strings: use Builder in ToUpper and ToLower

tmthrgd · bradfitz · commit 14e7f174c1bf · 2018-09-26T14:41:52.000Z
Map was optimized to use Builder in 45c7d80, which avoided the []byte to string converstion. This left the ToUpper and ToLower ASCII fast path with an extra allocation over Map. name old time/op new time/op delta ToUpper/#00-12 3.59ns ± 4% 3.71ns ± 1% ~ (p=0.056 n=5+5) ToUpper/ONLYUPPER-12 11.8ns ± 2% 10.5ns ± 2% -10.85% (p=0.008 n=5+5) ToUpper/abc-12 31.8ns ± 1% 25.3ns ± 1% -20.40% (p=0.008 n=5+5) ToUpper/AbC123-12 46.2ns ± 7% 31.9ns ± 8% -30.89% (p=0.008 n=5+5) ToUpper/azAZ09_-12 47.1ns ± 8% 32.6ns ± 4% -30.77% (p=0.008 n=5+5) ToUpper/longStrinGwitHmixofsmaLLandcAps-12 137ns ±15% 104ns ±11% -24.11% (p=0.008 n=5+5) ToUpper/longɐstringɐwithɐnonasciiⱯchars-12 231ns ± 1% 228ns ± 1% ~ (p=0.079 n=5+5) ToUpper/ɐɐɐɐɐ-12 207ns ± 3% 206ns ± 1% ~ (p=0.913 n=5+5) ToUpper/a\u0080\U0010ffff-12 90.8ns ± 1% 89.6ns ± 1% -1.30% (p=0.024 n=5+5) ToLower/#00-12 3.59ns ± 1% 4.26ns ± 2% +18.66% (p=0.008 n=5+5) ToLower/abc-12 6.32ns ± 1% 6.62ns ± 1% +4.72% (p=0.008 n=5+5) ToLower/AbC123-12 45.0ns ±13% 31.5ns ± 4% -29.89% (p=0.008 n=5+5) ToLower/azAZ09_-12 48.8ns ± 6% 33.2ns ± 3% -31.91% (p=0.008 n=5+5) ToLower/longStrinGwitHmixofsmaLLandcAps-12 149ns ±13% 98ns ± 8% -34.30% (p=0.008 n=5+5) ToLower/LONGⱯSTRINGⱯWITHⱯNONASCIIⱯCHARS-12 237ns ± 4% 237ns ± 2% ~ (p=0.635 n=5+5) ToLower/ⱭⱭⱭⱭⱭ-12 181ns ± 1% 181ns ± 1% ~ (p=0.762 n=5+5) ToLower/A\u0080\U0010ffff-12 90.6ns ± 1% 92.5ns ± 1% +2.05% (p=0.016 n=5+5) name old alloc/op new alloc/op delta ToUpper/#00-12 0.00B 0.00B ~ (all equal) ToUpper/ONLYUPPER-12 0.00B 0.00B ~ (all equal) ToUpper/abc-12 6.00B ± 0% 3.00B ± 0% -50.00% (p=0.008 n=5+5) ToUpper/AbC123-12 16.0B ± 0% 8.0B ± 0% -50.00% (p=0.008 n=5+5) ToUpper/azAZ09_-12 16.0B ± 0% 8.0B ± 0% -50.00% (p=0.008 n=5+5) ToUpper/longStrinGwitHmixofsmaLLandcAps-12 64.0B ± 0% 32.0B ± 0% -50.00% (p=0.008 n=5+5) ToUpper/longɐstringɐwithɐnonasciiⱯchars-12 48.0B ± 0% 48.0B ± 0% ~ (all equal) ToUpper/ɐɐɐɐɐ-12 48.0B ± 0% 48.0B ± 0% ~ (all equal) ToUpper/a\u0080\U0010ffff-12 16.0B ± 0% 16.0B ± 0% ~ (all equal) ToLower/#00-12 0.00B 0.00B ~ (all equal) ToLower/abc-12 0.00B 0.00B ~ (all equal) ToLower/AbC123-12 16.0B ± 0% 8.0B ± 0% -50.00% (p=0.008 n=5+5) ToLower/azAZ09_-12 16.0B ± 0% 8.0B ± 0% -50.00% (p=0.008 n=5+5) ToLower/longStrinGwitHmixofsmaLLandcAps-12 64.0B ± 0% 32.0B ± 0% -50.00% (p=0.008 n=5+5) ToLower/LONGⱯSTRINGⱯWITHⱯNONASCIIⱯCHARS-12 48.0B ± 0% 48.0B ± 0% ~ (all equal) ToLower/ⱭⱭⱭⱭⱭ-12 32.0B ± 0% 32.0B ± 0% ~ (all equal) ToLower/A\u0080\U0010ffff-12 16.0B ± 0% 16.0B ± 0% ~ (all equal) name old allocs/op new allocs/op delta ToUpper/#00-12 0.00 0.00 ~ (all equal) ToUpper/ONLYUPPER-12 0.00 0.00 ~ (all equal) ToUpper/abc-12 2.00 ± 0% 1.00 ± 0% -50.00% (p=0.008 n=5+5) ToUpper/AbC123-12 2.00 ± 0% 1.00 ± 0% -50.00% (p=0.008 n=5+5) ToUpper/azAZ09_-12 2.00 ± 0% 1.00 ± 0% -50.00% (p=0.008 n=5+5) ToUpper/longStrinGwitHmixofsmaLLandcAps-12 2.00 ± 0% 1.00 ± 0% -50.00% (p=0.008 