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strings: speed up Map
name old time/op new time/op delta ByteByteMap-4 2.03µs ± 2% 1.03µs ± 2% -49.24% (p=0.000 n=10+10) Map/identity/ASCII-4 246ns ± 0% 158ns ± 0% -35.90% (p=0.000 n=9+9) Map/identity/Greek-4 367ns ± 1% 273ns ± 1% -25.63% (p=0.000 n=10+10) Map/change/ASCII-4 582ns ± 1% 324ns ± 1% -44.34% (p=0.000 n=10+10) Map/change/Greek-4 709ns ± 2% 623ns ± 2% -12.16% (p=0.000 n=10+10) MapNoChanges-4 171ns ± 1% 111ns ± 1% -35.36% (p=0.000 n=8+10) Updates #17859 Change-Id: I55d7d261fdc1ce2dcd0ebe23b0fa20b9889bf54c Reviewed-on: https://go-review.googlesource.com/33201 Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org> Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org> TryBot-Result: Gobot Gobot <gobot@golang.org>
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@ -540,3 +540,44 @@ func BenchmarkByteByteMap(b *testing.B) {
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Map(fn, str)
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}
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}
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var mapdata = []struct{ name, data string }{
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{"ASCII", "a b c d e f g h i j k l m n o p q r s t u v w x y z"},
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{"Greek", "α β γ δ ε ζ η θ ι κ λ μ ν ξ ο π ρ ς σ τ υ φ χ ψ ω"},
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}
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func BenchmarkMap(b *testing.B) {
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mapidentity := func(r rune) rune {
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return r
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}
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b.Run("identity", func(b *testing.B) {
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for _, md := range mapdata {
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b.Run(md.name, func(b *testing.B) {
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for i := 0; i < b.N; i++ {
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Map(mapidentity, md.data)
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}
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})
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}
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})
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mapchange := func(r rune) rune {
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if 'a' <= r && r <= 'z' {
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return r + 'A' - 'a'
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}
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if 'α' <= r && r <= 'ω' {
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return r + 'Α' - 'α'
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}
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return r
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}
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b.Run("change", func(b *testing.B) {
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for _, md := range mapdata {
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b.Run(md.name, func(b *testing.B) {
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for i := 0; i < b.N; i++ {
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Map(mapchange, md.data)
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}
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})
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}
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})
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}
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@ -383,40 +383,61 @@ func Map(mapping func(rune) rune, s string) string {
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// In the worst case, the string can grow when mapped, making
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// things unpleasant. But it's so rare we barge in assuming it's
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// fine. It could also shrink but that falls out naturally.
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maxbytes := len(s) // length of b
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nbytes := 0 // number of bytes encoded in b
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// The output buffer b is initialized on demand, the first
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// time a character differs.
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var b []byte
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// nbytes is the number of bytes encoded in b.
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var nbytes int
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for i, c := range s {
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r := mapping(c)
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if b == nil {
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if r == c {
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continue
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}
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b = make([]byte, maxbytes)
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nbytes = copy(b, s[:i])
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if r == c {
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continue
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}
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b = make([]byte, len(s)+utf8.UTFMax)
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nbytes = copy(b, s[:i])
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if r >= 0 {
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wid := 1
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if r >= utf8.RuneSelf {
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wid = utf8.RuneLen(r)
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if r <= utf8.RuneSelf {
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b[nbytes] = byte(r)
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nbytes++
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} else {
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nbytes += utf8.EncodeRune(b[nbytes:], r)
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}
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if nbytes+wid > maxbytes {
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// Grow the buffer.
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maxbytes = maxbytes*2 + utf8.UTFMax
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nb := make([]byte, maxbytes)
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copy(nb, b[0:nbytes])
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b = nb
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}
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nbytes += utf8.EncodeRune(b[nbytes:maxbytes], r)
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}
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i += utf8.RuneLen(c)
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s = s[i:]
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break
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}
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if b == nil {
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return s
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}
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return string(b[0:nbytes])
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for _, c := range s {
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r := mapping(c)
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// common case
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if (0 <= r && r <= utf8.RuneSelf) && nbytes < len(b) {
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b[nbytes] = byte(r)
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nbytes++
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continue
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}
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// b is not big enough or r is not a ASCII rune.
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if r >= 0 {
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if nbytes+utf8.UTFMax >= len(b) {
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// Grow the buffer.
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nb := make([]byte, 2*len(b))
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copy(nb, b[:nbytes])
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b = nb
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}
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nbytes += utf8.EncodeRune(b[nbytes:], r)
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}
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}
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return string(b[:nbytes])
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}
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// Repeat returns a new string consisting of count copies of the string s.
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