libm/math/
floor.rs

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1#![allow(unreachable_code)]
2use core::f64;
3
4const TOINT: f64 = 1. / f64::EPSILON;
5
6/// Floor (f64)
7///
8/// Finds the nearest integer less than or equal to `x`.
9#[cfg_attr(all(test, assert_no_panic), no_panic::no_panic)]
10pub fn floor(x: f64) -> f64 {
11    // On wasm32 we know that LLVM's intrinsic will compile to an optimized
12    // `f64.floor` native instruction, so we can leverage this for both code size
13    // and speed.
14    llvm_intrinsically_optimized! {
15        #[cfg(target_arch = "wasm32")] {
16            return unsafe { ::core::intrinsics::floorf64(x) }
17        }
18    }
19    #[cfg(all(target_arch = "x86", not(target_feature = "sse2")))]
20    {
21        //use an alternative implementation on x86, because the
22        //main implementation fails with the x87 FPU used by
23        //debian i386, probably due to excess precision issues.
24        //basic implementation taken from https://github.com/rust-lang/libm/issues/219
25        use super::fabs;
26        if fabs(x).to_bits() < 4503599627370496.0_f64.to_bits() {
27            let truncated = x as i64 as f64;
28            if truncated > x {
29                return truncated - 1.0;
30            } else {
31                return truncated;
32            }
33        } else {
34            return x;
35        }
36    }
37    let ui = x.to_bits();
38    let e = ((ui >> 52) & 0x7ff) as i32;
39
40    if (e >= 0x3ff + 52) || (x == 0.) {
41        return x;
42    }
43    /* y = int(x) - x, where int(x) is an integer neighbor of x */
44    let y = if (ui >> 63) != 0 { x - TOINT + TOINT - x } else { x + TOINT - TOINT - x };
45    /* special case because of non-nearest rounding modes */
46    if e < 0x3ff {
47        force_eval!(y);
48        return if (ui >> 63) != 0 { -1. } else { 0. };
49    }
50    if y > 0. { x + y - 1. } else { x + y }
51}
52
53#[cfg(test)]
54mod tests {
55    use core::f64::*;
56
57    use super::*;
58
59    #[test]
60    fn sanity_check() {
61        assert_eq!(floor(1.1), 1.0);
62        assert_eq!(floor(2.9), 2.0);
63    }
64
65    /// The spec: https://en.cppreference.com/w/cpp/numeric/math/floor
66    #[test]
67    fn spec_tests() {
68        // Not Asserted: that the current rounding mode has no effect.
69        assert!(floor(NAN).is_nan());
70        for f in [0.0, -0.0, INFINITY, NEG_INFINITY].iter().copied() {
71            assert_eq!(floor(f), f);
72        }
73    }
74}
libm/math/floor.rs

libm/math/
floor.rs
