pxfm/gamma/
lgammaf.rs

1/*
2 * // Copyright (c) Radzivon Bartoshyk 8/2025. 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 */
29use crate::common::is_integerf;
30use crate::gamma::lgamma_rf::lgamma_coref;
31
32/// Computes log(gamma(x))
33///
34/// ulp 0.5
35pub fn f_lgammaf(x: f32) -> f32 {
36    let xb = x.to_bits();
37    if xb >= 0xffu32 << 23 || xb == 0 {
38        if x.is_infinite() {
39            return f32::INFINITY;
40        }
41        if x.is_nan() {
42            return f32::NAN;
43        }
44        if xb.wrapping_shl(1) == 0 {
45            return f32::INFINITY;
46        }
47    }
48
49    if is_integerf(x) {
50        if x == 2. || x == 1. {
51            return 0.;
52        }
53        if x.is_sign_negative() {
54            return f32::INFINITY;
55        }
56    }
57
58    lgamma_coref(x).0 as f32
59}
60
61#[cfg(test)]
62mod tests {
63    use super::*;
64
65    #[test]
66    fn test_lgammaf() {
67        assert_eq!(f_lgammaf(0.006919047), 4.969523);
68        assert_eq!(
69            f_lgammaf(0.000000000000000000000000000000000000000015425),
70            93.97255
71        );
72        assert_eq!(f_lgammaf(0.0), f32::INFINITY);
73        assert_eq!(f_lgammaf(1.7506484), -0.0842405);
74        assert_eq!(f_lgammaf(7.095007e-8), 16.461288);
75        assert!(f_lgammaf(-12.).is_infinite());
76        assert_eq!(f_lgammaf(2.), 0.);
77        assert_eq!(f_lgammaf(1.), 0.);
78        assert_eq!(f_lgammaf(0.53), 0.5156078);
79        assert_eq!(f_lgammaf(1.53), -0.11927056);
80        assert_eq!(f_lgammaf(4.53), 2.4955146);
81        assert_eq!(f_lgammaf(11.77), 16.94281);
82        assert_eq!(f_lgammaf(22.77), 47.756233);
83        assert_eq!(f_lgammaf(-0.53), 1.2684484);
84        assert_eq!(f_lgammaf(-1.53), 0.84318066);
85        assert_eq!(f_lgammaf(-4.53), -2.8570588);
86        assert_eq!(f_lgammaf(-11.77), -17.850103);
87        assert_eq!(f_lgammaf(-22.77), -49.323418);
88        assert_eq!(f_lgammaf(f32::NEG_INFINITY), f32::INFINITY);
89    }
90}
pxfm/gamma/lgammaf.rs

pxfm/gamma/
lgammaf.rs
