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time/format: avoid growslice in time.String()/time.GoString()

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Pre-allocate the slice of buf with enough capacity
to avoid growslice calls.

benchmark                   old ns/op     new ns/op     delta
BenchmarkTimeString-4       493           409           -17.12%
BenchmarkTimeGoString-4     309           182           -41.30%

benchmark                   old allocs     new allocs     delta
BenchmarkTimeString-4       5              3              -40.00%
BenchmarkTimeGoString-4     4              1              -75.00%

benchmark                   old bytes     new bytes     delta
BenchmarkTimeString-4       152           128           -15.79%
BenchmarkTimeGoString-4     248           80            -67.74%

Change-Id: I64eabe2ab0b3d4a846453c2e8e548a831d720b8c
Reviewed-on: https://go-review.googlesource.com/c/go/+/343971
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Trust: Alexander Rakoczy <alex@golang.org>
This commit is contained in:
korzhao 2021-08-21 07:26:19 +08:00 committed by Alexander Rakoczy
parent 08d4cc20ca
commit d2f002cb39
1 changed files with 3 additions and 2 deletions
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5
src/time/format.go
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@ -479,7 +479,7 @@ func (t Time) String() string {
}
m1, m2 := m2/1e9, m2%1e9
m0, m1 := m1/1e9, m1%1e9
var buf []byte
buf := make([]byte, 0, 24)
buf = append(buf, " m="...)
buf = append(buf, sign)
wid := 0
@ -498,7 +498,8 @@ func (t Time) String() string {
// GoString implements fmt.GoStringer and formats t to be printed in Go source
// code.
func (t Time) GoString() string {
buf := []byte("time.Date(")
buf := make([]byte, 0, 70)
buf = append(buf, "time.Date("...)
buf = appendInt(buf, t.Year(), 0)
month := t.Month()
if January <= month && month <= December {