n=5+5) ToUpper/longɐstringɐwithɐnonasciiⱯchars-12 1.00 ± 0% 1.00 ± 0% ~ (all equal) ToUpper/ɐɐɐɐɐ-12 2.00 ± 0% 2.00 ± 0% ~ (all equal) ToUpper/a\u0080\U0010ffff-12 1.00 ± 0% 1.00 ± 0% ~ (all equal) ToLower/#00-12 0.00 0.00 ~ (all equal) ToLower/abc-12 0.00 0.00 ~ (all equal) ToLower/AbC123-12 2.00 ± 0% 1.00 ± 0% -50.00% (p=0.008 n=5+5) ToLower/azAZ09_-12 2.00 ± 0% 1.00 ± 0% -50.00% (p=0.008 n=5+5) ToLower/longStrinGwitHmixofsmaLLandcAps-12 2.00 ± 0% 1.00 ± 0% -50.00% (p=0.008 n=5+5) ToLower/LONGⱯSTRINGⱯWITHⱯNONASCIIⱯCHARS-12 1.00 ± 0% 1.00 ± 0% ~ (all equal) ToLower/ⱭⱭⱭⱭⱭ-12 1.00 ± 0% 1.00 ± 0% ~ (all equal) ToLower/A\u0080\U0010ffff-12 1.00 ± 0% 1.00 ± 0% ~ (all equal) Updates #26304 Change-Id: I4179e21d5e60d950b925fe3ffc74b376b82812d2 GitHub-Last-Rev: 2c7c3bb GitHub-Pull-Request: #27872 Reviewed-on: https://go-review.googlesource.com/137575 Run-TryBot: Ian Lance Taylor <iant@golang.org> TryBot-Result: Gobot Gobot <gobot@golang.org> Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
diff --git a/src/strings/strings.go b/src/strings/strings.go
@@ -561,15 +561,16 @@ func ToUpper(s string) string {
 		if !hasLower {
 			return s
 		}
-		b := make([]byte, len(s))
+		var b Builder
+		b.Grow(len(s))
 		for i := 0; i < len(s); i++ {
 			c := s[i]
 			if c >= 'a' && c <= 'z' {
 				c -= 'a' - 'A'
 			}
-			b[i] = c
+			b.WriteByte(c)
 		}
-		return string(b)
+		return b.String()
 	}
 	return Map(unicode.ToUpper, s)
 }
@@ -590,15 +591,16 @@ func ToLower(s string) string {
 		if !hasUpper {
 			return s
 		}
-		b := make([]byte, len(s))
+		var b Builder
+		b.Grow(len(s))
 		for i := 0; i < len(s); i++ {
 			c := s[i]
 			if c >= 'A' && c <= 'Z' {
 				c += 'a' - 'A'
 			}
-			b[i] = c
+			b.WriteByte(c)
 		}
-		return string(b)
+		return b.String()
 	}
 	return Map(unicode.ToLower, s)
 }

Original file line number	Diff line number	Diff line change
`@@ -561,15 +561,16 @@ func ToUpper(s string) string {`
`561`	`561`	`if !hasLower {`
`562`	`562`	`return s`
`563`	`563`	`}`
`564`		`- b := make([]byte, len(s))`
	`564`	`+ var b Builder`
	`565`	`+ b.Grow(len(s))`
`565`	`566`	`for i := 0; i < len(s); i++ {`
`566`	`567`	`c := s[i]`
`567`	`568`	`if c >= 'a' && c <= 'z' {`
`568`	`569`	`c -= 'a' - 'A'`
`569`	`570`	`}`
`570`		`- b[i] = c`
	`571`	`+ b.WriteByte(c)`
`571`	`572`	`}`
`572`		`- return string(b)`
	`573`	`+ return b.String()`
`573`	`574`	`}`
`574`	`575`	`return Map(unicode.ToUpper, s)`
`575`	`576`	`}`
`@@ -590,15 +591,16 @@ func ToLower(s string) string {`
`590`	`591`	`if !hasUpper {`
`591`	`592`	`return s`
`592`	`593`	`}`
`593`		`- b := make([]byte, len(s))`
	`594`	`+ var b Builder`
	`595`	`+ b.Grow(len(s))`
`594`	`596`	`for i := 0; i < len(s); i++ {`
`595`	`597`	`c := s[i]`
`596`	`598`	`if c >= 'A' && c <= 'Z' {`
`597`	`599`	`c += 'a' - 'A'`
`598`	`600`	`}`
`599`		`- b[i] = c`
	`601`	`+ b.WriteByte(c)`
`600`	`602`	`}`
`601`		`- return string(b)`
	`603`	`+ return b.String()`
`602`	`604`	`}`
`603`	`605`	`return Map(unicode.ToLower, s)`
`604`	`606`	`}`