByteTwo(len=%d, match=%c@%d) = %d, want %d", n, b, pos, got, want)
+				}
+				data[pos] = byte('c' + (pos % 20))
+			}
+		}
+		// Test with no match
+		got := indexByteTwo(data, 'A', 'B')
+		if got != -1 {
+			t.Fatalf("indexByteTwo(len=%d, no match) = %d, want -1", n, got)
+		}
+		// Test with both bytes present
+		if n >= 2 {
+			data[n/3] = 'A'
+			data[n*2/3] = 'B'
+			got := indexByteTwo(data, 'A', 'B')
+			want := loopIndexByteTwo(data, 'A', 'B')
+			if got != want {
+				t.Fatalf("indexByteTwo(len=%d, both@%d,%d) = %d, want %d", n, n/3, n*2/3, got, want)
+			}
+			data[n/3] = byte('c' + ((n / 3) % 20))
+			data[n*2/3] = byte('c' + ((n * 2 / 3) % 20))
+		}
+	}
+}
+
+func TestLastIndexByteTwo(t *testing.T) {
+	tests := []struct {
+		name string
+		s    string
+		b1   byte
+		b2   byte
+		want int
+	}{
+		{"empty", "", 'a', 'b', -1},
+		{"single_b1", "a", 'a', 'b', 0},
+		{"single_b2", "b", 'a', 'b', 0},
+		{"single_none", "c", 'a', 'b', -1},
+		{"b1_last", "xbxa", 'a', 'b', 3},
+		{"b2_last", "xaxb", 'a', 'b', 3},
+		{"same_byte", "axx", 'a', 'a', 0},
+		{"at_start", "axxxx", 'a', 'b', 0},
+		{"both_present", "axbx", 'a', 'b', 2},
+		{"not_found", "xxxxxxxx", 'a', 'b', -1},
+		{"long_b1_at_3000", string(make([]byte, 3000)) + "a" + string(make([]byte, 1000)), 'a', 'b', 3000},
+		{"long_b2_at_end", string(make([]byte, 4000)) + "b", 'a', 'b', 4000},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := lastIndexByteTwo([]byte(tt.s), tt.b1, tt.b2)
+			if got != tt.want {
+				t.Errorf("lastIndexByteTwo(%q, %c, %c) = %d, want %d", tt.s[:min(len(tt.s), 40)], tt.b1, tt.b2, got, tt.want)
+			}
+		})
+	}
+
+	// Exhaustive test against loop reference
+	for n := 0; n <= 256; n++ {
+		data := make([]byte, n)
+		for i := range data {
+			data[i] = byte('c' + (i % 20))
+		}
+		for pos := 0; pos < n; pos++ {
+			for _, b := range []byte{'A', 'B'} {
+				data[pos] = b
+				got := lastIndexByteTwo(data, 'A', 'B')
+				want := refLastIndexByteTwo(data, 'A', 'B')
+				if got != want {
+					t.Fatalf("lastIndexByteTwo(len=%d, match=%c@%d) = %d, want %d", n, b, pos, got, want)
+				}
+				data[pos] = byte('c' + (pos % 20))
+			}
+		}
+		// No match
+		got := lastIndexByteTwo(data, 'A', 'B')
+		if got != -1 {
+			t.Fatalf("lastIndexByteTwo(len=%d, no match) = %d, want -1", n, got)
+		}
+		// Both bytes present
+		if n >= 2 {
+			data[n/3] = 'A'
+			data[n*2/3] = 'B'
+			got := lastIndexByteTwo(data, 'A', 'B')
+			want := refLastIndexByteTwo(data, 'A', 'B')
+			if got != want {
+				t.Fatalf("lastIndexByteTwo(len=%d, both@%d,%d) = %d, want %d", n, n/3, n*2/3, got, want)
+			}
+			data[n/3] = byte('c' + ((n / 3) % 20))
+			data[n*2/3] = byte('c' + ((n * 2 / 3) % 20))
+		}
+	}
+}
+
+func FuzzIndexByteTwo(f *testing.F) {
+	f.Add([]byte("hello world"), byte('o'), byte('l'))
+	f.Add([]byte(""), byte('a'), byte('b'))
+	f.Add([]byte("aaa"), byte('a'), byte('a'))
+	f.Fuzz(func(t *testing.T, data []byte, b1, b2 byte) {
+		got := indexByteTwo(data, b1, b2)
+		want := loopIndexByteTwo(data, b1, b2)
+		if got != want {
+			t.Errorf("indexByteTwo(len=%d, b1=%d, b2=%d) = %d, want %d", len(data), b1, b2, got, want)
+		}
+	})
+}
+
+func FuzzLastIndexByteTwo(f *testing.F) {
+	f.Add([]byte("hello world"), byte('o'), byte('l'))
+	f.Add([]byte(""), byte('a'), byte('b'))
+	f.Add([]byte("aaa"), byte('a'), byte('a'))
+	f.Fuzz(func(t *testing.T, data []byte, b1, b2 byte) {
+		got := lastIndexByteTwo(data, b1, b2)
+		want := refLastIndexByteTwo(data, b1, b2)
+		if got != want {
+			t.Errorf("lastIndexByteTwo(len=%d, b1=%d, b2=%d) = %d, want %d", len(data), b1, b2, got, want)
+		}
+	})
+}
+
+// Reference implementations for correctness checking
+func refIndexByteTwo(s []byte, b1, b2 byte) int {
+	i1 := bytes.IndexByte(s, b1)
+	if i1 == 0 {
+		return 0
+	}
+	scope := s
+	if i1 > 0 {
+		scope = s[:i1]
+	}
+	if i2 := bytes.IndexByte(scope, b2); i2 >= 0 {
+		return i2
+	}
+	return i1
+}
+
+func loopIndexByteTwo(s []byte, b1, b2 byte) int {
+	for i, b := range s {
+		if b == b1 || b == b2 {
+			return i
+		}
+	}
+	return -1
+}
+
+func refLastIndexByteTwo(s []byte, b1, b2 byte) int {
+	for i := len(s) - 1; i >= 0; i-- {
+		if s[i] == b1 || s[i] == b2 {
+			return i
+		}
+	}
+	return -1
+}
+
+func benchIndexByteTwo(b *testing.B, size int, pos int) {
+	data := make([]byte, size)
+	for i := range data {
+		data[i] = byte('a' + (i % 20))
+	}
+	data[pos] = 'Z'
+
+	type impl struct {
+		name string
+		fn   func([]byte, byte, byte) int
+	}
+	impls := []impl{
+		{"asm", indexByteTwo},
+		{"2xIndexByte", refIndexByteTwo},
+		{"loop", loopIndexByteTwo},
+	}
+	for _, im := range impls {
+		b.Run(im.name, func(b *testing.B) {
+			for i := 0; i < b.N; i++ {
+				im.fn(data, 'Z', 'z')
+			}
+		})
+	}
+}
+
+func benchLastIndexByteTwo(b *testing.B, size int, pos int) {
+	data := make([]byte, size)
+	for i := range data {
+		data[i] = byte('a' + (i % 20))
+	}
+	data[pos] = 'Z'
+
+	type impl struct {
+		name string
+		fn   func([]byte, byte, byte) int
+	}
+	impls := []impl{
+		{"asm", lastIndexByteTwo},
+		{"loop", refLastIndexByteTwo},
+	}
+	for _, im := range impls {
+		b.Run(im.name, func(b *testing.B) {
+			for i := 0; i < b.N; i++ {
+				im.fn(data, 'Z', 'z')
+			}
+		})
+	}
+}
+
+func BenchmarkIndexByteTwo_10(b *testing.B)       { benchIndexByteTwo(b, 10, 8) }
+func BenchmarkIndexByteTwo_100(b *testing.B)      { benchIndexByteTwo(b, 100, 80) }
+func BenchmarkIndexByteTwo_1000(b *testing.B)     { benchIndexByteTwo(b, 1000, 800) }
+func BenchmarkLastIndexByteTwo_10(b *testing.B)   { benchLastIndexByteTwo(b, 10, 2) }
+func BenchmarkLastIndexByteTwo_100(b *testing.B)  { benchLastIndexByteTwo(b, 100, 20) }
+func BenchmarkLastIndexByteTwo_1000(b *testing.B) { benchLastIndexByteTwo(b, 1000, 200) }

src/chunklist.go

@@ -52,6 +52,20 @@ func (cl *ChunkList) lastChunk() *Chunk {
 	return cl.chunks[len(cl.chunks)-1]
 }
 
+// GetItems returns the first n items from the given chunks
+func GetItems(chunks []*Chunk, n int) []Item {
+	items := make([]Item, 0, n)
+	for _, chunk := range chunks {
+		for i := 0; i < chunk.count && len(items) < n; i++ {
+			items = append(items, chunk.items[i])
+		}
+		if len(items) >= n {
+			break
+		}
+	}
+	return items
+}
+
 // CountItems returns the total number of Items
 func CountItems(cs []*Chunk) int {
 	if len(cs) == 0 {
@@ -85,6 +99,21 @@ func (cl *ChunkList) Clear() {
 	cl.mutex.Unlock()
 }
 
+// ForEachItem iterates all items and applies fn to each one.
+// The done callback runs under the lock to safely update shared state.
+func (cl *ChunkList) ForEachItem(fn func(*Item), done func()) {
+	cl.mutex.Lock()
+	for _, chunk := range cl.chunks {
+		for i := 0; i < chunk.count; i++ {
+			fn(&chunk.items[i])
+		}
+	}
+	if done != nil {
+		done()
+	}
+	cl.mutex.Unlock()
+}
+
 // Snapshot returns immutable snapshot of the ChunkList
 func (cl *ChunkList) Snapshot(tail int) ([]*Chunk, int, bool) {
 	cl.mutex.Lock()

src/constants.go

@@ -39,7 +39,7 @@ const (
 	progressMinDuration     = 200 * time.Millisecond
 
 	// Capacity of each chunk
-	chunkSize int = 100
+	chunkSize int = 1000
 
 	// Pre-allocated memory slices to minimize GC
 	slab16Size int = 100 * 1024 // 200KB * 32 = 12.8MB
@@ -65,7 +65,6 @@ const (
 	EvtSearchNew
 	EvtSearchProgress
 	EvtSearchFin
-	EvtHeader
 	EvtReady
 	EvtQuit
 )

src/core.go

@@ -2,6 +2,7 @@
 package fzf
 
 import (
+	"fmt"
 	"maps"
 	"os"
 	"sync"
@@ -17,7 +18,6 @@ Reader   -> EvtReadNew        -> Matcher  (restart)
 Terminal -> EvtSearchNew:bool -> Matcher  (restart)
 Matcher  -> EvtSearchProgress -> Terminal (update info)
 Matcher  -> EvtSearchFin      -> Terminal (update list)
-Matcher  -> EvtHeader         -> Terminal (update header)
 */
 
