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perf(emoji): optimize FindEmojiSubmatchIndex using slice-based Trie (#38573)

Browse Source 
This pull request optimizes `FindEmojiSubmatchIndex` in Gitea's emoji
package (`modules/emoji/emoji.go`) by replacing the
`strings.Replacer`-based search with a slice-based trie and a
constant-time starting-byte check (`isStartingByte`).

The new implementation avoids heap allocations during the search and
reduces CPU overhead when rendering Markdown, particularly for plain
text that does not contain emojis.

### Verification

Verified with unit tests:

```sh
go test -count=1 ./modules/emoji/...
```

Benchmarks:

```sh
go test -bench=. -benchmem ./modules/emoji/...
```

### Results

| Benchmark | Before | After |
| ---------- | ------ | ----- |
| `BenchmarkFindEmojiSubmatchIndex` | 168.3 ns/op, 2 allocs/op | 85.78
ns/op, 1 alloc/op |
| `BenchmarkFindEmojiSubmatchIndexNoMatch` | 239.8 ns/op, 1 alloc/op |
105.1 ns/op, 0 allocs/op |
### Benchmark Output

```text
goos: linux
goarch: amd64
pkg: gitea.dev/modules/emoji
cpu: Intel(R) Core(TM) i5-7400 CPU @ 3.00GHz

BenchmarkFindEmojiSubmatchIndex-4              13498539        85.78 ns/op      16 B/op   1 allocs/op
BenchmarkFindEmojiSubmatchIndexNoMatch-4       11220450       105.1 ns/op        0 B/op   0 allocs/op
BenchmarkFindEmojiSubmatchIndexOld-4            6569360       168.3 ns/op      48 B/op   2 allocs/op
BenchmarkFindEmojiSubmatchIndexOldNoMatch-4     5026116       239.8 ns/op      32 B/op   1 allocs/op
```

