pxfm/square_root/
sqrtf.rs

1/*
2 * // Copyright (c) Radzivon Bartoshyk 4/2025. All rights reserved.
3 * //
4 * // Redistribution and use in source and binary forms, with or without modification,
5 * // are permitted provided that the following conditions are met:
6 * //
7 * // 1.  Redistributions of source code must retain the above copyright notice, this
8 * // list of conditions and the following disclaimer.
9 * //
10 * // 2.  Redistributions in binary form must reproduce the above copyright notice,
11 * // this list of conditions and the following disclaimer in the documentation
12 * // and/or other materials provided with the distribution.
13 * //
14 * // 3.  Neither the name of the copyright holder nor the names of its
15 * // contributors may be used to endorse or promote products derived from
16 * // this software without specific prior written permission.
17 * //
18 * // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
19 * // AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
20 * // IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
21 * // DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
22 * // FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
23 * // DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
24 * // SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
25 * // CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
26 * // OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
27 * // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
28 */
29
30/// Computes Square root.
31/// Most of CPU have built-in instruction with higher precision,
32/// prefer use this only for const contexts.
33#[inline]
34pub const fn sqrtf(d: f32) -> f32 {
35    let mut q = 0.5f32;
36
37    let mut d = if d < 0f32 { f32::NAN } else { d };
38
39    if d < 5.2939559203393770e-23f32 {
40        d *= 1.8889465931478580e+22f32;
41        q = 7.2759576141834260e-12f32;
42    }
43
44    if d > 1.8446744073709552e+19f32 {
45        d *= 5.4210108624275220e-20f32;
46        q = 4294967296.0f32;
47    }
48
49    // http://en.wikipedia.org/wiki/Fast_inverse_square_root
50    let mut x = f32::from_bits(0x5f375a86 - ((d + 1e-45).to_bits() >> 1)) as f64;
51
52    x = x * (1.5 - 0.5 * (d as f64) * x * x);
53    x = x * (1.5 - 0.5 * (d as f64) * x * x);
54    x = x * (1.5 - 0.5 * (d as f64) * x * x) * (d as f64);
55
56    let d2 = ((d as f64) + x * x) * (1. / x);
57
58    if d.is_infinite() {
59        return f32::INFINITY;
60    }
61    (d2 * q as f64) as f32
62}
63
64#[cfg(test)]
65mod tests {
66
67    use super::*;
68
69    #[test]
70    fn sqrtf_test() {
71        assert!(
72            (sqrtf(4f32) - 2f32).abs() < 1e-6,
73            "Invalid result {}",
74            sqrtf(4f32)
75        );
76        assert!(
77            (sqrtf(9f32) - 3f32).abs() < 1e-6,
78            "Invalid result {}",
79            sqrtf(9f32)
80        );
81        assert_eq!(sqrtf(4.), 2.);
82        assert_eq!(sqrtf(9.), 3.);
83        assert_eq!(sqrtf(16.), 4.);
84        assert_eq!(sqrtf(25.), 5.);
85    }
86}
pxfm/square_root/sqrtf.rs

pxfm/square_root/
sqrtf.rs