 type revision struct {
@@ -113,57 +113,57 @@ func Run(opts *Options) (int, error) {
 	cache := NewChunkCache()
 	var chunkList *ChunkList
 	var itemIndex int32
-	header := make([]string, 0, opts.HeaderLines)
+	// transformItem applies with-nth transformation to an item's raw data.
+	// It handles ANSI token propagation using prevLineAnsiState for cross-line continuity.
+	transformItem := func(item *Item, data []byte, transformer func([]Token, int32) string, index int32) {
+		tokens := Tokenize(byteString(data), opts.Delimiter)
+		if opts.Ansi && len(tokens) > 1 {
+			var ansiState *ansiState
+			if prevLineAnsiState != nil {
+				ansiStateDup := *prevLineAnsiState
+				ansiState = &ansiStateDup
+			}
+			for _, token := range tokens {
+				prevAnsiState := ansiState
+				_, _, ansiState = extractColor(token.text.ToString(), ansiState, nil)
+				if prevAnsiState != nil {
+					token.text.Prepend("\x1b[m" + prevAnsiState.ToString())
+				} else {
+					token.text.Prepend("\x1b[m")
+				}
+			}
+		}
+		transformed := transformer(tokens, index)
+		item.text, item.colors = ansiProcessor(stringBytes(transformed))
+
+		// We should not trim trailing whitespaces with background colors
+		var maxColorOffset int32
+		if item.colors != nil {
+			for _, ansi := range *item.colors {
+				if ansi.color.bg >= 0 {
+					maxColorOffset = max(maxColorOffset, ansi.offset[1])
+				}
+			}
+		}
+		item.text.TrimTrailingWhitespaces(int(maxColorOffset))
+	}
+
+	var nthTransformer func([]Token, int32) string
 	if opts.WithNth == nil {
 		chunkList = NewChunkList(cache, func(item *Item, data []byte) bool {
-			if len(header) < opts.HeaderLines {
-				header = append(header, byteString(data))
-				eventBox.Set(EvtHeader, header)
-				return false
-			}
 			item.text, item.colors = ansiProcessor(data)
 			item.text.Index = itemIndex
 			itemIndex++
 			return true
 		})
 	} else {
-		nthTransformer := opts.WithNth(opts.Delimiter)
+		nthTransformer = opts.WithNth(opts.Delimiter)
 		chunkList = NewChunkList(cache, func(item *Item, data []byte) bool {
-			tokens := Tokenize(byteString(data), opts.Delimiter)
+			if nthTransformer == nil {
-			if opts.Ansi && len(tokens) > 1 {
+				item.text, item.colors = ansiProcessor(data)
-				var ansiState *ansiState
+			} else {
-				if prevLineAnsiState != nil {
+				transformItem(item, data, nthTransformer, itemIndex)
-					ansiStateDup := *prevLineAnsiState
-					ansiState = &ansiStateDup
-				}
-				for _, token := range tokens {
-					prevAnsiState := ansiState
-					_, _, ansiState = extractColor(token.text.ToString(), ansiState, nil)
-					if prevAnsiState != nil {
-						token.text.Prepend("\x1b[m" + prevAnsiState.ToString())
-					} else {
-						token.text.Prepend("\x1b[m")
-					}
-				}
 			}
-			transformed := nthTransformer(tokens, itemIndex)
-			if len(header) < opts.HeaderLines {
-				header = append(header, transformed)
-				eventBox.Set(EvtHeader, header)
-				return false
-			}
-			item.text, item.colors = ansiProcessor(stringBytes(transformed))
-
-			// We should not trim trailing whitespaces with background colors
-			var maxColorOffset int32
-			if item.colors != nil {
-				for _, ansi := range *item.colors {
-					if ansi.color.bg >= 0 {
-						maxColorOffset = max(maxColorOffset, ansi.offset[1])
-					}
-				}
-			}
-			item.text.TrimTrailingWhitespaces(int(maxColorOffset))
 			item.text.Index = itemIndex
 			item.origText = &data
 			itemIndex++
@@ -193,7 +193,7 @@ func Run(opts *Options) (int, error) {
 	}
 
 	// Reader
-	streamingFilter := opts.Filter != nil && !sort && !opts.Tac && !opts.Sync
+	streamingFilter := opts.Filter != nil && !sort && !opts.Tac && !opts.Sync && opts.Bench == 0
 	var reader *Reader
 	if !streamingFilter {
 		reader = NewReader(func(data []byte) bool {
@@ -236,15 +236,17 @@ func Run(opts *Options) (int, error) {
 		denylist = make(map[int32]struct{})
 		denyMutex.Unlock()
 	}
+	headerLines := int32(opts.HeaderLines)
+	headerUpdated := false
 	patternBuilder := func(runes []rune) *Pattern {
 		denyMutex.Lock()
 		denylistCopy := maps.Clone(denylist)
 		denyMutex.Unlock()
 		return BuildPattern(cache, patternCache,
 			opts.Fuzzy, opts.FuzzyAlgo, opts.Extended, opts.Case, opts.Normalize, forward, withPos,
-			opts.Filter == nil, nth, opts.Delimiter, inputRevision, runes, denylistCopy)
+			opts.Filter == nil, nth, opts.Delimiter, inputRevision, runes, denylistCopy, headerLines)
 	}
-	matcher := NewMatcher(cache, patternBuilder, sort, opts.Tac, eventBox, inputRevision)
+	matcher := NewMatcher(cache, patternBuilder, sort, opts.Tac, eventBox, inputRevision, opts.Threads)
 
 	// Filtering mode
 	if opts.Filter != nil {
@@ -265,8 +267,11 @@ func Run(opts *Options) (int, error) {
 				func(runes []byte) bool {
 					item := Item{}
 					if chunkList.trans(&item, runes) {
+						if item.Index() < headerLines {
+							return false
+						}
 						mutex.Lock()
-						if result, _, _ := pattern.MatchItem(&item, false, slab); result != nil {
+						if result, _, _ := pattern.MatchItem(&item, false, slab); result.item != nil {
 							opts.Printer(transformer(&item))
 							found = true
 						}
@@ -281,6 +286,46 @@ func Run(opts *Options) (int, error) {
 
 			// NOTE: Streaming filter is inherently not compatible with --tail
 			snapshot, _, _ := chunkList.Snapshot(opts.Tail)
+
+			if opts.Bench > 0 {
+				// Benchmark mode: repeat scan for the given duration
+				totalItems := CountItems(snapshot)
+				var matchCount int
+				var times []time.Duration
+				deadline := time.Now().Add(opts.Bench)
+				for time.Now().Before(deadline) {
+					cache.Clear()
+					start := time.Now()
+					result := matcher.scan(MatchRequest{
+						chunks:  snapshot,
+						pattern: pattern})
+					times = append(times, time.Since(start))
+					matchCount = result.merger.Length()
+				}
+				// Print stats
+				var total time.Duration
+				minD, maxD := times[0], times[0]
+				for _, d := range times {
+					total += d
+					if d < minD {
+						minD = d
+					}
+					if d > maxD {
+						maxD = d
+					}
+				}
+				avg := total / time.Duration(len(times))
+				selectivity := float64(matchCount) / float64(totalItems) * 100
+				fmt.Printf("  %d iterations  avg: %.2fms  min: %.2fms  max: %.2fms  total: %.2fs  items: %d  matches: %d (%.2f%%)\n",
+					len(times),
+					float64(avg.Microseconds())/1000,
+					float64(minD.Microseconds())/1000,
+					float64(maxD.Microseconds())/1000,
+					total.Seconds(),
+					totalItems, matchCount, selectivity)
+				return ExitOk, nil
+			}
+
 			result := matcher.scan(MatchRequest{
 				chunks:  snapshot,
 				pattern: pattern})
@@ -330,10 +375,11 @@ func Run(opts *Options) (int, error) {
 	query := []rune{}
 	determine := func(final bool) {
 		if heightUnknown {
-			if total >= maxFit || final {
+			items := max(0, total-int(headerLines))
+			if items >= maxFit || final {
 				deferred = false
 				heightUnknown = false
-				terminal.startChan <- fitpad{min(total, maxFit), padHeight}
+				terminal.startChan <- fitpad{min(items, maxFit), padHeight}
 			}
 		} else if deferred {
 			deferred = false
@@ -349,11 +395,11 @@ func Run(opts *Options) (int, error) {
 			clearDenylist()
 		}
 		reading = true
+		headerUpdated = false
 		startTick = ticks
 		chunkList.Clear()
 		itemIndex = 0
 		inputRevision.bumpMajor()
-		header = make([]string, 0, opts.HeaderLines)
 		readyChan := make(chan bool)
 		go reader.restart(command, environ, readyChan)
 		<-readyChan
@@ -411,7 +457,11 @@ func Run(opts *Options) (int, error) {
 						snapshotRevision = inputRevision
 					}
 					total = count
-					terminal.UpdateCount(total, !reading, value.(*string))
+					terminal.UpdateCount(max(0, total-int(headerLines)), !reading, value.(*string))
+					if headerLines > 0 && !headerUpdated {
+						terminal.UpdateHeader(GetItems(snapshot, int(headerLines)))
+						headerUpdated = int32(total) >= headerLines
+					}
 					if heightUnknown && !deferred {
 						determine(!reading)
 					}
@@ -421,6 +471,8 @@ func Run(opts *Options) (int, error) {
 					var command *commandSpec
 					var environ []string
 					var changed bool
+					headerLinesChanged := false
+					withNthChanged := false
 					switch val := value.(type) {
 					case searchRequest:
 						sort = val.sort
@@ -441,6 +493,40 @@ func Run(opts *Options) (int, error) {
 							nth = *val.nth
 							bump = true
 						}
+						if val.headerLines != nil {
+							headerLines = int32(*val.headerLines)
+							headerUpdated = false
+							headerLinesChanged = true
+							bump = true
+						}
+						if val.withNth != nil {
+							newTransformer := val.withNth.fn
+							// Cancel any in-flight scan and block the terminal from reading
+							// items before mutating them in-place. Snapshot shares middle
+							// chunk pointers, so the matcher and terminal can race with us.
+							matcher.CancelScan()
+							terminal.PauseRendering()
+							// Reset cross-line ANSI state before re-processing all items
+							lineAnsiState = nil
+							prevLineAnsiState = nil
+							chunkList.ForEachItem(func(item *Item) {
+								origBytes := *item.origText
+								savedIndex := item.Index()
+								if newTransformer != nil {
+									transformItem(item, origBytes, newTransformer, savedIndex)
+								} else {
+									item.text, item.colors = ansiProcessor(origBytes)
+								}
+								item.text.Index = savedIndex
+								item.transformed = nil
+							}, func() {
+								nthTransformer = newTransformer
+							})
+							terminal.ResumeRendering()
+							matcher.ResumeScan()
+							withNthChanged = true
+							bump = true
+						}
 						if bump {
 							patternCache = make(map[string]*Pattern)
 							cache.Clear()
@@ -477,6 +563,16 @@ func Run(opts *Options) (int, error) {
 							snapshotRevision = inputRevision
 						}
 					}
+					if headerLinesChanged {
+						terminal.UpdateCount(max(0, total-int(headerLines)), !reading, nil)
+						if headerLines > 0 {
+							terminal.UpdateHeader(GetItems(snapshot, int(headerLines)))
+						} else {
+							terminal.UpdateHeader(nil)
+						}
+					} else if withNthChanged && headerLines > 0 {
+						terminal.UpdateHeader(GetItems(snapshot, int(headerLines)))
+					}
 					matcher.Reset(snapshot, input(), true, !reading, sort, snapshotRevision)
 					delay = false
 
@@ -486,11 +582,6 @@ func Run(opts *Options) (int, error) {
 						terminal.UpdateProgress(val)
 					}
 
-				case EvtHeader:
-					headerPadded := make([]string, opts.HeaderLines)
-					copy(headerPadded, value.([]string))
-					terminal.UpdateHeader(headerPadded)
-
 				case EvtSearchFin:
 					switch val := value.(type) {
 					case MatchResult:

src/matcher.go

@@ -3,7 +3,6 @@ package fzf
 import (
 	"fmt"
 	"runtime"
-	"sort"
 	"sync"
 	"time"
 
