half/
leading_zeros.rs

1// https://doc.rust-lang.org/std/primitive.u16.html#method.leading_zeros
2
3#[cfg(not(any(all(
4    target_arch = "spirv",
5    not(all(
6        target_feature = "IntegerFunctions2INTEL",
7        target_feature = "SPV_INTEL_shader_integer_functions2"
8    ))
9))))]
10#[inline]
11pub(crate) const fn leading_zeros_u16(x: u16) -> u32 {
12    x.leading_zeros()
13}
14
15#[cfg(all(
16    target_arch = "spirv",
17    not(all(
18        target_feature = "IntegerFunctions2INTEL",
19        target_feature = "SPV_INTEL_shader_integer_functions2"
20    ))
21))]
22#[inline]
23pub(crate) const fn leading_zeros_u16(x: u16) -> u32 {
24    leading_zeros_u16_fallback(x)
25}
26
27#[cfg(any(
28    test,
29    all(
30        target_arch = "spirv",
31        not(all(
32            target_feature = "IntegerFunctions2INTEL",
33            target_feature = "SPV_INTEL_shader_integer_functions2"
34        ))
35    )
36))]
37#[inline]
38const fn leading_zeros_u16_fallback(mut x: u16) -> u32 {
39    use crunchy::unroll;
40    let mut c = 0;
41    let msb = 1 << 15;
42    unroll! { for i in 0 .. 16 {
43        if x & msb == 0 {
44            c += 1;
45        } else {
46            return c;
47        }
48        #[allow(unused_assignments)]
49        if i < 15 {
50            x <<= 1;
51        }
52    }}
53    c
54}
55
56#[cfg(test)]
57mod test {
58
59    #[test]
60    fn leading_zeros_u16_fallback() {
61        for x in [44, 97, 304, 1179, 23571] {
62            assert_eq!(super::leading_zeros_u16_fallback(x), x.leading_zeros());
63        }
64    }
65}
half/leading_zeros.rs

half/
leading_zeros.rs
