Endianness Byte-Swap Converter

Formula

How this is calculated

Enter a hexadecimal value and choose its width: 16, 32, or 64 bits. The value is first cleaned (an optional 0x prefix, spaces, and underscores are removed) and then zero-padded on the left to the full width, so a 32-bit input always becomes 8 hex digits (4 bytes). The string is split into w/8 bytes, each one being a pair of hex digits.

Byte swapping simply reverses the order of those bytes. For example, the 32-bit value 0x12345678 has bytes [12, 34, 56, 78]; reversing them gives [78, 56, 34, 12], i.e. 0x78563412. This is exactly the bswap operation used when moving data between big-endian and little-endian systems, since the two orderings store the most-significant and least-significant bytes at opposite ends.

The original and swapped decimal values are computed with 64-bit-safe integer arithmetic, and the per-byte mapping shows how each source byte position moves to its destination (position i goes to position n-1-i). Note that the swap is its own inverse: applying it twice returns the original value. Inputs with more hex digits than the chosen width, or with non-hex characters, are rejected.