std::intrinsics

Function ctlz

const: 1.40.0 · source
pub const extern "rust-intrinsic" fn ctlz<T>(x: T) -> u32
where T: Copy,
🔬This is a nightly-only experimental API. (core_intrinsics)
Expand description

Returns the number of leading unset bits (zeroes) in an integer type T.

Note that, unlike most intrinsics, this is safe to call; it does not require an unsafe block. Therefore, implementations must not require the user to uphold any safety invariants.

The stabilized versions of this intrinsic are available on the integer primitives via the leading_zeros method. For example, u32::leading_zeros

§Examples

#![feature(core_intrinsics)]

use std::intrinsics::ctlz;

let x = 0b0001_1100_u8;
let num_leading = ctlz(x);
assert_eq!(num_leading, 3);

An x with value 0 will return the bit width of T.

#![feature(core_intrinsics)]

use std::intrinsics::ctlz;

let x = 0u16;
let num_leading = ctlz(x);
assert_eq!(num_leading, 16);