libm/math/
ceil.rs

1#![allow(unreachable_code)]
2use core::f64;
3
4const TOINT: f64 = 1. / f64::EPSILON;
5
6/// Ceil (f64)
7///
8/// Finds the nearest integer greater than or equal to `x`.
9#[cfg_attr(all(test, assert_no_panic), no_panic::no_panic)]
10pub fn ceil(x: f64) -> f64 {
11    // On wasm32 we know that LLVM's intrinsic will compile to an optimized
12    // `f64.ceil` 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::ceilf64(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, probablly 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 u: u64 = x.to_bits();
38    let e: i64 = (u >> 52 & 0x7ff) as i64;
39    let y: f64;
40
41    if e >= 0x3ff + 52 || x == 0. {
42        return x;
43    }
44    // y = int(x) - x, where int(x) is an integer neighbor of x
45    y = if (u >> 63) != 0 {
46        x - TOINT + TOINT - x
47    } else {
48        x + TOINT - TOINT - x
49    };
50    // special case because of non-nearest rounding modes
51    if e < 0x3ff {
52        force_eval!(y);
53        return if (u >> 63) != 0 { -0. } else { 1. };
54    }
55    if y < 0. {
56        x + y + 1.
57    } else {
58        x + y
59    }
60}
61
62#[cfg(test)]
63mod tests {
64    use super::*;
65    use core::f64::*;
66
67    #[test]
68    fn sanity_check() {
69        assert_eq!(ceil(1.1), 2.0);
70        assert_eq!(ceil(2.9), 3.0);
71    }
72
73    /// The spec: https://en.cppreference.com/w/cpp/numeric/math/ceil
74    #[test]
75    fn spec_tests() {
76        // Not Asserted: that the current rounding mode has no effect.
77        assert!(ceil(NAN).is_nan());
78        for f in [0.0, -0.0, INFINITY, NEG_INFINITY].iter().copied() {
79            assert_eq!(ceil(f), f);
80        }
81    }
82}