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)]
# #![allow(internal_features)]

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)]
# #![allow(internal_features)]

use std::intrinsics::ctlz;

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