[go-nuts] Boxing bytes is faster than boxing integers within [0. 255]. Why?

[tapi...@gmail.com]

Different optimizations are applied for them?

The benchmark:

package main

import "testing"

func BoxByte(b byte) interface{} {
    return b
}

func BoxInt64(i int64) interface{} {
    return i
}

var b0, b1, b2 byte = 0, 128, 255
var d, e, f interface{}
func Benchmark_BoxByte(b *testing.B) {
    for i := 0; i < b.N; i++ {
        d = BoxByte(b0)
        e = BoxByte(b1)
        f = BoxByte(b2)
    }
}

var i0s, i1s, i2s int64 = 0, 128, 255
var m, n, o interface{}
func Benchmark_BoxInt64_Small(b *testing.B) {
    for i := 0; i < b.N; i++ {
        m = BoxInt64(i0s)
        n = BoxInt64(i1s)
        o = BoxInt64(i2s)
    }
}

var i0b, i1b, i2b int64 = 256, 1024, 65536
var x, y, z interface{}
func Benchmark_BoxInt64_Large(b *testing.B) {
    for i := 0; i < b.N; i++ {
        x = BoxInt64(i0b)
        y = BoxInt64(i1b)
        z = BoxInt64(i2b)
    }
}

The result:

$ go test -bench=. 
goos: linux
goarch: amd64
pkg: a.b/c/ttt
cpu: Intel(R) Core(TM) i5-4210U CPU @ 1.70GHz
Benchmark_BoxByte-4              429777054             2.681 ns/op
Benchmark_BoxInt64_Small-4       125588462             9.527 ns/op
Benchmark_BoxInt64_Large-4       18019028            63.75 ns/op


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