libm/math/
trunc.rs

1use core::f64;
2
3#[cfg_attr(all(test, assert_no_panic), no_panic::no_panic)]
4pub fn trunc(x: f64) -> f64 {
5    // On wasm32 we know that LLVM's intrinsic will compile to an optimized
6    // `f64.trunc` native instruction, so we can leverage this for both code size
7    // and speed.
8    llvm_intrinsically_optimized! {
9        #[cfg(target_arch = "wasm32")] {
10            return unsafe { ::core::intrinsics::truncf64(x) }
11        }
12    }
13    let x1p120 = f64::from_bits(0x4770000000000000); // 0x1p120f === 2 ^ 120
14
15    let mut i: u64 = x.to_bits();
16    let mut e: i64 = (i >> 52 & 0x7ff) as i64 - 0x3ff + 12;
17    let m: u64;
18
19    if e >= 52 + 12 {
20        return x;
21    }
22    if e < 12 {
23        e = 1;
24    }
25    m = -1i64 as u64 >> e;
26    if (i & m) == 0 {
27        return x;
28    }
29    force_eval!(x + x1p120);
30    i &= !m;
31    f64::from_bits(i)
32}
33
34#[cfg(test)]
35mod tests {
36    #[test]
37    fn sanity_check() {
38        assert_eq!(super::trunc(1.1), 1.0);
39    }
40}