strings.Builder.Grow calls an internal bytealg.MakeNoZero function instead of the built-in make function the old implementation called. For most cases, the built-in make function will zero the elements of the result slice, so it is often comparatively slower.
unsafe functions).
import (
"strings"
"unsafe"
)
func MakeDirtyByteSlice(n int) []byte {
var b strings.Builder
b.Grow(n)
var p = unsafe.StringData(b.String())
return unsafe.Slice(p, n)
}
package ttt
import (
"strings"
"testing"
"unsafe"
)
const Len = 20000
func init() {
println("=============== Len =", Len)
}
func MakeDirtyByteSlice(n int) []byte {
var b strings.Builder
b.Grow(n)
var p = unsafe.StringData(b.String())
return unsafe.Slice(p, n)
}
func Benchmark_MakeDirtyByteSlice(tb *testing.B) {
for range tb.N {
r = MakeDirtyByteSlice(Len)
}
}
func Benchmark_make(tb *testing.B) {
for range tb.N {
r = make([]byte, Len)
}
}
func MakeByteSlice(initialValues ...[]byte) []byte {
n := 0
for i := range initialValues {
n += len(initialValues[i])
}
n, r := 0, MakeDirtyByteSlice(n)
for _, s := range initialValues {
n += copy(r[n:], s)
}
return r
}
const N = Len / 4
var x = []byte(strings.Repeat("x", N))
var y = []byte(strings.Repeat("y", N))
var z = []byte(strings.Repeat("z", N))
var w = []byte(strings.Repeat("z", N))
var r []byte
func Benchmark_MakeByteSlice(tb *testing.B) {
for range tb.N {
r = MakeByteSlice(x, y, z, w)
}
}
func Benchmark_make_append(tb *testing.B) {
for range tb.N {
r = make([]byte, 0, Len)
r = append(r, x...)
r = append(r, y...)
r = append(r, z...)
r = append(r, w...)
}
}
$ gotv . test -bench=. -benchmem [Run]: $HOME/.cache/gotv/tag_go1.23rc1/bin/go test -bench=. -benchmem =============== Len = 4000 goos: linux goarch: amd64 pkg: example.com cpu: Intel(R) Core(TM) i5-4210U CPU @ 1.70GHz Benchmark_MakeDirtyByteSlice-4 1752531 669.5 ns/op 4096 B/op 1 allocs/op Benchmark_make-4 1268131 940.3 ns/op 4096 B/op 1 allocs/op Benchmark_MakeByteSlice-4 913239 1119 ns/op 4096 B/op 1 allocs/op Benchmark_make_append-4 1142342 1046 ns/op 4096 B/op 1 allocs/op $ gotv . test -bench=. -benchmem [Run]: $HOME/.cache/gotv/tag_go1.23rc1/bin/go test -bench=. -benchmem =============== Len = 20000 goos: linux goarch: amd64 pkg: example.com cpu: Intel(R) Core(TM) i5-4210U CPU @ 1.70GHz Benchmark_MakeDirtyByteSlice-4 628150 1863 ns/op 20480 B/op 1 allocs/op Benchmark_make-4 320997 3404 ns/op 20480 B/op 1 allocs/op Benchmark_MakeByteSlice-4 262684 4213 ns/op 20480 B/op 1 allocs/op Benchmark_make_append-4 246081 4525 ns/op 20480 B/op 1 allocs/op
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