比较两个数组中的位

Question

I've got stuck with ex4.1 for the book which says:
Write a function that counts the number of bits that are different in two SHA256 hashes.

The partial solution I came up with is pasted below, but it's wrong - it counts number of different bytes not bits. Could you please point me in the right direction?

package main

import (
    "crypto/sha256"
    "fmt"
)

var s1 string = "unodostresquatro"
var s2 string = "UNODOSTRESQUATRO"
var h1 = sha256.Sum256([]byte(s1))
var h2 = sha256.Sum256([]byte(s2))

func main() {
    fmt.Printf("s1: %s h1: %X h1 type: %T
", s1, h1, h1) 
    fmt.Printf("s2: %s h2: %X h2 type: %T
", s2, h2, h2) 
    fmt.Printf("Number of different bits: %d
", 8 * DifferentBits(h1, h2))
}

func DifferentBits(c1 [32]uint8, c2 [32]uint8) int {
    var counter int 
    for x := range c1 {
        if c1[x] != c2[x] {
            counter += 1
        }
    }   
    return counter

}

Answer 1

The Go Programming Language

Alan A. A. Donovan · Brian W.Kernighan

Exercise 4.1: Write a function that counts the number of bits that are different in two SHA256 hashes.

---

The C Programming Language

Brian W.Kernighan · Dennis M. Ritchie

Exercise 2-9. In a two's complement number system, x &= (x-1) deletes the rightmost 1-bit in x. Use this observation to write a faster version of bitcount.

---

Bit Twiddling Hacks

Sean Eron Anderson

Counting bits set, Brian Kernighan's way

unsigned int v; // count the number of bits set in v
unsigned int c; // c accumulates the total bits set in v
for (c = 0; v; c++)
{
  v &= v - 1; // clear the least significant bit set
}

---

For exercise 4.1, you are counting the number of bytes that are different. Count the number of bits that are different. For example,

package main

import (
    "crypto/sha256"
    "fmt"
)

func BitsDifference(h1, h2 *[sha256.Size]byte) int {
    n := 0
    for i := range h1 {
        for b := h1[i] ^ h2[i]; b != 0; b &= b - 1 {
            n++
        }
    }
    return n
}

func main() {
    s1 := "unodostresquatro"
    s2 := "UNODOSTRESQUATRO"
    h1 := sha256.Sum256([]byte(s1))
    h2 := sha256.Sum256([]byte(s2))
    fmt.Println(BitsDifference(&h1, &h2))
}

Output:

139