Swap every two bits in bytes

Swap all the pair of bits in a byte. Before swapping: 11-10-11-01 After swapping: 11-01-11-10
Examples:

Input  : 00000010
Output : 00000001

Input  : 00000100
Output : 00001000

Approach:
x = ((x & 0x55555555) >> 1) | ((x & 0xAAAAAAAA) <> 1 extracts the high bit position and shifts it to the low bit position.
Similarly the expression (x & 0xAAAAAAAA) << 1 extracts the low bit from each pair and shifts it to the high bit position.
The two parts are then combined using bitwise-OR.

x= 00011010
((x & 0xAAAAAAAA) >> 1) = 00001010 >> 1
                        = 00000101
((x & 0x55555555) << 1) = 00010000 <> 1) | ((x & 0x55555555) << 1) = 00100101

Below is the implementation of the above idea:

C++

// C++ program to swap every two bits in a byte.
#include<bits/stdc++.h>
using namespace std;

unsigned int swapBitsInPair(unsigned int x)
{
    // Extracting the high bit shift it to lowbit
    // Extracting the low bit shift it to highbit
    return ((x & 0xAAAAAAAA) >> 1) | 
            ((x & 0x55555555) << 1);    
}

/* Driver function to test above function */
int main()
{
    unsigned int x = 4; 
    cout << swapBitsInPair(x);    
    return 0;
}

// This code is contributed by Kasina Dheeraj.

Java

// Java program to swap every 
// two bits in a byte.
import java.util.*;

class GFG
{
    static int swapBitsInPair( int x)
    {
        // Extracting the high bit shift it to lowbit
        // Extracting the low bit shift it to highbit
        return ((x & 0xAAAAAAAA) >> 1) | 
                ((x & 0x55555555) << 1); 
    }

    // Driver Function
    public static void main(String[] args)
    {
    int x = 4; 
    System.out.print(swapBitsInPair(x)); 
    }
}

// This code is contributed by Gitanjali.

Python3

# Python program to swap every 
# two bits in a byte.

import math

def swapBitsInPair( x):

    # Extracting the high bit shift it to lowbit
    # Extracting the low bit shift it to highbit
    return ((x & 0xAAAAAAAA) >> 1) or ((x & 0x55555555) << 1)

# driver Function
x = 4; 
print(swapBitsInPair(x)) 

# This code is contributed by Gitanjali.

// C# program to swap every two bits in a byte.
using System;

public class GFG{

    static uint swapBitsInPair(uint x)
    {
        // Extracting the high bit shift it to lowbit
        // Extracting the low bit shift it to highbit
        return ((x & 0xAAAAAAAA) >> 1) | 
                ((x & 0x55555555) << 1); 
    }
    
    // Driver function to test above function 
    static public void Main () {
        
        uint x = 4; 
        
        Console.WriteLine(swapBitsInPair(x)); 
    }
}

// This code is contributed by vt_m.

PHP

<?php
// PHP program to swap every
// two bits in a byte.

function swapBitsInPair($x)
{
    
    // Extracting the high bit 
    // shift it to lowbit
    // Extracting the low bit
    // shift it to highbit
    return (($x & 0xAAAAAAAA) >> 1) | 
           (($x & 0x55555555) << 1); 
}

    // Driver Code
    $x = 4; 
    echo swapBitsInPair($x); 

// This code is contributed by mits 
?>

JavaScript

<script>

// java script program to swap every
// two bits in a byte.

function swapBitsInPair(x)
{
    
    // Extracting the high bit 
    // shift it to lowbit
    // Extracting the low bit
    // shift it to highbit
    return ((x & 0xAAAAAAAA) >> 1) | 
           ((x & 0x55555555) << 1); 
}

    // Driver Code
    let x = 4; 
    document.write( swapBitsInPair(x));

// This code is contributed by sravan kumar
</script>

Output:

Time Complexity: O(1)

Space Complexity: O(1)

Reference:
https://stackoverflow.com/questions/4788799/swap-every-pair-of-bits-in-byte

Swap every two bits in bytes

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