bit

The bit module houses Vex's fundamental low-level bit manipulation primitives. These are essential for custom algorithms, specialized data structures, network protocols, compress/decompress paths, and manual CPU-aligned math.

Vex's Bit.* functions map directly to single CPU instructions (e.g. POPCNT, LZCNT, TZCNT on x86, or RBIT on ARM) ensuring there are no function call overheads at runtime.

Core Operations

Population Count

Counts the total number of set 1 bits in a binary representation.

let val: u32 = 0b1011;
println(Bit.popcnt32(val)); // 3

Maps to llvm.ctpop.i32

Leading & Trailing Zeros

Calculates the number of 0 bits preceding the highest set bit, or following the lowest set bit. Helpful for finding alignment offsets and mask calculation.

Bit.lzcnt32(0b0100) // 29
Bit.tzcnt64(0b1000) // 3

Endian Reversal (Byte Swap)

Reverses the endianness of an integer. Required for networking stacks or unpacking foreign buffer structures.

let rev = Bit.bswap32(0x12345678); // 0x78563412

Rotating Values

Rotates bits left or right, carrying them over to the overflow bounds. Crucial in hashing configurations (e.g. xxHash, WyHash).

Bit.rotl64(val, 3);
Bit.rotr32(val, 2);

Integration with Tensors

Like the Math.* built-ins, Bit.* primitives can be automatically promoted to SIMD vector executions when called on Tensor<T, N> structures!