@@ -43,8 +42,11 @@ type Matcher struct {
 	reqBox         *util.EventBox
 	partitions     int
 	slab           []*util.Slab
+	sortBuf        [][]Result
 	mergerCache    map[string]MatchResult
 	revision       revision
+	scanMutex      sync.Mutex
+	cancelScan     *util.AtomicBool
 }
 
 const (
@@ -54,8 +56,11 @@ const (
 
 // NewMatcher returns a new Matcher
 func NewMatcher(cache *ChunkCache, patternBuilder func([]rune) *Pattern,
-	sort bool, tac bool, eventBox *util.EventBox, revision revision) *Matcher {
+	sort bool, tac bool, eventBox *util.EventBox, revision revision, threads int) *Matcher {
 	partitions := min(numPartitionsMultiplier*runtime.NumCPU(), maxPartitions)
+	if threads > 0 {
+		partitions = threads
+	}
 	return &Matcher{
 		cache:          cache,
 		patternBuilder: patternBuilder,
@@ -65,8 +70,10 @@ func NewMatcher(cache *ChunkCache, patternBuilder func([]rune) *Pattern,
 		reqBox:         util.NewEventBox(),
 		partitions:     partitions,
 		slab:           make([]*util.Slab, partitions),
+		sortBuf:        make([][]Result, partitions),
 		mergerCache:    make(map[string]MatchResult),
-		revision:       revision}
+		revision:       revision,
+		cancelScan:     util.NewAtomicBool(false)}
 }
 
 // Loop puts Matcher in action
@@ -126,7 +133,9 @@ func (m *Matcher) Loop() {
 		}
 
 		if result.merger == nil {
+			m.scanMutex.Lock()
 			result = m.scan(request)
+			m.scanMutex.Unlock()
 		}
 
 		if !result.cancelled {
@@ -174,7 +183,7 @@ func (m *Matcher) scan(request MatchRequest) MatchResult {
 		return MatchResult{m, m, false}
 	}
 	pattern := request.pattern
-	passMerger := PassMerger(&request.chunks, m.tac, request.revision)
+	passMerger := PassMerger(&request.chunks, m.tac, request.revision, pattern.startIndex)
 	if pattern.IsEmpty() {
 		return MatchResult{passMerger, passMerger, false}
 	}
@@ -212,11 +221,7 @@ func (m *Matcher) scan(request MatchRequest) MatchResult {
 				sliceMatches = append(sliceMatches, matches...)
 			}
 			if m.sort && request.pattern.sortable {
-				if m.tac {
+				m.sortBuf[idx] = radixSortResults(sliceMatches, m.tac, m.sortBuf[idx])
-					sort.Sort(ByRelevanceTac(sliceMatches))
-				} else {
-					sort.Sort(ByRelevance(sliceMatches))
-				}
 			}
 			resultChan <- partialResult{idx, sliceMatches}
 		}(idx, m.slab[idx], chunks)
@@ -238,7 +243,7 @@ func (m *Matcher) scan(request MatchRequest) MatchResult {
 			break
 		}
 
-		if m.reqBox.Peek(reqReset) {
+		if m.cancelScan.Get() || m.reqBox.Peek(reqReset) {
 			return MatchResult{nil, nil, wait()}
 		}
 
@@ -269,6 +274,20 @@ func (m *Matcher) Reset(chunks []*Chunk, patternRunes []rune, cancel bool, final
 	m.reqBox.Set(event, MatchRequest{chunks, pattern, final, sort, revision})
 }
 
+// CancelScan cancels any in-flight scan, waits for it to finish,
+// and prevents new scans from starting until ResumeScan is called.
+// This is used to safely mutate shared items (e.g., during with-nth changes).
+func (m *Matcher) CancelScan() {
+	m.cancelScan.Set(true)
+	m.scanMutex.Lock()
+	m.cancelScan.Set(false)
+}
+
+// ResumeScan allows scans to proceed again after CancelScan.
+func (m *Matcher) ResumeScan() {
+	m.scanMutex.Unlock()
+}
+
 func (m *Matcher) Stop() {
 	m.reqBox.Set(reqQuit, nil)
 }

src/merger.go

@@ -10,42 +10,46 @@ func EmptyMerger(revision revision) *Merger {
 // Merger holds a set of locally sorted lists of items and provides the view of
 // a single, globally-sorted list
 type Merger struct {
-	pattern  *Pattern
+	pattern    *Pattern
-	lists    [][]Result
+	lists      [][]Result
-	merged   []Result
+	merged     []Result
-	chunks   *[]*Chunk
+	chunks     *[]*Chunk
-	cursors  []int
+	cursors    []int
-	sorted   bool
+	sorted     bool
-	tac      bool
+	tac        bool
-	final    bool
+	final      bool
-	count    int
+	count      int
-	pass     bool
+	pass       bool
-	revision revision
+	startIndex int
-	minIndex int32
+	revision   revision
-	maxIndex int32
+	minIndex   int32
+	maxIndex   int32
 }
 
 // PassMerger returns a new Merger that simply returns the items in the
-// original order
+// original order. startIndex items are skipped from the beginning.
-func PassMerger(chunks *[]*Chunk, tac bool, revision revision) *Merger {
+func PassMerger(chunks *[]*Chunk, tac bool, revision revision, startIndex int32) *Merger {
 	var minIndex, maxIndex int32
 	if len(*chunks) > 0 {
 		minIndex = (*chunks)[0].items[0].Index()
 		maxIndex = (*chunks)[len(*chunks)-1].lastIndex(minIndex)
 	}
+	si := int(startIndex)
 	mg := Merger{
-		pattern:  nil,
+		pattern:    nil,
-		chunks:   chunks,
+		chunks:     chunks,
-		tac:      tac,
+		tac:        tac,
-		count:    0,
+		count:      0,
-		pass:     true,
+		pass:       true,
-		revision: revision,
+		startIndex: si,
-		minIndex: minIndex,
+		revision:   revision,
-		maxIndex: maxIndex}
+		minIndex:   minIndex + startIndex,
+		maxIndex:   maxIndex}
 
 	for _, chunk := range *mg.chunks {
 		mg.count += chunk.count
 	}
+	mg.count = max(0, mg.count-si)
 	return &mg
 }
 
@@ -113,6 +117,7 @@ func (mg *Merger) Get(idx int) Result {
 		if mg.tac {
 			idx = mg.count - idx - 1
 		}
+		idx += mg.startIndex
 		firstChunk := (*mg.chunks)[0]
 		if firstChunk.count < chunkSize && idx >= firstChunk.count {
 			idx -= firstChunk.count

src/options.go

@@ -8,6 +8,7 @@ import (
 	"regexp"
 	"strconv"
 	"strings"
+	"time"
 	"unicode"
 
 	"github.com/junegunn/fzf/src/algo"
@@ -587,6 +588,7 @@ type Options struct {
 	FreezeLeft        int
 	FreezeRight       int
 	WithNth           func(Delimiter) func([]Token, int32) string
+	WithNthExpr       string
 	AcceptNth         func(Delimiter) func([]Token, int32) string
 	Delimiter         Delimiter
 	Sort              int
@@ -677,6 +679,8 @@ type Options struct {
 	WalkerSkip        []string
 	Version           bool
 	Help              bool
+	Threads           int
+	Bench             time.Duration
 	CPUProfile        string
 	MEMProfile        string
 	BlockProfile      string
@@ -1626,7 +1630,7 @@ const (
 
 func init() {
 	executeRegexp = regexp.MustCompile(
-		`(?si)[:+](become|execute(?:-multi|-silent)?|reload(?:-sync)?|preview|(?:change|bg-transform|transform)-(?:query|prompt|(?:border|list|preview|input|header|footer)-label|header|footer|search|nth|pointer|ghost)|bg-transform|transform|change-(?:preview-window|preview|multi)|(?:re|un|toggle-)bind|pos|put|print|search|trigger)`)
+		`(?si)[:+](become|execute(?:-multi|-silent)?|reload(?:-sync)?|preview|(?:change|bg-transform|transform)-(?:query|prompt|(?:border|list|preview|input|header|footer)-label|header-lines|header|footer|search|with-nth|nth|pointer|ghost)|bg-transform|transform|change-(?:preview-window|preview|multi)|(?:re|un|toggle-)bind|pos|put|print|search|trigger)`)
 	splitRegexp = regexp.MustCompile("[,:]+")
 	actionNameRegexp = regexp.MustCompile("(?i)^[a-z-]+")
 }
@@ -2037,6 +2041,8 @@ func isExecuteAction(str string) actionType {
 		return actPreview
 	case "change-header":
 		return actChangeHeader
+	case "change-header-lines":
+		return actChangeHeaderLines
 	case "change-footer":
 		return actChangeFooter
 	case "change-list-label":
@@ -2067,6 +2073,8 @@ func isExecuteAction(str string) actionType {
 		return actChangeMulti
 	case "change-nth":
 		return actChangeNth
+	case "change-with-nth":
+		return actChangeWithNth
 	case "pos":
 		return actPosition
 	case "execute":
@@ -2097,10 +2105,14 @@ func isExecuteAction(str string) actionType {
 		return actTransformFooter
 	case "transform-header":
 		return actTransformHeader
+	case "transform-header-lines":
+		return actTransformHeaderLines
 	case "transform-ghost":
 		return actTransformGhost
 	case "transform-nth":
 		return actTransformNth
+	case "transform-with-nth":
+		return actTransformWithNth
 	case "transform-pointer":
 		return actTransformPointer
 	case "transform-prompt":
@@ -2127,10 +2139,14 @@ func isExecuteAction(str string) actionType {
 		return actBgTransformFooter
 	case "bg-transform-header":
 		return actBgTransformHeader
+	case "bg-transform-header-lines":
+		return actBgTransformHeaderLines
 	case "bg-transform-ghost":
 		return actBgTransformGhost
 	case "bg-transform-nth":
 		return actBgTransformNth
+	case "bg-transform-with-nth":
+		return actBgTransformWithNth
 	case "bg-transform-pointer":
 		return actBgTransformPointer
 	case "bg-transform-prompt":
@@ -2772,6 +2788,7 @@ func parseOptions(index *int, opts *Options, allArgs []string) error {
 			if opts.WithNth, err = nthTransformer(str); err != nil {
 				return err
 			}
+			opts.WithNthExpr = str
 		case "--accept-nth":
 			str, err := nextString("nth expression required")
 			if err != nil {
@@ -3367,6 +3384,23 @@ func parseOptions(index *int, opts *Options, allArgs []string) error {
 				return err
 			}
 			opts.WalkerSkip = filterNonEmpty(strings.Split(str, ","))
+		case "--threads":
+			if opts.Threads, err = nextInt("number of threads required"); err != nil {
+				return err
+			}
+			if opts.Threads < 0 {
+				return errors.New("--threads must be a positive integer")
+			}
+		case "--bench":
+			str, err := nextString("duration required (e.g. 3s, 500ms)")
+			if err != nil {
+				return err
+			}
+			dur, err := time.ParseDuration(str)
+			if err != nil {
+				return errors.New("invalid duration for --bench: " + str)
+			}
+			opts.Bench = dur
 		case "--profile-cpu":
 			if opts.CPUProfile, err = nextString("file path required: cpu"); err != nil {
 				return err

src/pattern.go

@@ -64,6 +64,9 @@ type Pattern struct {
 	procFun       map[termType]algo.Algo
 	cache         *ChunkCache
 	denylist      map[int32]struct{}
+	startIndex    int32
+	directAlgo    algo.Algo
+	directTerm    *term
 }
 
 var _splitRegex *regexp.Regexp
@@ -74,7 +77,7 @@ func init() {
 
 // BuildPattern builds Pattern object from the given arguments
 func BuildPattern(cache *ChunkCache, patternCache map[string]*Pattern, fuzzy bool, fuzzyAlgo algo.Algo, extended bool, caseMode Case, normalize bool, forward bool,
-	withPos bool, cacheable bool, nth []Range, delimiter Delimiter, revision revision, runes []rune, denylist map[int32]struct{}) *Pattern {
+	withPos bool, cacheable bool, nth []Range, delimiter Delimiter, revision revision, runes []rune, denylist map[int32]struct{}, startIndex int32) *Pattern {
 
 	var asString string
 	if extended {
@@ -146,9 +149,11 @@ func BuildPattern(cache *ChunkCache, patternCache map[string]*Pattern, fuzzy boo
 		delimiter:     delimiter,
 		cache:         cache,
 		denylist:      denylist,
+		startIndex:    startIndex,
 		procFun:       make(map[termType]algo.Algo)}
 
 	ptr.cacheKey = ptr.buildCacheKey()
+	ptr.directAlgo, ptr.directTerm = ptr.buildDirectAlgo(fuzzyAlgo)
 	ptr.procFun[termFuzzy] = fuzzyAlgo
 	ptr.procFun[termEqual] = algo.EqualMatch
 	ptr.procFun[termExact] = algo.ExactMatchNaive
@@ -272,6 +277,22 @@ func (p *Pattern) buildCacheKey() string {
 	return strings.Join(cacheableTerms, "\t")
 }
 
