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#

// 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: 

8

Time Complexity: O(1)

Space Complexity: O(1)

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

This article is contributed by Saumya and improved by Kasina Dheeraj .If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

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