/rust/registry/src/index.crates.io-1949cf8c6b5b557f/pxfm-0.1.25/src/logs/logit.rs
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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 | | */ |
29 | | use crate::double_double::DoubleDouble; |
30 | | use crate::logs::{fast_log_d_to_dd, log1p_fast_dd}; |
31 | | |
32 | | /// Inverse logistic function |
33 | 0 | pub fn f_logit(x: f64) -> f64 { |
34 | 0 | let ux = x.to_bits(); |
35 | 0 | if ux >= 0x3ff0000000000000u64 || ux == 0 { |
36 | | // |x| == 0, |x| == inf, |x| == NaN, x < 0, x >= 1 |
37 | 0 | if ux.wrapping_shl(1) == 0 { |
38 | 0 | return 0.; |
39 | 0 | } |
40 | 0 | if ux == 0x3ff0000000000000u64 { |
41 | | // x == 1 |
42 | 0 | return f64::INFINITY; |
43 | 0 | } |
44 | 0 | return f64::NAN; |
45 | 0 | } |
46 | | // logit(x) = log(x/(1-p)) = log(x) - log(1-p) |
47 | 0 | let v0 = fast_log_d_to_dd(x); |
48 | 0 | let v1 = log1p_fast_dd(-x); |
49 | 0 | let product = DoubleDouble::quick_dd_sub(v0, v1); |
50 | 0 | product.to_f64() |
51 | 0 | } |
52 | | |
53 | | #[cfg(test)] |
54 | | mod tests { |
55 | | use super::*; |
56 | | |
57 | | #[test] |
58 | | fn test_logit() { |
59 | | assert_eq!(f_logit(0.70000000000007534), 0.8472978603875624); |
60 | | assert_eq!(f_logit(0.234), -1.1858610543828898); |
61 | | assert_eq!(f_logit(0.142112), -1.7978580757271523); |
62 | | assert_eq!(f_logit(0.86543), 1.8611419834868623); |
63 | | assert_eq!(f_logit(0.21312), -1.3062203716758034); |
64 | | assert_eq!(f_logit(0.128765), -1.91192270767172); |
65 | | assert_eq!(f_logit(1.), f64::INFINITY); |
66 | | assert!(f_logit(-0.00123).is_nan()); |
67 | | assert!(f_logit(f64::NAN).is_nan()); |
68 | | } |
69 | | } |