+// buildDirectAlgo returns the algo function and term for the direct fast path
+// in matchChunk. Returns (nil, nil) if the pattern is not suitable.
+// Requirements: extended mode, single term set with single non-inverse fuzzy term, no nth.
+func (p *Pattern) buildDirectAlgo(fuzzyAlgo algo.Algo) (algo.Algo, *term) {
+	if !p.extended || len(p.nth) > 0 {
+		return nil, nil
+	}
+	if len(p.termSets) == 1 && len(p.termSets[0]) == 1 {
+		t := &p.termSets[0][0]
+		if !t.inv && t.typ == termFuzzy {
+			return fuzzyAlgo, t
+		}
+	}
+	return nil, nil
+}
+
 // CacheKey is used to build string to be used as the key of result cache
 func (p *Pattern) CacheKey() string {
 	return p.cacheKey
@@ -301,18 +322,56 @@ func (p *Pattern) Match(chunk *Chunk, slab *util.Slab) []Result {
 func (p *Pattern) matchChunk(chunk *Chunk, space []Result, slab *util.Slab) []Result {
 	matches := []Result{}
 
-	if len(p.denylist) == 0 {
+	// Skip header items in chunks that contain them
-		// Huge code duplication for minimizing unnecessary map lookups
+	startIdx := 0
+	if p.startIndex > 0 && chunk.count > 0 && chunk.items[0].Index() < p.startIndex {
+		startIdx = int(p.startIndex - chunk.items[0].Index())
+		if startIdx >= chunk.count {
+			return matches
+		}
+	}
+
+	// Fast path: single fuzzy term, no nth, no denylist.
+	// Calls the algo function directly, bypassing MatchItem/extendedMatch/iter
+	// and avoiding per-match []Offset heap allocation.
+	if p.directAlgo != nil && len(p.denylist) == 0 {
+		t := p.directTerm
 		if space == nil {
-			for idx := 0; idx < chunk.count; idx++ {
+			for idx := startIdx; idx < chunk.count; idx++ {
-				if match, _, _ := p.MatchItem(&chunk.items[idx], p.withPos, slab); match != nil {
+				res, _ := p.directAlgo(t.caseSensitive, t.normalize, p.forward,
-					matches = append(matches, *match)
+					&chunk.items[idx].text, t.text, p.withPos, slab)
+				if res.Start >= 0 {
+					matches = append(matches, buildResultFromBounds(
+						&chunk.items[idx], res.Score,
+						int(res.Start), int(res.End), int(res.End), true))
 				}
 			}
 		} else {
 			for _, result := range space {
-				if match, _, _ := p.MatchItem(result.item, p.withPos, slab); match != nil {
+				res, _ := p.directAlgo(t.caseSensitive, t.normalize, p.forward,
-					matches = append(matches, *match)
+					&result.item.text, t.text, p.withPos, slab)
+				if res.Start >= 0 {
+					matches = append(matches, buildResultFromBounds(
+						result.item, res.Score,
+						int(res.Start), int(res.End), int(res.End), true))
+				}
+			}
+		}
+		return matches
+	}
+
+	if len(p.denylist) == 0 {
+		// Huge code duplication for minimizing unnecessary map lookups
+		if space == nil {
+			for idx := startIdx; idx < chunk.count; idx++ {
+				if match, _, _ := p.MatchItem(&chunk.items[idx], p.withPos, slab); match.item != nil {
+					matches = append(matches, match)
+				}
+			}
+		} else {
+			for _, result := range space {
+				if match, _, _ := p.MatchItem(result.item, p.withPos, slab); match.item != nil {
+					matches = append(matches, match)
 				}
 			}
 		}
@@ -320,12 +379,12 @@ func (p *Pattern) matchChunk(chunk *Chunk, space []Result, slab *util.Slab) []Re
 	}
 
 	if space == nil {
-		for idx := 0; idx < chunk.count; idx++ {
+		for idx := startIdx; idx < chunk.count; idx++ {
 			if _, prs := p.denylist[chunk.items[idx].Index()]; prs {
 				continue
 			}
-			if match, _, _ := p.MatchItem(&chunk.items[idx], p.withPos, slab); match != nil {
+			if match, _, _ := p.MatchItem(&chunk.items[idx], p.withPos, slab); match.item != nil {
-				matches = append(matches, *match)
+				matches = append(matches, match)
 			}
 		}
 	} else {
@@ -333,30 +392,29 @@ func (p *Pattern) matchChunk(chunk *Chunk, space []Result, slab *util.Slab) []Re
 			if _, prs := p.denylist[result.item.Index()]; prs {
 				continue
 			}
-			if match, _, _ := p.MatchItem(result.item, p.withPos, slab); match != nil {
+			if match, _, _ := p.MatchItem(result.item, p.withPos, slab); match.item != nil {
-				matches = append(matches, *match)
+				matches = append(matches, match)
 			}
 		}
 	}
 	return matches
 }
 
-// MatchItem returns true if the Item is a match
+// MatchItem returns the match result if the Item is a match.
-func (p *Pattern) MatchItem(item *Item, withPos bool, slab *util.Slab) (*Result, []Offset, *[]int) {
+// A zero-value Result (with item == nil) indicates no match.
+func (p *Pattern) MatchItem(item *Item, withPos bool, slab *util.Slab) (Result, []Offset, *[]int) {
 	if p.extended {
 		if offsets, bonus, pos := p.extendedMatch(item, withPos, slab); len(offsets) == len(p.termSets) {
-			result := buildResult(item, offsets, bonus)
+			return buildResult(item, offsets, bonus), offsets, pos
-			return &result, offsets, pos
 		}
-		return nil, nil, nil
+		return Result{}, nil, nil
 	}
 	offset, bonus, pos := p.basicMatch(item, withPos, slab)
 	if sidx := offset[0]; sidx >= 0 {
 		offsets := []Offset{offset}
-		result := buildResult(item, offsets, bonus)
+		return buildResult(item, offsets, bonus), offsets, pos
-		return &result, offsets, pos
 	}
-	return nil, nil, nil
+	return Result{}, nil, nil
 }
 
 func (p *Pattern) basicMatch(item *Item, withPos bool, slab *util.Slab) (Offset, int, *[]int) {

src/pattern_test.go

@@ -68,7 +68,7 @@ func buildPattern(fuzzy bool, fuzzyAlgo algo.Algo, extended bool, caseMode Case,
 	withPos bool, cacheable bool, nth []Range, delimiter Delimiter, runes []rune) *Pattern {
 	return BuildPattern(NewChunkCache(), make(map[string]*Pattern),
 		fuzzy, fuzzyAlgo, extended, caseMode, normalize, forward,
-		withPos, cacheable, nth, delimiter, revision{}, runes, nil)
+		withPos, cacheable, nth, delimiter, revision{}, runes, nil, 0)
 }
 
 func TestExact(t *testing.T) {

src/result.go

@@ -33,8 +33,6 @@ func buildResult(item *Item, offsets []Offset, score int) Result {
 		sort.Sort(ByOrder(offsets))
 	}
 
-	result := Result{item: item}
-	numChars := item.text.Length()
 	minBegin := math.MaxUint16
 	minEnd := math.MaxUint16
 	maxEnd := 0
@@ -49,6 +47,14 @@ func buildResult(item *Item, offsets []Offset, score int) Result {
 		}
 	}
 
+	return buildResultFromBounds(item, score, minBegin, minEnd, maxEnd, validOffsetFound)
+}
+
+// buildResultFromBounds builds a Result from pre-computed offset bounds.
+func buildResultFromBounds(item *Item, score int, minBegin, minEnd, maxEnd int, validOffsetFound bool) Result {
+	result := Result{item: item}
+	numChars := item.text.Length()
+
 	for idx, criterion := range sortCriteria {
 		val := uint16(math.MaxUint16)
 		switch criterion {
@@ -75,7 +81,6 @@ func buildResult(item *Item, offsets []Offset, score int) Result {
 			val = item.TrimLength()
 		case byPathname:
 			if validOffsetFound {
-				// lastDelim := strings.LastIndexByte(item.text.ToString(), '/')
 				lastDelim := -1
 				s := item.text.ToString()
 				for i := len(s) - 1; i >= 0; i-- {
@@ -123,7 +128,7 @@ func minRank() Result {
 	return Result{item: &minItem, points: [4]uint16{math.MaxUint16, 0, 0, 0}}
 }
 
-func (result *Result) colorOffsets(matchOffsets []Offset, nthOffsets []Offset, theme *tui.ColorTheme, colBase tui.ColorPair, colMatch tui.ColorPair, attrNth tui.Attr, hidden bool) []colorOffset {
+func (result *Result) colorOffsets(matchOffsets []Offset, nthOffsets []Offset, theme *tui.ColorTheme, colBase tui.ColorPair, colMatch tui.ColorPair, attrNth tui.Attr, nthOverlay tui.Attr, hidden bool) []colorOffset {
 	itemColors := result.item.Colors()
 
