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strings: optimize ToLower

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Handling the ASCII case inline and call unicode.ToLower only
for non-ASCII cases.

Gives good improvements for the ASCII case and minor perf
degrade for non-ASCII case

name                                     old time/op    new time/op    delta
ToLower/#00                                10.8ns ± 1%     9.0ns ± 1%  -16.83%  (p=0.008 n=5+5)
ToLower/abc                                23.3ns ± 4%    12.6ns ± 1%  -46.01%  (p=0.008 n=5+5)
ToLower/AbC123                             91.0ns ± 2%    70.4ns ± 0%  -22.59%  (p=0.008 n=5+5)
ToLower/azAZ09_                             104ns ± 3%      75ns ± 1%  -28.35%  (p=0.008 n=5+5)
ToLower/longStrinGwitHmixofsmaLLandcAps     254ns ± 4%     157ns ± 0%  -38.19%  (p=0.016 n=5+4)
ToLower/LONGⱯSTRINGⱯWITHⱯNONASCIIⱯCHARS     446ns ± 1%     451ns ± 1%     ~     (p=0.056 n=5+5)
ToLower/ⱭⱭⱭⱭⱭ                               345ns ± 1%     348ns ± 0%   +0.93%  (p=0.016 n=5+5)

name                                     old alloc/op   new alloc/op   delta
ToLower/#00                                 0.00B          0.00B          ~     (all equal)
ToLower/abc                                 0.00B          0.00B          ~     (all equal)
ToLower/AbC123                              16.0B ± 0%     16.0B ± 0%     ~     (all equal)
ToLower/azAZ09_                             24.0B ± 0%     16.0B ± 0%  -33.33%  (p=0.008 n=5+5)
ToLower/longStrinGwitHmixofsmaLLandcAps     80.0B ± 0%     64.0B ± 0%  -20.00%  (p=0.008 n=5+5)
ToLower/LONGⱯSTRINGⱯWITHⱯNONASCIIⱯCHARS     96.0B ± 0%     96.0B ± 0%     ~     (all equal)
ToLower/ⱭⱭⱭⱭⱭ                               48.0B ± 0%     48.0B ± 0%     ~     (all equal)

Ran on a machine with Intel(R) Core(TM) i5-5200U CPU @ 2.20GHz

Fixes #17859

Change-Id: Iacc1e6b77e1aedba9447a6e94352606f131ea597
Reviewed-on: https://go-review.googlesource.com/76470
Reviewed-by: Marvin Stenger <marvin.stenger94@gmail.com>
Reviewed-by: Joe Tsai <thebrokentoaster@gmail.com>
This commit is contained in:
Agniva De Sarker 2017-11-08 09:15:53 +05:30 • committed by Joe Tsai
parent 506386fd37
commit 65fbf0e834
2 changed files with 42 additions and 1 deletions
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15
src/strings/strings_test.go
View file

@ -532,6 +532,8 @@ var lowerTests = []StringTest{
{"abc", "abc"},
{"AbC123", "abc123"},
{"azAZ09_", "azaz09_"},
{"longStrinGwitHmixofsmaLLandcAps", "longstringwithmixofsmallandcaps"},
{"LONG\u2C6FSTRING\u2C6FWITH\u2C6FNONASCII\u2C6FCHARS", "long\u0250string\u0250with\u0250nonascii\u0250chars"},
{"\u2C6D\u2C6D\u2C6D\u2C6D\u2C6D", "\u0251\u0251\u0251\u0251\u0251"}, // shrinks one byte per char
}
@ -664,6 +666,19 @@ func BenchmarkToUpper(b *testing.B) {
}
}
func BenchmarkToLower(b *testing.B) {
for _, tc := range lowerTests {
b.Run(tc.in, func(b *testing.B) {
for i := 0; i < b.N; i++ {
actual := ToLower(tc.in)
if actual != tc.out {
b.Errorf("ToLower(%q) = %q; want %q", tc.in, actual, tc.out)
}
}
})
}
}
func BenchmarkMapNoChanges(b *testing.B) {
identity := func(r rune) rune {
return r