---------

Signed-off-by: Sudhanshu Singh <sudhanshuwriterblc@gmail.com>
Co-authored-by: silverwind <me@silverwind.io>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
This commit is contained in:
Shudhanshu Singh
2026-07-23 08:29:28 +00:00
committed by GitHub
co-authored by silverwind wxiaoguang
parent acbdc44d00
commit ee10ae168c
4 changed files with 156 additions and 76 deletions
Download Patch File Download Diff File Expand all files Collapse all files
modules/emoji/emoji.go
+27 -69
View File
@@ -5,12 +5,12 @@
package emoji
import (
"io"
"sort"
"strings"
"sync/atomic"
"gitea.dev/modules/setting"
"gitea.dev/modules/util"
)
// Gemoji is a set of emoji data.
@@ -26,11 +26,12 @@ type Emoji struct {
}
type globalVarsStruct struct {
codeMap map[string]int // emoji unicode code to its emoji data.
aliasMap map[string]int // the alias to its emoji data.
emptyReplacer *strings.Replacer // string replacer for emoji codes, used for finding emoji positions.
codeReplacer *strings.Replacer // string replacer for emoji codes.
aliasReplacer *strings.Replacer // string replacer for emoji aliases.
codeMap map[string]int // emoji Unicode code to its emoji data.
aliasMap map[string]int // the alias to its emoji data.
trie *util.TrieNode // trie for finding emoji positions.
isStartingByte [256]bool // fast-path skip for starting bytes.
codeReplacer *strings.Replacer // string replacer for emoji codes.
aliasReplacer *strings.Replacer // string replacer for emoji aliases.
}
var globalVarsStore atomic.Pointer[globalVarsStruct]
@@ -44,10 +45,10 @@ func globalVars() *globalVarsStruct {
vars = &globalVarsStruct{}
vars.codeMap = make(map[string]int, len(GemojiData))
vars.aliasMap = make(map[string]int, len(GemojiData))
vars.trie = &util.TrieNode{}
// process emoji codes and aliases
codePairs := make([]string, 0)
emptyPairs := make([]string, 0)
aliasPairs := make([]string, 0)
// sort from largest to small so we match combined emoji first
@@ -81,20 +82,20 @@ func globalVars() *globalVarsStruct {
if firstAlias != "" {
vars.codeMap[emoji.Emoji] = idx
codePairs = append(codePairs, emoji.Emoji, ":"+emoji.Aliases[0]+":")
emptyPairs = append(emptyPairs, emoji.Emoji, emoji.Emoji)
vars.trie.Insert(emoji.Emoji)
vars.isStartingByte[emoji.Emoji[0]] = true
}
}
// create replacers
vars.emptyReplacer = strings.NewReplacer(emptyPairs...)
vars.codeReplacer = strings.NewReplacer(codePairs...)
vars.aliasReplacer = strings.NewReplacer(aliasPairs...)
globalVarsStore.Store(vars)
return vars
}
// FromCode retrieves the emoji data based on the provided unicode code (ie,
// "\u2618" will return the Gemoji data for "shamrock").
// FromCode retrieves the emoji data based on the provided Unicode code
// e.g.: "\u2618" will return the Gemoji data for "shamrock".
func FromCode(code string) *Emoji {
i, ok := globalVars().codeMap[code]
if !ok {
@@ -104,9 +105,8 @@ func FromCode(code string) *Emoji {
return &GemojiData[i]
}
// FromAlias retrieves the emoji data based on the provided alias in the form
// "alias" or ":alias:" (ie, "shamrock" or ":shamrock:" will return the Gemoji
// data for "shamrock").
// FromAlias retrieves the emoji data based on the provided alias in the form "alias" or ":alias:"
// e.g.: "shamrock" or ":shamrock:" will return the Gemoji data for "shamrock".
func FromAlias(alias string) *Emoji {
if strings.HasPrefix(alias, ":") && strings.HasSuffix(alias, ":") {
alias = alias[1 : len(alias)-1]
@@ -120,69 +120,27 @@ func FromAlias(alias string) *Emoji {
return &GemojiData[i]
}
// ReplaceCodes replaces all emoji codes with the first corresponding emoji
// alias (in the form of ":alias:") (ie, "\u2618" will be converted to
// ":shamrock:").
// ReplaceCodes replaces all emoji codes with the first corresponding emoji alias in the form of ":alias:"
// e.g.: "\u2618" will be converted to ":shamrock:".
func ReplaceCodes(s string) string {
return globalVars().codeReplacer.Replace(s)
}
// ReplaceAliases replaces all aliases of the form ":alias:" with its
// corresponding unicode value.
// ReplaceAliases replaces all aliases of the form ":alias:" with its corresponding Unicode value.
func ReplaceAliases(s string) string {
return globalVars().aliasReplacer.Replace(s)
}
type rememberSecondWriteWriter struct {
pos int
idx int
end int
writecount int
}
func (n *rememberSecondWriteWriter) Write(p []byte) (int, error) {
n.writecount++
if n.writecount == 2 {
n.idx = n.pos
n.end = n.pos + len(p)
n.pos += len(p)
return len(p), io.EOF
}
n.pos += len(p)
return len(p), nil
}
func (n *rememberSecondWriteWriter) WriteString(s string) (int, error) {
n.writecount++
if n.writecount == 2 {
n.idx = n.pos
n.end = n.pos + len(s)
n.pos += len(s)
return len(s), io.EOF
}
n.pos += len(s)
return len(s), nil
}
// FindEmojiSubmatchIndex returns index pair of longest emoji in a string
// FindEmojiSubmatchIndex returns index-pair of the first emoji in a string
func FindEmojiSubmatchIndex(s string) []int {
secondWriteWriter := rememberSecondWriteWriter{}
// A faster and clean implementation would copy the trie tree formation in strings.NewReplacer but
// we can be lazy here.
//
// The implementation of strings.Replacer.WriteString is such that the first index of the emoji
// submatch is simply the second thing that is written to WriteString in the writer.
//
// Therefore we can simply take the index of the second write as our first emoji
//
// FIXME: just copy the trie implementation from strings.NewReplacer
_, _ = globalVars().emptyReplacer.WriteString(&secondWriteWriter, s)
// if we wrote less than twice then we never "replaced"
if secondWriteWriter.writecount < 2 {
return nil
vars := globalVars()
for i := 0; i < len(s); i++ {
if !vars.isStartingByte[s[i]] {
continue
}
if matchLen := vars.trie.Match(s, i); matchLen > 0 {
return []int{i, i + matchLen}
}
}
return []int{secondWriteWriter.idx, secondWriteWriter.end}
return nil
}