 	// No ANSI codes
@@ -208,6 +213,10 @@ func (result *Result) colorOffsets(matchOffsets []Offset, nthOffsets []Offset, t
 		}
 		return tui.NewColorPair(fg, bg, ansi.color.attr).WithUl(ansi.color.ul).MergeAttr(base)
 	}
+	fgAttr := tui.ColNormal.Attr()
+	nthAttrFinal := fgAttr.Merge(attrNth).Merge(nthOverlay)
+	nthBase := colBase.WithNewAttr(nthAttrFinal)
+
 	var colors []colorOffset
 	add := func(idx int) {
 		if curr.fbg >= 0 {
@@ -221,7 +230,7 @@ func (result *Result) colorOffsets(matchOffsets []Offset, nthOffsets []Offset, t
 			if curr.match {
 				var color tui.ColorPair
 				if curr.nth {
-					color = colBase.WithAttr(attrNth).Merge(colMatch)
+					color = nthBase.Merge(colMatch)
 				} else {
 					color = colBase.Merge(colMatch)
 				}
@@ -241,7 +250,7 @@ func (result *Result) colorOffsets(matchOffsets []Offset, nthOffsets []Offset, t
 					if color.Fg().IsDefault() && origColor.HasBg() {
 						color = origColor
 						if curr.nth {
-							color = color.WithAttr(attrNth &^ tui.AttrRegular)
+							color = color.WithAttr((attrNth &^ tui.AttrRegular).Merge(nthOverlay))
 						}
 					} else {
 						color = origColor.MergeNonDefault(color)
@@ -253,7 +262,7 @@ func (result *Result) colorOffsets(matchOffsets []Offset, nthOffsets []Offset, t
 				ansi := itemColors[curr.index]
 				base := colBase
 				if curr.nth {
-					base = base.WithAttr(attrNth)
+					base = nthBase
 				}
 				if hidden {
 					base = base.WithFg(theme.Nomatch)
@@ -265,7 +274,7 @@ func (result *Result) colorOffsets(matchOffsets []Offset, nthOffsets []Offset, t
 					match:  false,
 					url:    ansi.color.url})
 			} else {
-				color := colBase.WithAttr(attrNth)
+				color := nthBase
 				if hidden {
 					color = color.WithFg(theme.Nomatch)
 				}
@@ -334,3 +343,79 @@ func (a ByRelevanceTac) Swap(i, j int) {
 func (a ByRelevanceTac) Less(i, j int) bool {
 	return compareRanks(a[i], a[j], true)
 }
+
+// radixSortResults sorts Results by their points key using LSD radix sort.
+// O(n) time complexity vs O(n log n) for comparison sort.
+// The sort is stable, so equal-key items maintain original (item-index) order.
+// For tac mode, runs of equal keys are reversed after sorting.
+func radixSortResults(a []Result, tac bool, scratch []Result) []Result {
+	n := len(a)
+	if n < 128 {
+		if tac {
+			sort.Sort(ByRelevanceTac(a))
+		} else {
+			sort.Sort(ByRelevance(a))
+		}
+		return scratch[:0]
+	}
+
+	if cap(scratch) < n {
+		scratch = make([]Result, n)
+	}
+	buf := scratch[:n]
+	src, dst := a, buf
+	scattered := 0
+
+	for pass := range 8 {
+		shift := uint(pass) * 8
+
+		var count [256]int
+		for i := range src {
+			count[byte(sortKey(&src[i])>>shift)]++
+		}
+
+		// Skip if all items have the same byte value at this position
+		if count[byte(sortKey(&src[0])>>shift)] == n {
+			continue
+		}
+
+		var offset [256]int
+		for i := 1; i < 256; i++ {
+			offset[i] = offset[i-1] + count[i-1]
+		}
+
+		for i := range src {
+			b := byte(sortKey(&src[i]) >> shift)
+			dst[offset[b]] = src[i]
+			offset[b]++
+		}
+
+		src, dst = dst, src
+		scattered++
+	}
+
+	// If odd number of scatters, data is in buf, copy back to a
+	if scattered%2 == 1 {
+		copy(a, src)
+	}
+
+	// Handle tac: reverse runs of equal keys so equal-key items
+	// are in reverse item-index order
+	if tac {
+		i := 0
+		for i < n {
+			ki := sortKey(&a[i])
+			j := i + 1
+			for j < n && sortKey(&a[j]) == ki {
+				j++
+			}
+			if j-i > 1 {
+				for l, r := i, j-1; l < r; l, r = l+1, r-1 {
+					a[l], a[r] = a[r], a[l]
+				}
+			}
+			i = j
+		}
+	}
+	return scratch
+}

src/result_others.go

@@ -1,4 +1,4 @@
-//go:build !386 && !amd64
+//go:build !386 && !amd64 && !arm64
 
 package fzf
 
@@ -14,3 +14,7 @@ func compareRanks(irank Result, jrank Result, tac bool) bool {
 	}
 	return (irank.item.Index() <= jrank.item.Index()) != tac
 }
+
+func sortKey(r *Result) uint64 {
+	return uint64(r.points[0]) | uint64(r.points[1])<<16 | uint64(r.points[2])<<32 | uint64(r.points[3])<<48
+}

src/result_test.go

@@ -2,6 +2,7 @@ package fzf
 
 import (
 	"math"
+	"math/rand"
 	"sort"
 	"testing"
 
@@ -131,7 +132,7 @@ func TestColorOffset(t *testing.T) {
 
 	colBase := tui.NewColorPair(89, 189, tui.AttrUndefined)
 	colMatch := tui.NewColorPair(99, 199, tui.AttrUndefined)
-	colors := item.colorOffsets(offsets, nil, tui.Dark256, colBase, colMatch, tui.AttrUndefined, false)
+	colors := item.colorOffsets(offsets, nil, tui.Dark256, colBase, colMatch, tui.AttrUndefined, 0, false)
 	assert := func(idx int, b int32, e int32, c tui.ColorPair) {
 		o := colors[idx]
 		if o.offset[0] != b || o.offset[1] != e || o.color != c {
@@ -158,7 +159,7 @@ func TestColorOffset(t *testing.T) {
 
 	nthOffsets := []Offset{{37, 39}, {42, 45}}
 	for _, attr := range []tui.Attr{tui.AttrRegular, tui.StrikeThrough} {
-		colors = item.colorOffsets(offsets, nthOffsets, tui.Dark256, colRegular, colUnderline, attr, false)
+		colors = item.colorOffsets(offsets, nthOffsets, tui.Dark256, colRegular, colUnderline, attr, 0, false)
 
 		// [{[0 5] {1 5 0}} {[5 15] {1 5 8}} {[15 20] {1 5 0}}
 		//  {[22 25] {2 6 1}} {[25 27] {2 6 9}} {[27 30] {-1 -1 8}}
@@ -181,4 +182,92 @@ func TestColorOffset(t *testing.T) {
 		assert(10, 37, 39, tui.NewColorPair(4, 8, expected))
 		assert(11, 39, 40, tui.NewColorPair(4, 8, tui.Bold))
 	}
+
+	// Test nthOverlay: simulates nth:regular with current-fg:underline
+	// The overlay (underline) should survive even though nth:regular clears attrs.
+	// Precedence: fg < nth < current-fg
+	colors = item.colorOffsets(offsets, nthOffsets, tui.Dark256, colRegular, colUnderline, tui.AttrRegular, tui.Underline, false)
+
+	// nth regions should have Underline (from overlay), not cleared by AttrRegular
+	// Non-nth regions keep colBase attrs (AttrUndefined)
+	assert(0, 0, 5, tui.NewColorPair(1, 5, tui.AttrUndefined))
+	assert(1, 5, 15, tui.NewColorPair(1, 5, tui.Underline))
+	assert(2, 15, 20, tui.NewColorPair(1, 5, tui.AttrUndefined))
+	assert(3, 22, 25, tui.NewColorPair(2, 6, tui.Bold))
+	assert(4, 25, 27, tui.NewColorPair(2, 6, tui.Bold|tui.Underline))
+	assert(5, 27, 30, colUnderline)
+	assert(6, 30, 32, tui.NewColorPair(3, 7, tui.Underline))
+	assert(7, 32, 33, colUnderline)
+	assert(8, 33, 35, tui.NewColorPair(4, 8, tui.Bold|tui.Underline))
+	assert(9, 35, 37, tui.NewColorPair(4, 8, tui.Bold))
+	// nth region within ANSI bold: AttrRegular clears, overlay adds Underline back
+	assert(10, 37, 39, tui.NewColorPair(4, 8, tui.Bold|tui.Underline))
+	assert(11, 39, 40, tui.NewColorPair(4, 8, tui.Bold))
+
+	// Test nthOverlay with additive attrs: nth:strikethrough with selected-fg:bold
+	colors = item.colorOffsets(offsets, nthOffsets, tui.Dark256, colRegular, colUnderline, tui.StrikeThrough, tui.Bold, false)
+
+	// Non-nth entries unchanged from overlay=0 case
+	assert(0, 0, 5, tui.NewColorPair(1, 5, tui.AttrUndefined))
+	assert(5, 27, 30, colUnderline) // match only, no nth
+	assert(7, 32, 33, colUnderline) // match only, no nth
+	// nth region within ANSI bold: StrikeThrough|Bold merged with ANSI Bold
+	assert(10, 37, 39, tui.NewColorPair(4, 8, tui.Bold|tui.StrikeThrough))
+}
+
+func TestRadixSortResults(t *testing.T) {
+	sortCriteria = []criterion{byScore, byLength}
+
+	rng := rand.New(rand.NewSource(42))
+
+	for _, n := range []int{128, 256, 500, 1000} {
+		for _, tac := range []bool{false, true} {
+			// Build items with random points and indices
+			items := make([]*Item, n)
+			for i := range items {
+				items[i] = &Item{text: util.Chars{Index: int32(i)}}
+			}
+
+			results := make([]Result, n)
+			for i := range results {
+				results[i] = Result{
+					item: items[i],
+					points: [4]uint16{
+						uint16(rng.Intn(256)),
+						uint16(rng.Intn(256)),
+						uint16(rng.Intn(256)),
+						uint16(rng.Intn(256)),
+					},
+				}
+			}
+
+			// Make some duplicates to test stability
+			for i := 0; i < n/4; i++ {
+				j := rng.Intn(n)
+				k := rng.Intn(n)
+				results[j].points = results[k].points
+			}
+
+			// Copy for reference sort
+			expected := make([]Result, n)
+			copy(expected, results)
+			if tac {
+				sort.Sort(ByRelevanceTac(expected))
+			} else {
+				sort.Sort(ByRelevance(expected))
+			}
+
+			// Radix sort
+			var scratch []Result
+			scratch = radixSortResults(results, tac, scratch)
+
+			for i := range results {
+				if results[i] != expected[i] {
+					t.Errorf("n=%d tac=%v: mismatch at index %d: got item %d, want item %d",
+						n, tac, i, results[i].item.Index(), expected[i].item.Index())
+					break
+				}
+			}
+		}
+	}
 }

src/result_x86.go

@@ -1,4 +1,4 @@
-//go:build 386 || amd64
+//go:build 386 || amd64 || arm64
 
 package fzf
 
@@ -14,3 +14,7 @@ func compareRanks(irank Result, jrank Result, tac bool) bool {
 	}
 	return (irank.item.Index() <= jrank.item.Index()) != tac
 }
+
+func sortKey(r *Result) uint64 {
+	return *(*uint64)(unsafe.Pointer(&r.points[0]))
+}

