# Swap every two bits in bytes

• Difficulty Level : Medium
• Last Updated : 22 May, 2022

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` `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

 `> 1) | ` `           ``((``\$x` `& 0x55555555) << 1); ` `}`   `    ``// Driver Code` `    ``\$x` `= 4; ` `    ``echo` `swapBitsInPair(``\$x``); `   `// This code is contributed by mits ` `?>`

## Javascript

 ``

Output:

`8`

Time Complexity: O(1)

Space Complexity: O(1)

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.