count_diff_bits.go

package main

import "fmt"

var bits [256]int

func init() {
	for i := range bits {
		bits[i] = bits[i>>1] + i&0x1
	}
}

func main() {
	var a, b [32]byte

	a[0], a[31] = 1, 1

	fmt.Println(countDiffBits(a, b))
}

func countDiffBits(a, b [32]byte) (res int) {
	for i := 0; i < 32; i++ {
		res += bits[int(a[i]^b[i])]
	}
	return
}

Live code - https://play.golang.org/p/O7ZOe_3Emy

Output:

2