src/terminal.go

@@ -314,6 +314,7 @@ type Terminal struct {
 	sort                 bool
 	toggleSort           bool
 	track                trackOption
+	targetIndex          int32
 	delimiter            Delimiter
 	expect               map[tui.Event]string
 	keymap               map[tui.Event][]*action
@@ -327,7 +328,7 @@ type Terminal struct {
 	headerVisible        bool
 	headerFirst          bool
 	headerLines          int
-	header               []string
+	header               []Item
 	header0              []string
 	footer               []string
 	ellipsis             string
@@ -339,6 +340,9 @@ type Terminal struct {
 	nthAttr              tui.Attr
 	nth                  []Range
 	nthCurrent           []Range
+	withNthDefault       string
+	withNthExpr          string
+	withNthEnabled       bool
 	acceptNth            func([]Token, int32) string
 	tabstop              int
 	margin               [4]sizeSpec
@@ -383,6 +387,7 @@ type Terminal struct {
 	hasLoadActions       bool
 	hasResizeActions     bool
 	triggerLoad          bool
+	filterSelection      bool
 	reading              bool
 	running              *util.AtomicBool
 	failed               *string
@@ -542,6 +547,7 @@ const (
 	actChangeBorderLabel
 	actChangeGhost
 	actChangeHeader
+	actChangeHeaderLines
 	actChangeFooter
 	actChangeHeaderLabel
 	actChangeFooterLabel
@@ -549,6 +555,7 @@ const (
 	actChangeListLabel
 	actChangeMulti
 	actChangeNth
+	actChangeWithNth
 	actChangePointer
 	actChangePreview
 	actChangePreviewLabel
@@ -627,12 +634,14 @@ const (
 	actTransformBorderLabel
 	actTransformGhost
 	actTransformHeader
+	actTransformHeaderLines
 	actTransformFooter
 	actTransformHeaderLabel
 	actTransformFooterLabel
 	actTransformInputLabel
 	actTransformListLabel
 	actTransformNth
+	actTransformWithNth
 	actTransformPointer
 	actTransformPreviewLabel
 	actTransformPrompt
@@ -645,12 +654,14 @@ const (
 	actBgTransformBorderLabel
 	actBgTransformGhost
 	actBgTransformHeader
+	actBgTransformHeaderLines
 	actBgTransformFooter
 	actBgTransformHeaderLabel
 	actBgTransformFooterLabel
 	actBgTransformInputLabel
 	actBgTransformListLabel
 	actBgTransformNth
+	actBgTransformWithNth
 	actBgTransformPointer
 	actBgTransformPreviewLabel
 	actBgTransformPrompt
@@ -710,12 +721,14 @@ func processExecution(action actionType) bool {
 		actTransformBorderLabel,
 		actTransformGhost,
 		actTransformHeader,
+		actTransformHeaderLines,
 		actTransformFooter,
 		actTransformHeaderLabel,
 		actTransformFooterLabel,
 		actTransformInputLabel,
 		actTransformListLabel,
 		actTransformNth,
+		actTransformWithNth,
 		actTransformPointer,
 		actTransformPreviewLabel,
 		actTransformPrompt,
@@ -725,12 +738,14 @@ func processExecution(action actionType) bool {
 		actBgTransformBorderLabel,
 		actBgTransformGhost,
 		actBgTransformHeader,
+		actBgTransformHeaderLines,
 		actBgTransformFooter,
 		actBgTransformHeaderLabel,
 		actBgTransformFooterLabel,
 		actBgTransformInputLabel,
 		actBgTransformListLabel,
 		actBgTransformNth,
+		actBgTransformWithNth,
 		actBgTransformPointer,
 		actBgTransformPreviewLabel,
 		actBgTransformPrompt,
@@ -760,15 +775,21 @@ type placeholderFlags struct {
 	raw           bool
 }
 
+type withNthSpec struct {
+	fn func([]Token, int32) string // nil = clear (restore original)
+}
+
 type searchRequest struct {
-	sort     bool
+	sort        bool
-	sync     bool
+	sync        bool
-	nth      *[]Range
+	nth         *[]Range
-	command  *commandSpec
+	withNth     *withNthSpec
-	environ  []string
+	headerLines *int
-	changed  bool
+	command     *commandSpec
-	denylist []int32
+	environ     []string
-	revision revision
+	changed     bool
+	denylist    []int32
+	revision    revision
 }
 
 type previewRequest struct {
@@ -1022,6 +1043,7 @@ func NewTerminal(opts *Options, eventBox *util.EventBox, executor *util.Executor
 		sort:               opts.Sort > 0,
 		toggleSort:         opts.ToggleSort,
 		track:              opts.Track,
+		targetIndex:        minItem.Index(),
 		delimiter:          opts.Delimiter,
 		expect:             opts.Expect,
 		keymap:             opts.Keymap,
@@ -1063,7 +1085,7 @@ func NewTerminal(opts *Options, eventBox *util.EventBox, executor *util.Executor
 		headerFirst:        opts.HeaderFirst,
 		headerLines:        opts.HeaderLines,
 		gap:                opts.Gap,
-		header:             []string{},
+		header:             []Item{},
 		footer:             opts.Footer,
 		header0:            opts.Header,
 		ansi:               opts.Ansi,
@@ -1072,6 +1094,9 @@ func NewTerminal(opts *Options, eventBox *util.EventBox, executor *util.Executor
 		nthAttr:            opts.Theme.Nth.Attr,
 		nth:                opts.Nth,
 		nthCurrent:         opts.Nth,
+		withNthDefault:     opts.WithNthExpr,
+		withNthExpr:        opts.WithNthExpr,
+		withNthEnabled:     opts.WithNth != nil,
 		tabstop:            opts.Tabstop,
 		raw:                opts.Raw,
 		hasStartActions:    false,
@@ -1343,6 +1368,9 @@ func (t *Terminal) environImpl(forPreview bool) []string {
 	if len(t.nthCurrent) > 0 {
 		env = append(env, "FZF_NTH="+RangesToString(t.nthCurrent))
 	}
+	if len(t.withNthExpr) > 0 {
+		env = append(env, "FZF_WITH_NTH="+t.withNthExpr)
+	}
 	if t.raw {
 		val := "0"
 		if t.isCurrentItemMatch() {
@@ -1526,7 +1554,7 @@ func (t *Terminal) ansiLabelPrinter(str string, color *tui.ColorPair, fill bool)
 	printFn := func(window tui.Window, limit int) {
 		if offsets == nil {
 			// tui.Col* are not initialized until renderer.Init()
-			offsets = result.colorOffsets(nil, nil, t.theme, *color, *color, t.nthAttr, false)
+			offsets = result.colorOffsets(nil, nil, t.theme, *color, *color, t.nthAttr, 0, false)
 		}
 		for limit > 0 {
 			if length > limit {
@@ -1589,7 +1617,7 @@ func (t *Terminal) parsePrompt(prompt string) (func(), int) {
 				return 1
 			}
 			t.printHighlighted(
-				Result{item: item}, tui.ColPrompt, tui.ColPrompt, false, false, false, line, line, true, preTask, nil)
+				Result{item: item}, tui.ColPrompt, tui.ColPrompt, false, false, false, line, line, true, preTask, nil, 0)
 		})
 		t.wrap = wrap
 	}
@@ -1712,6 +1740,17 @@ func (t *Terminal) Input() (bool, []rune) {
 	return paused, copySlice(src)
 }
 
+// PauseRendering blocks the terminal from reading items.
+// Must be paired with ResumeRendering.
+func (t *Terminal) PauseRendering() {
+	t.mutex.Lock()
+}
+
+// ResumeRendering releases the lock acquired by PauseRendering.
+func (t *Terminal) ResumeRendering() {
+	t.mutex.Unlock()
+}
+
 // UpdateCount updates the count information
 func (t *Terminal) UpdateCount(cnt int, final bool, failedCommand *string) {
 	t.mutex.Lock()
@@ -1755,8 +1794,14 @@ func (t *Terminal) changeFooter(footer string) {
 }
 
 // UpdateHeader updates the header
-func (t *Terminal) UpdateHeader(header []string) {
+func (t *Terminal) UpdateHeader(header []Item) {
 	t.mutex.Lock()
+	// Pad to t.headerLines so that click coordinate mapping works correctly
+	if len(header) < t.headerLines {
+		padded := make([]Item, t.headerLines)
+		copy(padded, header)
+		header = padded
+	}
 	t.header = header
 	t.mutex.Unlock()
 	t.reqBox.Set(reqHeader, nil)
@@ -1788,6 +1833,10 @@ func (t *Terminal) UpdateList(result MatchResult) {
 			prevIndex = merger.First().item.Index()
 		}
 	}
+	if t.targetIndex != minItem.Index() {
+		prevIndex = t.targetIndex
+		t.targetIndex = minItem.Index()
+	}
 	t.progress = 100
 	t.merger = merger
 	t.resultMerger = merger
@@ -1824,6 +1873,21 @@ func (t *Terminal) UpdateList(result MatchResult) {
 		}
 		t.revision = newRevision
 		t.version++
+
+		// Filter out selections that no longer match after with-nth change.
+		// Must be inside the revision check so we don't consume the flag
+		// on a stale EvtSearchFin from a previous search.
+		if t.filterSelection && t.multi > 0 && len(t.selected) > 0 {
+			matchMap := t.resultMerger.ToMap()
+			filtered := make(map[int32]selectedItem)
+			for k, v := range t.selected {
+				if _, matched := matchMap[k]; matched {
+					filtered[k] = v
+				}
+			}
+			t.selected = filtered
+		}
+		t.filterSelection = false
 	}
 	if t.triggerLoad {
 		t.triggerLoad = false
@@ -3079,11 +3143,11 @@ func (t *Terminal) printHeader() {
 	}
 
 	t.withWindow(t.headerWindow, func() {
-		var lines []string
+		var headerItems []Item
 		if !t.hasHeaderLinesWindow() {
-			lines = t.header
+			headerItems = t.header
 		}
-		t.printHeaderImpl(t.headerWindow, t.headerBorderShape, t.header0, lines)
+		t.printHeaderImpl(t.headerWindow, t.headerBorderShape, t.header0, headerItems)
 	})
 	if w, shape := t.determineHeaderLinesShape(); w {
 		t.withWindow(t.headerLinesWindow, func() {
@@ -3121,7 +3185,7 @@ func (t *Terminal) printFooter() {
 				func(markerClass) int {
 					t.footerWindow.Print(indent)
 					return indentSize
-				}, nil)
+				}, nil, 0)
 		}
 	})
 	t.wrap = wrap
@@ -3145,7 +3209,7 @@ func (t *Terminal) headerIndentImpl(base int, borderShape tui.BorderShape) int {
 	return indentSize
 }
 
-func (t *Terminal) printHeaderImpl(window tui.Window, borderShape tui.BorderShape, lines1 []string, lines2 []string) {
+func (t *Terminal) printHeaderImpl(window tui.Window, borderShape tui.BorderShape, lines1 []string, lines2 []Item) {
 	max := t.window.Height()
 	if !t.inputless && t.inputWindow == nil && window == nil && t.headerFirst {
 		max--
@@ -3172,7 +3236,8 @@ func (t *Terminal) printHeaderImpl(window tui.Window, borderShape tui.BorderShap
 	}
 	indent := strings.Repeat(" ", indentSize)
 	t.wrap = false
-	for idx, lineStr := range append(append([]string{}, lines1...), lines2...) {
+	totalLines := len(lines1) + len(lines2)
+	for idx := 0; idx < totalLines; idx++ {
 		line := idx
 		if needReverse && idx < len(lines1) {
 			line = len(lines1) - idx - 1
@@ -3186,18 +3251,25 @@ func (t *Terminal) printHeaderImpl(window tui.Window, borderShape tui.BorderShap
 		if line >= max {
 			continue
 		}
-		trimmed, colors, newState := extractColor(lineStr, state, nil)
+
-		state = newState
+		var item *Item
-		item := &Item{
+		if idx < len(lines1) {
-			text:   util.ToChars([]byte(trimmed)),
+			trimmed, colors, newState := extractColor(lines1[idx], state, nil)
-			colors: colors}
+			state = newState
+			item = &Item{
+				text:   util.ToChars([]byte(trimmed)),
+				colors: colors}
+		} else {
+			headerItem := lines2[idx-len(lines1)]
+			item = &headerItem
+		}
 
 		t.printHighlighted(Result{item: item},
 			tui.ColHeader, tui.ColHeader, false, false, false, line, line, true,
 			func(markerClass) int {
 				t.window.Print(indent)
 				return indentSize
-			}, nil)
+			}, nil, 0)
 	}
 	t.wrap = wrap
 }
@@ -3435,7 +3507,14 @@ func (t *Terminal) printItem(result Result, line int, maxLine int, index int, cu
 			}
 			return indentSize
 		}
-		finalLineNum = t.printHighlighted(result, tui.ColCurrent, tui.ColCurrentMatch, true, true, !matched, line, maxLine, forceRedraw, preTask, postTask)
+		colCurrent := tui.ColCurrent
+		nthOverlay := t.theme.NthCurrentAttr
+		if selected {
+			nthOverlay = t.theme.NthSelectedAttr.Merge(t.theme.NthCurrentAttr)
+			baseAttr := tui.ColNormal.Attr().Merge(t.theme.NthSelectedAttr).Merge(t.theme.NthCurrentAttr)
+			colCurrent = colCurrent.WithNewAttr(baseAttr)
+		}
+		finalLineNum = t.printHighlighted(result, colCurrent, tui.ColCurrentMatch, true, true, !matched, line, maxLine, forceRedraw, preTask, postTask, nthOverlay)
 	} else {
 		preTask := func(marker markerClass) int {
 			w := t.window.Width() - t.pointerLen
@@ -3469,7 +3548,11 @@ func (t *Terminal) printItem(result Result, line int, maxLine int, index int, cu
 			base = base.WithBg(altBg)
 			match = match.WithBg(altBg)
 		}
-		finalLineNum = t.printHighlighted(result, base, match, false, true, !matched, line, maxLine, forceRedraw, preTask, postTask)
+		var nthOverlay tui.Attr
+		if selected {
+			nthOverlay = t.theme.NthSelectedAttr
+		}
+		finalLineNum = t.printHighlighted(result, base, match, false, true, !matched, line, maxLine, forceRedraw, preTask, postTask, nthOverlay)
 	}
 	for i := 0; i < t.gap && finalLineNum < maxLine; i++ {
 		finalLineNum++
@@ -3570,7 +3653,7 @@ func (t *Terminal) overflow(runes []rune, max int) bool {
 	return t.displayWidthWithLimit(runes, 0, max) > max
 }
 
