Popcount, Hamming, POPCNT, Population count, Golang, https://play.golang.org/p/M2nxXCyrd7

popcount.go

package main

import (
	"fmt"
	"testing"
	"time"
)

const N = 8

var a [1 << N]byte

func init() {
	for i := range a {
		var n byte
		for x := i; x != 0; x >>= 1 {
			if x&1 != 0 {
				n++
			}
		}
		a[i] = n
	}
}

func popcount(x uint64) (n byte) {
	return a[byte(x>>0*N)] +
		a[byte(x>>1*N)] +
		a[byte(x>>2*N)] +
		a[byte(x>>3*N)] +
		a[byte(x>>4*N)] +
		a[byte(x>>5*N)] +
		a[byte(x>>6*N)] +
		a[byte(x>>7*N)]
}

func BenchmarkPopcount(b *testing.B) {
	x := uint64(0x73fa55623a30abed)
	for i := b.N; i > 0; i-- {
		popcount(x)
	}
}

func main() {
	res := testing.Benchmark(BenchmarkPopcount)
	fmt.Println(res.N, res.T, time.Duration(int64(res.T)/int64(res.N)))
}