How do you extract individual bits from a byte in Golang?

Extracting Bits from a Byte in Golang

Many tasks, such as calculating the Hamming distance between bytes, require access to individual bits within the byte. However, the built-in Golang packages do not provide a direct function for this purpose.

Visual Representation vs. Bitwise Operations

One approach is to use fmt.Sprintf("b", ...) to print a binary representation of the byte, as suggested by several answers online. However, this approach merely provides a visual representation of the bits, making it unsuitable for operations like bitwise comparisons.

Bit Masking for Retrieving Bits

To perform bitwise operations, we can utilize the bitwise AND operator (&) along with masking. For instance, to obtain the n^th bit of a byte (where n starts from 1), we create a mask m where only the n^th bit is set to 1. This mask can be obtained as m = 2**(n-1). By bitwise ANDing the byte with the mask, we can determine if the n^th bit is set:

if (b & m) != 0 {
    // nth bit is set to 1
}

Sample Code

The following code demonstrates the use of bit masking to extract bits from a byte and calculate the Hamming distance:

<code class="go">package main

import "fmt"

func hamming(a, b []byte) (int, error) {
    if len(a) != len(b) {
        return 0, errors.New("a, b are not the same length")
    }

    diff := 0
    for i := 0; i < len(a); i++ {
        b1 := a[i]
        b2 := b[i]
        for j := 0; j < 8; j++ {
            // Create a mask to check the (j+1)th bit
            mask := byte(1 << uint(j))
            if (b1 & mask) != (b2 & mask) {
                diff++
            }
        }
    }
    return diff, nil
}

func main() {
    // Example: Compute the Hamming distance between two bytes
    b1 := byte(255) // 11111111
    b2 := byte(0) // 00000000
    distance, err := hamming([]byte{b1}, []byte{b2})
    if err != nil {
        fmt.Println(err)
        return
    }
    fmt.Println("Hamming distance:", distance) // Outputs: 8
}</code>

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