-func (t *Terminal) printHighlighted(result Result, colBase tui.ColorPair, colMatch tui.ColorPair, current bool, match bool, hidden bool, lineNum int, maxLineNum int, forceRedraw bool, preTask func(markerClass) int, postTask func(int, int, bool, bool, tui.ColorPair)) int {
+func (t *Terminal) printHighlighted(result Result, colBase tui.ColorPair, colMatch tui.ColorPair, current bool, match bool, hidden bool, lineNum int, maxLineNum int, forceRedraw bool, preTask func(markerClass) int, postTask func(int, int, bool, bool, tui.ColorPair), nthOverlay tui.Attr) int {
 	var displayWidth int
 	item := result.item
 	matchOffsets := []Offset{}
@@ -3611,7 +3694,9 @@ func (t *Terminal) printHighlighted(result Result, colBase tui.ColorPair, colMat
 			// But if 'nth' is set to 'regular', it's a sign that you're applying
 			// a different style to the rest of the string. e.g. 'nth:regular,fg:dim'
 			// In this case, we still need to apply it to clear the style.
-			colBase = colBase.WithAttr(t.nthAttr)
+			fgAttr := tui.ColNormal.Attr()
+			nthAttrFinal := fgAttr.Merge(t.nthAttr).Merge(nthOverlay)
+			colBase = colBase.WithNewAttr(nthAttrFinal)
 		}
 		if !wholeCovered && t.nthAttr > 0 {
 			var tokens []Token
@@ -3630,7 +3715,7 @@ func (t *Terminal) printHighlighted(result Result, colBase tui.ColorPair, colMat
 			sort.Sort(ByOrder(nthOffsets))
 		}
 	}
-	allOffsets := result.colorOffsets(charOffsets, nthOffsets, t.theme, colBase, colMatch, t.nthAttr, hidden)
+	allOffsets := result.colorOffsets(charOffsets, nthOffsets, t.theme, colBase, colMatch, t.nthAttr, nthOverlay, hidden)
 
 	// Determine split offset for horizontal scrolling with freeze
 	splitOffset1 := -1
@@ -5288,9 +5373,13 @@ func (t *Terminal) addClickHeaderWord(env []string) []string {
 		return env
 	}
 
-	// NOTE: t.header is padded with empty strings so that its size is equal to t.headerLines
 	nthBase := 0
-	headers := [2][]string{t.header, t.header0}
+	// Convert header items to strings for click handling
+	headerStrs := make([]string, len(t.header))
+	for i, item := range t.header {
+		headerStrs[i] = item.text.ToString()
+	}
+	headers := [2][]string{headerStrs, t.header0}
 	if t.layout == layoutReverse {
 		headers[0], headers[1] = headers[1], headers[0]
 	}
@@ -5892,6 +5981,8 @@ func (t *Terminal) Loop() error {
 	events := []util.EventType{}
 	changed := false
 	var newNth *[]Range
+	var newWithNth *withNthSpec
+	var newHeaderLines *int
 	req := func(evts ...util.EventType) {
 		for _, event := range evts {
 			events = append(events, event)
@@ -5908,6 +5999,8 @@ func (t *Terminal) Loop() error {
 		events = []util.EventType{}
 		changed = false
 		newNth = nil
+		newWithNth = nil
+		newHeaderLines = nil
 		beof := false
 		queryChanged := false
 		denylist := []int32{}
@@ -6247,6 +6340,23 @@ func (t *Terminal) Loop() error {
 				}
 			case actPrintQuery:
 				req(reqPrintQuery)
+			case actChangeHeaderLines, actTransformHeaderLines, actBgTransformHeaderLines:
+				capture(true, func(expr string) {
+					if n, err := strconv.Atoi(expr); err == nil && n >= 0 && n != t.headerLines {
+						t.headerLines = n
+						newHeaderLines = &n
+						changed = true
+						// Deselect items that are now part of the header
+						for idx := range t.selected {
+							if idx < int32(n) {
+								delete(t.selected, idx)
+							}
+						}
+						// Tell UpdateList to reposition cursor to the current item
+						t.targetIndex = t.currentIndex()
+						req(reqList, reqPrompt, reqInfo, reqHeader)
+					}
+				})
 			case actChangeMulti:
 				multi := t.multi
 				if a.a == "" {
@@ -6281,6 +6391,33 @@ func (t *Terminal) Loop() error {
 						t.forceRerenderList()
 					}
 				})
+			case actChangeWithNth, actTransformWithNth, actBgTransformWithNth:
+				if !t.withNthEnabled {
+					break Action
+				}
+				capture(true, func(expr string) {
+					tokens := strings.Split(expr, "|")
+					withNthExpr := tokens[0]
+					if len(tokens) > 1 {
+						a.a = strings.Join(append(tokens[1:], tokens[0]), "|")
+					}
+					// Empty value restores the default --with-nth
+					if len(withNthExpr) == 0 {
+						withNthExpr = t.withNthDefault
+					}
+					if withNthExpr != t.withNthExpr {
+						if factory, err := nthTransformer(withNthExpr); err == nil {
+							newWithNth = &withNthSpec{fn: factory(t.delimiter)}
+						} else {
+							return
+						}
+						t.withNthExpr = withNthExpr
+						t.filterSelection = true
+						changed = true
+						t.clearNumLinesCache()
+						t.forceRerenderList()
+					}
+				})
 			case actChangeQuery:
 				t.input = []rune(a.a)
 				t.cx = len(t.input)
@@ -7428,7 +7565,7 @@ func (t *Terminal) Loop() error {
 		reload := changed || newCommand != nil
 		var reloadRequest *searchRequest
 		if reload {
-			reloadRequest = &searchRequest{sort: t.sort, sync: reloadSync, nth: newNth, command: newCommand, environ: t.environ(), changed: changed, denylist: denylist, revision: t.resultMerger.Revision()}
+			reloadRequest = &searchRequest{sort: t.sort, sync: reloadSync, nth: newNth, withNth: newWithNth, headerLines: newHeaderLines, command: newCommand, environ: t.environ(), changed: changed, denylist: denylist, revision: t.resultMerger.Revision()}
 		}
 
 		// Dispatch queued background requests

src/tui/tui.go

@@ -447,6 +447,12 @@ func (p ColorPair) WithAttr(attr Attr) ColorPair {
 	return dup
 }
 
+func (p ColorPair) WithNewAttr(attr Attr) ColorPair {
+	dup := p
+	dup.attr = attr
+	return dup
+}
+
 func (p ColorPair) WithFg(fg ColorAttr) ColorPair {
 	dup := p
 	fgPair := ColorPair{fg.Color, colUndefined, colUndefined, fg.Attr}
@@ -520,6 +526,8 @@ type ColorTheme struct {
 	ListLabel        ColorAttr
 	ListBorder       ColorAttr
 	GapLine          ColorAttr
+	NthCurrentAttr   Attr // raw current-fg attr (before fg merge) for nth overlay
+	NthSelectedAttr  Attr // raw selected-fg attr (before ListFg inherit) for nth overlay
 }
 
 type Event struct {
@@ -1199,13 +1207,19 @@ func InitTheme(theme *ColorTheme, baseTheme *ColorTheme, boldify bool, forceBlac
 		match.Attr = Underline
 	}
 	theme.Match = o(baseTheme.Match, match)
-	// Inherit from 'fg', so that we don't have to write 'current-fg:dim'
+	// These colors are not defined in the base themes.
+	// Resolve ListFg/ListBg early so Current and Selected can inherit from them.
+	theme.ListFg = o(theme.Fg, theme.ListFg)
+	theme.ListBg = o(theme.Bg, theme.ListBg)
+	// Inherit from 'list-fg', so that we don't have to write 'current-fg:dim'
 	// e.g. fzf --delimiter / --nth -1 --color fg:dim,nth:regular
 	current := theme.Current
 	if !baseTheme.Colored && current.IsUndefined() {
 		current.Attr |= Reverse
 	}
-	theme.Current = theme.Fg.Merge(o(baseTheme.Current, current))
+	resolvedCurrent := o(baseTheme.Current, current)
+	theme.NthCurrentAttr = resolvedCurrent.Attr
+	theme.Current = theme.ListFg.Merge(resolvedCurrent)
 	currentMatch := theme.CurrentMatch
 	if !baseTheme.Colored && currentMatch.IsUndefined() {
 		currentMatch.Attr |= Reverse | Underline
@@ -1230,10 +1244,8 @@ func InitTheme(theme *ColorTheme, baseTheme *ColorTheme, boldify bool, forceBlac
 	scrollbarDefined := theme.Scrollbar != undefined
 	previewBorderDefined := theme.PreviewBorder != undefined
 
-	// These colors are not defined in the base themes
+	theme.NthSelectedAttr = theme.SelectedFg.Attr
-	theme.ListFg = o(theme.Fg, theme.ListFg)
+	theme.SelectedFg = theme.ListFg.Merge(theme.SelectedFg)
-	theme.ListBg = o(theme.Bg, theme.ListBg)
-	theme.SelectedFg = o(theme.ListFg, theme.SelectedFg)
 	theme.SelectedBg = o(theme.ListBg, theme.SelectedBg)
 	theme.SelectedMatch = o(theme.Match, theme.SelectedMatch)
 

