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strings: use Builder in Repeat to avoid an allocation
name old time/op new time/op delta
Repeat/5x1-4 95.9ns ± 2% 70.1ns ± 2% -26.93% (p=0.000 n=9+10)
Repeat/5x2-4 146ns ± 3% 100ns ± 2% -31.99% (p=0.000 n=10+10)
Repeat/5x6-4 203ns ± 3% 140ns ± 4% -30.77% (p=0.000 n=10+10)
Repeat/10x1-4 139ns ± 3% 92ns ± 4% -34.08% (p=0.000 n=10+10)
Repeat/10x2-4 188ns ± 4% 122ns ± 2% -35.34% (p=0.000 n=10+10)
Repeat/10x6-4 264ns ± 5% 179ns ± 4% -32.15% (p=0.000 n=10+10)
name old alloc/op new alloc/op delta
Repeat/5x1-4 10.0B ± 0% 5.0B ± 0% -50.00% (p=0.000 n=10+10)
Repeat/5x2-4 32.0B ± 0% 16.0B ± 0% -50.00% (p=0.000 n=10+10)
Repeat/5x6-4 64.0B ± 0% 32.0B ± 0% -50.00% (p=0.000 n=10+10)
Repeat/10x1-4 32.0B ± 0% 16.0B ± 0% -50.00% (p=0.000 n=10+10)
Repeat/10x2-4 64.0B ± 0% 32.0B ± 0% -50.00% (p=0.000 n=10+10)
Repeat/10x6-4 128B ± 0% 64B ± 0% -50.00% (p=0.000 n=10+10)
Change-Id: I6619336da636df39c560f6cc481519f48c6e8176
GitHub-Last-Rev: 4b2c73f3bf
GitHub-Pull-Request: golang/go#25894
Reviewed-on: https://go-review.googlesource.com/118855
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
This commit is contained in:
parent
6a11e1e8db
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@ -523,23 +523,33 @@ func Map(mapping func(rune) rune, s string) string {
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// It panics if count is negative or if
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// the result of (len(s) * count) overflows.
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func Repeat(s string, count int) string {
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if count == 0 {
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return ""
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}
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// Since we cannot return an error on overflow,
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// we should panic if the repeat will generate
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// an overflow.
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// See Issue golang.org/issue/16237
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if count < 0 {
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panic("strings: negative Repeat count")
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} else if count > 0 && len(s)*count/count != len(s) {
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} else if len(s)*count/count != len(s) {
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panic("strings: Repeat count causes overflow")
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}
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b := make([]byte, len(s)*count)
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bp := copy(b, s)
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for bp < len(b) {
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copy(b[bp:], b[:bp])
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bp *= 2
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n := len(s) * count
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var b Builder
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b.Grow(n)
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b.WriteString(s)
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for b.Len() < n {
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if b.Len() <= n/2 {
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b.WriteString(b.String())
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} else {
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b.WriteString(b.String()[:n-b.Len()])
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break
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}
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}
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return string(b)
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return b.String()
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}
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// ToUpper returns a copy of the string s with all Unicode letters mapped to their upper case.
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@ -1660,8 +1660,15 @@ func BenchmarkSplitNMultiByteSeparator(b *testing.B) {
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}
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func BenchmarkRepeat(b *testing.B) {
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for i := 0; i < b.N; i++ {
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Repeat("-", 80)
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s := "0123456789"
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for _, n := range []int{5, 10} {
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for _, c := range []int{1, 2, 6} {
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b.Run(fmt.Sprintf("%dx%d", n, c), func(b *testing.B) {
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for i := 0; i < b.N; i++ {
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Repeat(s[:n], c)
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}
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})
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}
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}
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}
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