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bytes, strings: optimize Trim for single byte cutsets

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Using the latest version of all modules known by the module proxy,
we determine that for all Trim usages (and related functionality):
* 76.6% have cutsets of len=1, and
* 13.4% have cutsets of len=2.

Given that a vast majority of usages only have a cutset of len=1,
we should more heavily optimize for that situation.
Previously, there was some optimization for cutsets of len=1,
but it's within the internal makeCutsetFunc function.
This is sub-optimal as it incurs an allocation in makeCutsetFunc
for the closure over that single byte.

This CL removes special-casing of one-byte cutsets from makeCutsetFunc
and instead distributes it directly in Trim, TrimRight, and TrimLeft.
Whether we should distribute the entire ASCII cutset logic into Trim
is a future CL that should be discussed and handled separately.
The evidence for multibyte cutsets is not as obviously compelling.

name                old time/op  new time/op  delta
bytes/TrimByte-4    84.1ns ± 2%   7.5ns ± 1%  -91.10%  (p=0.000 n=9+7)
strings/TrimByte-4  86.2ns ± 3%   8.3ns ± 1%  -90.33%  (p=0.000 n=9+10)

Fixes #46446

Change-Id: Ia0e31a8384c3ce111ae35465605bcec45df2ebec
Reviewed-on: https://go-review.googlesource.com/c/go/+/323318
Trust: Joe Tsai <joetsai@digital-static.net>
Run-TryBot: Joe Tsai <joetsai@digital-static.net>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
This commit is contained in:
Joe Tsai 2021-05-29 19:11:37 -07:00
parent 3d667671ad
commit 5baf60d472
4 changed files with 64 additions and 10 deletions
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9
src/bytes/bytes_test.go
View file

@ -1251,7 +1251,9 @@ var trimTests = []TrimTest{
{"TrimLeft", "abba", "ab", ""},
{"TrimRight", "abba", "ab", ""},
{"TrimLeft", "abba", "a", "bba"},
{"TrimLeft", "abba", "b", "abba"},
{"TrimRight", "abba", "a", "abb"},
{"TrimRight", "abba", "b", "abba"},
{"Trim", "<tag>", "<>", "tag"},
{"Trim", "* listitem", " *", "listitem"},
{"Trim", `"quote"`, `"`, "quote"},
@ -1963,6 +1965,13 @@ func BenchmarkTrimASCII(b *testing.B) {
}
}
func BenchmarkTrimByte(b *testing.B) {
x := []byte(" the quick brown fox ")
for i := 0; i < b.N; i++ {
Trim(x, " ")
}
}
func BenchmarkIndexPeriodic(b *testing.B) {
key := []byte{1, 1}
for _, skip := range [...]int{2, 4, 8, 16, 32, 64} {