How to Reverse Bits in a Byte Using a Simple C/C Function?

Simplest Method to Reverse Bits in a Byte in C/C

Reversing the order of bits in a byte can be achieved through various techniques. Among these methods, the one presented below offers the simplest implementation for developers:

unsigned char reverse(unsigned char b) {
   b = (b &amp; 0xF0) >> 4 | (b &amp; 0x0F) << 4;
   b = (b &amp; 0xCC) >> 2 | (b &amp; 0x33) << 2;
   b = (b &amp; 0xAA) >> 1 | (b &amp; 0x55) << 1;
   return b;
}

Explanation:

The function reverses the order of bits in a byte by applying the bitwise operators &, |, >>, and <<. The following operations are performed:

1. The first line swaps the left four bits with the right four bits by shifting the left nibble right by 4 bits and the right nibble left by 4 bits, and then combining them with the bitwise OR operator.
2. The second line swaps adjacent pairs of bits by shifting the even-indexed bits right by 2 bits and the odd-indexed bits left by 2 bits, followed by a bitwise OR.
3. The third line swaps adjacent single bits by shifting the bits at positions 1, 3, 5, and 7 right by 1 bit and those at positions 2, 4, 6, and 8 left by 1 bit, followed by a bitwise OR.

This sequence of operations effectively reverses the order of bits in a byte.

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