test/test_core.rb

@@ -1745,6 +1745,191 @@ class TestCore < TestInteractive
     end
   end
 
+  def test_change_with_nth
+    input = [
+      'foo bar baz',
+      'aaa bbb ccc',
+      'xxx yyy zzz'
+    ]
+    writelines(input)
+    # Start with field 1 only, cycle through fields, verify $FZF_WITH_NTH via prompt
+    tmux.send_keys %(#{FZF} --with-nth 1 --bind 'space:change-with-nth(2|3|1),result:transform-prompt:echo "[$FZF_WITH_NTH]> "' < #{tempname}), :Enter
+    tmux.until do |lines|
+      assert_equal 3, lines.item_count
+      assert lines.any_include?('[1]>')
+      assert lines.any_include?('foo')
+      refute lines.any_include?('bar')
+    end
+    tmux.send_keys :Space
+    tmux.until do |lines|
+      assert lines.any_include?('[2]>')
+      assert lines.any_include?('bar')
+      refute lines.any_include?('foo')
+    end
+    tmux.send_keys :Space
+    tmux.until do |lines|
+      assert lines.any_include?('[3]>')
+      assert lines.any_include?('baz')
+      refute lines.any_include?('bar')
+    end
+    tmux.send_keys :Space
+    tmux.until do |lines|
+      assert lines.any_include?('[1]>')
+      assert lines.any_include?('foo')
+      refute lines.any_include?('bar')
+    end
+  end
+
+  def test_change_with_nth_default
+    # Empty value restores the default --with-nth
+    tmux.send_keys %(echo -e 'a b c\nd e f' | #{FZF} --with-nth 1 --bind 'space:change-with-nth(2|)'), :Enter
+    tmux.until do |lines|
+      assert_equal 2, lines.item_count
+      assert lines.any_include?('a')
+      refute lines.any_include?('b')
+    end
+    # Switch to field 2
+    tmux.send_keys :Space
+    tmux.until do |lines|
+      assert lines.any_include?('b')
+      refute lines.any_include?('a')
+    end
+    # Empty restores default (field 1)
+    tmux.send_keys :Space
+    tmux.until do |lines|
+      assert lines.any_include?('a')
+      refute lines.any_include?('b')
+    end
+  end
+
+  def test_transform_with_nth_search
+    input = [
+      'alpha bravo charlie',
+      'delta echo foxtrot',
+      'golf hotel india'
+    ]
+    writelines(input)
+    tmux.send_keys %(#{FZF} --with-nth 1 --bind 'space:transform-with-nth(echo 2)' -q '^bravo$' < #{tempname}), :Enter
+    tmux.until do |lines|
+      assert_equal 0, lines.match_count
+    end
+    tmux.send_keys :Space
+    tmux.until do |lines|
+      assert_equal 1, lines.match_count
+    end
+  end
+
+  def test_bg_transform_with_nth_output
+    tmux.send_keys %(echo -e 'a b c\nd e f' | #{FZF} --with-nth 2 --bind 'space:bg-transform-with-nth(echo 3)'), :Enter
+    tmux.until do |lines|
+      assert_equal 2, lines.item_count
+      assert lines.any_include?('b')
+    end
+    tmux.send_keys :Space
+    tmux.until do |lines|
+      assert lines.any_include?('c')
+      refute lines.any_include?('b')
+    end
+    tmux.send_keys :Enter
+    tmux.until { |lines| assert lines.any_include?('a b c') || lines.any_include?('d e f') }
+  end
+
+  def test_change_with_nth_search
+    input = [
+      'alpha bravo charlie',
+      'delta echo foxtrot',
+      'golf hotel india'
+    ]
+    writelines(input)
+    tmux.send_keys %(#{FZF} --with-nth 1 --bind 'space:change-with-nth(2)' -q '^bravo$' < #{tempname}), :Enter
+    tmux.until do |lines|
+      assert_equal 0, lines.match_count
+    end
+    tmux.send_keys :Space
+    tmux.until do |lines|
+      assert_equal 1, lines.match_count
+    end
+  end
+
+  def test_change_with_nth_output
+    tmux.send_keys %(echo -e 'a b c\nd e f' | #{FZF} --with-nth 2 --bind 'space:change-with-nth(3)'), :Enter
+    tmux.until do |lines|
+      assert_equal 2, lines.item_count
+      assert lines.any_include?('b')
+    end
+    tmux.send_keys :Space
+    tmux.until do |lines|
+      assert lines.any_include?('c')
+      refute lines.any_include?('b')
+    end
+    tmux.send_keys :Enter
+    tmux.until { |lines| assert lines.any_include?('a b c') || lines.any_include?('d e f') }
+  end
+
+  def test_change_with_nth_selection
+    # Items: field1 has unique values, field2 has 'match' or 'miss'
+    input = [
+      'one match x',
+      'two miss y',
+      'three match z'
+    ]
+    writelines(input)
+    # Start showing field 2 (match/miss), query 'match', select all matches, then switch to field 3
+    tmux.send_keys %(#{FZF} --with-nth 2 --multi --bind 'ctrl-a:select-all,space:change-with-nth(3)' -q match < #{tempname}), :Enter
+    tmux.until do |lines|
+      assert_equal 2, lines.match_count
+    end
+    # Select all matching items
+    tmux.send_keys 'C-a'
+    tmux.until do |lines|
+      assert lines.any_include?('(2)')
+    end
+    # Now change with-nth to field 3; 'x' and 'z' don't contain 'match'
+    tmux.send_keys :Space
+    tmux.until do |lines|
+      assert_equal 0, lines.match_count
+      # Selections of non-matching items should be cleared
+      assert lines.any_include?('(0)')
+    end
+  end
+
+  def test_change_with_nth_multiline
+    # Each item has 3 lines: "N-a\nN-b\nN-c"
+    # --with-nth 1 shows 1 line per item, --with-nth 1..3 shows 3 lines per item
+    tmux.send_keys %(seq 20 | xargs -I{} printf '{}-a\\n{}-b\\n{}-c\\0' | #{FZF} --read0 --delimiter "\n" --with-nth 1 --bind 'space:change-with-nth(1..3|1)' --no-sort), :Enter
+    tmux.until do |lines|
+      assert_equal 20, lines.item_count
+      assert lines.any_include?('1-a')
+      refute lines.any_include?('1-b')
+    end
+    # Expand to 3 lines per item
+    tmux.send_keys :Space
+    tmux.until do |lines|
+      assert lines.any_include?('1-a')
+      assert lines.any_include?('1-b')
+      assert lines.any_include?('1-c')
+    end
+    # Scroll down a few items
+    5.times { tmux.send_keys :Down }
+    tmux.until do |lines|
+      assert lines.any_include?('6-a')
+      assert lines.any_include?('6-b')
+      assert lines.any_include?('6-c')
+    end
+    # Collapse back to 1 line per item
+    tmux.send_keys :Space
+    tmux.until do |lines|
+      assert lines.any_include?('6-a')
+      refute lines.any_include?('6-b')
+    end
+    # Scroll down more after collapse
+    5.times { tmux.send_keys :Down }
+    tmux.until do |lines|
+      assert lines.any_include?('11-a')
+      refute lines.any_include?('11-b')
+    end
+  end
+
   def test_env_vars
     def env_vars
       return {} unless File.exist?(tempname)
@@ -1755,7 +1940,7 @@ class TestCore < TestInteractive
       end
     end
 
-    tmux.send_keys %(seq 100 | #{FZF} --multi --reverse --preview-window 0 --preview 'env | grep ^FZF_ | sort > #{tempname}' --no-input --bind enter:show-input+refresh-preview,space:disable-search+refresh-preview), :Enter
+    tmux.send_keys %({ echo foo; seq 100; } | #{FZF} --header-lines 1 --multi --reverse --preview-window 0 --preview 'env | grep ^FZF_ | sort > #{tempname}' --no-input --bind enter:show-input+refresh-preview,space:disable-search+refresh-preview), :Enter
     expected = {
       FZF_DIRECTION: 'down',
       FZF_TOTAL_COUNT: '100',
@@ -2176,6 +2361,80 @@ class TestCore < TestInteractive
     end
   end
 
+  def test_change_header_lines
+    tmux.send_keys %(seq 10 | #{FZF} --header-lines 3 --bind 'space:change-header-lines(5),enter:transform-header-lines(echo 1)'), :Enter
+    tmux.until do |lines|
+      assert_equal 7, lines.item_count
+      assert lines.any_include?('> 4')
+    end
+    tmux.send_keys :Space
+    tmux.until do |lines|
+      assert_equal 5, lines.item_count
+      assert lines.any_include?('> 6')
+    end
+    tmux.send_keys :Enter
+    tmux.until do |lines|
+      assert_equal 9, lines.item_count
+      assert lines.any_include?('> 6')
+    end
+  end
+
+  def test_change_header_lines_to_zero
+    tmux.send_keys %(seq 5 | #{FZF} --header-lines 3 --bind 'space:bg-transform-header-lines(echo 0)'), :Enter
+    tmux.until do |lines|
+      assert_equal 2, lines.item_count
+      assert lines.any_include?('> 4')
+    end
+    tmux.send_keys :Space
+    tmux.until do |lines|
+      assert_equal 5, lines.item_count
+      # All items are now in the list, cursor stays on item 4
+      assert lines.any_include?('> 4')
+    end
+  end
+
+  def test_change_header_lines_deselect
+    # Selected items that become part of the header should be deselected
+    tmux.send_keys %(seq 10 | #{FZF} --multi --header-lines 0 --bind 'space:change-header-lines(3),enter:change-header-lines(1)'), :Enter
+    tmux.until do |lines|
+      assert_equal 10, lines.item_count
+      assert lines.any_include?('> 1')
+    end
+    # Select items 1, 2, 3 (these will become header lines)
+    tmux.send_keys :BTab, :BTab, :BTab
+    tmux.until { |lines| assert_equal 3, lines.select_count }
+    # Also select item 4 (this should remain selected)
+    tmux.send_keys :BTab
+    tmux.until { |lines| assert_equal 4, lines.select_count }
+    # Change header-lines to 3: items 1, 2, 3 become headers and should be deselected
+    tmux.send_keys :Space
+    tmux.until do |lines|
+      assert_equal 7, lines.item_count
+      assert_equal 1, lines.select_count
+      assert lines.any_include?('> 5')
+    end
+    # Change header-lines to 1
+    tmux.send_keys :Enter
+    tmux.until do |lines|
+      assert_equal 9, lines.item_count
+      assert_equal 1, lines.select_count
+      assert lines.any_include?('> 5')
+    end
+  end
+
+  def test_change_header_lines_reverse
+    tmux.send_keys %(seq 10 | #{FZF} --header-lines 2 --reverse --bind 'space:change-header-lines(4)'), :Enter
+    tmux.until do |lines|
+      assert_equal 8, lines.item_count
+      assert lines.any_include?('> 3')
+    end
+    tmux.send_keys :Space
+    tmux.until do |lines|
+      assert_equal 6, lines.item_count
+      assert lines.any_include?('> 5')
+    end
+  end
+
   def test_zero_width_characters
     tmux.send_keys %(for i in {1..1000}; do string+="a̱$i"; printf '\\e[43m%s\\e[0m\\n' "$string"; done | #{FZF} --ansi --query a500 --ellipsis XX), :Enter
     tmux.until do |lines|

test/test_filter.rb

@@ -326,4 +326,27 @@ class TestFilter < TestBase
     writelines(['emp001 Alice Engineering', 'emp002 Bob Marketing'])
     assert_equal 'emp001', `#{FZF} -d' ' --with-nth 2 --accept-nth 1 -f Alice < #{tempname}`.chomp
   end
+
+  def test_header_lines_filter
+    assert_equal %w[4 5 6 7 8 9 10],
+                 `seq 10 | #{FZF} --header-lines 3 -f ""`.lines(chomp: true)
+    assert_equal %w[5],
+                 `seq 10 | #{FZF} --header-lines 3 -f 5`.lines(chomp: true)
+    # Header items should not be matched
+    assert_empty `seq 10 | #{FZF} --header-lines 3 -f "^1$"`.lines(chomp: true)
+  end
+
+  def test_header_lines_filter_with_nth
+    writelines(%w[a:1 b:2 c:3 d:4 e:5])
+    assert_equal %w[c:3 d:4 e:5],
+                 `#{FZF} --header-lines 2 -d: --with-nth 2 -f "" < #{tempname}`.lines(chomp: true)
+    assert_equal %w[d:4],
+                 `#{FZF} --header-lines 2 -d: --with-nth 2 -f 4 < #{tempname}`.lines(chomp: true)
+  end
+
+  def test_header_lines_all_headers
+    # When all lines are header lines, no results
+    assert_empty `seq 3 | #{FZF} --header-lines 10 -f ""`.chomp
+    assert_equal 1, $CHILD_STATUS.exitstatus
+  end
 end