pxfm/logs/
logitf.rs

1/*
2 * // Copyright (c) Radzivon Bartoshyk 9/2025. 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::logs::log1pf::{core_log1pf, core_logf};
30
31/// Inverse logistic function
32pub fn f_logitf(x: f32) -> f32 {
33    let ux = x.to_bits();
34    if ux >= 0x3f80_0000u32 || ux == 0 {
35        // |x| == 0, |x| == inf, |x| == NaN, x < 0, x >= 1
36        if ux.wrapping_shl(1) == 0 {
37            return 0.;
38        }
39        if ux == 0x3f80_0000u32 {
40            // x == 1
41            return f32::INFINITY;
42        }
43        return f32::NAN;
44    }
45    // logit(x) = log(x/(1-p)) = log(x) - log(1-p)
46    let v0 = core_logf(x as f64);
47    let v1 = core_log1pf(-x);
48    (v0 - v1) as f32
49}
50
51#[cfg(test)]
52mod tests {
53    use super::*;
54
55    #[test]
56    fn test_logit() {
57        assert_eq!(f_logitf(0.234), -1.1858611);
58        assert_eq!(f_logitf(0.142112), -1.7978581);
59        assert_eq!(f_logitf(0.86543), 1.8611419);
60        assert_eq!(f_logitf(0.21312), -1.3062204);
61        assert_eq!(f_logitf(0.128765), -1.9119227);
62        assert_eq!(f_logitf(1.), f32::INFINITY);
63        assert!(f_logitf(-0.00123).is_nan());
64        assert!(f_logitf(f32::NAN).is_nan());
65    }
66}
pxfm/logs/logitf.rs

pxfm/logs/
logitf.rs
