package main
import (
"testing"
)
const N = 4096
type T int64
var a [N]T
var globalSum T
func sumByLoopArray_a(p *[N]T) T {
var sum T
for i := 0; i < len(p); i++ {
sum += T(p[i])
}
return sum
}
func sumByLoopArray_b(p *[N]T) T {
var sum T
for i := 0; i < len(*p); i++ {
sum += T((*p)[i])
}
return sum
}
//============================================
func Benchmark_LoopArray_0a(b *testing.B) {
for i := 0; i < b.N; i++ {
var sum T
for i := 0; i < len(a); i++ {
sum += T(a[i])
}
globalSum = sum
}
}
func Benchmark_LoopArray_0b(b *testing.B) {
for i := 0; i < b.N; i++ {
var sum T
p := &a
for i := 0; i < len(p); i++ {
sum += T(p[i])
}
globalSum = sum
}
}
func Benchmark_LoopArray_1a(b *testing.B) {
for i := 0; i < b.N; i++ {
globalSum = sumByLoopArray_a(&a)
}
}
func Benchmark_LoopArray_1b(b *testing.B) {
for i := 0; i < b.N; i++ {
globalSum = sumByLoopArray_b(&a)
}
}
/* output:
$ go test . -bench=.
Benchmark_LoopArray_0a-4 300000 5248 ns/op
Benchmark_LoopArray_0b-4 300000 5240 ns/op
Benchmark_LoopArray_1a-4 500000 3942 ns/op
Benchmark_LoopArray_1b-4 300000 3936 ns/op
*/
why?
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