std::bits

A small bit-manipulation and byte-order helper subset is implemented in std/bits.slk for the current backend subset.

std::bits provides common bit “twiddling” helpers:

• byte swaps (bswap_*),
• bit rotations (rotl_*, rotr_*),
• and bit counts (popcount_*, clz_*, ctz_*).

See also:

• operators (bitwise operators and shift semantics)
• networking (std::net byte-order helpers built on the hosted baseline)

Exported API#

module std::bits;

export pure fn bswap_u16 (x: u16) -> u16;
export pure fn bswap_u32 (x: u32) -> u32;
export pure fn bswap_u64 (x: u64) -> u64;

export pure fn rotl_u32 (v: u32, shift: u32) -> u32;
export pure fn rotr_u32 (v: u32, shift: u32) -> u32;

export pure fn rotl_u64 (v: u64, shift: u32) -> u64;
export pure fn rotr_u64 (v: u64, shift: u32) -> u64;

export pure fn popcount_u32 (x: u32) -> u32;
export pure fn clz_u32 (x: u32) -> u32;
export pure fn ctz_u32 (x: u32) -> u32;

export pure fn popcount_u64 (x: u64) -> u32;
export pure fn clz_u64 (x: u64) -> u32;
export pure fn ctz_u64 (x: u64) -> u32;

Rotation semantics#

• rotl_u32 / rotr_u32 mask the shift amount by 31.
• rotl_u64 / rotr_u64 mask the shift amount by 63.

This means all shift values are valid and rotations do not rely on any target-specific shift masking behavior.

Count semantics#

• popcount_* counts the number of 1-bits.
• clz_* counts leading zeros.
• ctz_* counts trailing zeros.

For clz_* and ctz_*, when the input is 0 the function returns the full bit width (32 or 64).

Example#

import std::bits;

fn main () -> int {
  let x: u32 = std::bits::rotl_u32(1, 5);
  if x != ((1 as u32) << 5) {
    return 1;
  }

  let y: u64 = std::bits::bswap_u64(4660); // 0x0000_0000_0000_1234
  if y == 0 {
    return 2;
  }

  return 0;
}