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}
75