pxfm/err/
inverfcf.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::err::inverff::erfinv_core;
30
31/// Complementary inverse error function
32///
33/// Max ulp 0.5
34pub fn f_erfcinvf(x: f32) -> f32 {
35    let ix = x.to_bits();
36    let ux = ix.wrapping_shl(1);
37    if ix >= 0x4000_0000u32 || ux == 0 {
38        if x.is_infinite() {
39            return f32::INFINITY;
40        }
41        if ux == 0 {
42            return f32::INFINITY;
43        }
44
45        if ix == 0x3f80_0000u32 {
46            return 0.;
47        }
48        // x > 2
49        if ix == 0x4000_0000u32 {
50            // x == 2.
51            return f32::NEG_INFINITY;
52        }
53        return f32::NAN; // x == NaN, x < 0
54    }
55
56    let z = x as f64;
57    static SIGN: [f32; 2] = [1.0, -1.0];
58    // inferfc(x) = -inverf(1-x)
59    // ax doesn't need to be extremely accurate,
60    // it's just boundary detection so will do subtraction in f32
61    erfinv_core(1. - z, (1. - x).abs().to_bits(), SIGN[(x > 1.) as usize])
62}
63
64#[cfg(test)]
65mod tests {
66    use super::f_erfcinvf;
67
68    #[test]
69    fn m_test() {
70        assert_eq!(f_erfcinvf(2.), f32::NEG_INFINITY);
71        assert!(f_erfcinvf(-1.).is_nan());
72        assert_eq!(f_erfcinvf(0.), f32::INFINITY);
73        assert!(f_erfcinvf(2.1).is_nan());
74        assert_eq!(f_erfcinvf(0.5), 0.47693628);
75        assert_eq!(f_erfcinvf(1.5), -0.47693628);
76        assert_eq!(f_erfcinvf(0.002), 2.1851242);
77        assert_eq!(f_erfcinvf(1.002), -0.0017724329);
78        assert!(f_erfcinvf(f32::NAN).is_nan());
79    }
80}
pxfm/err/inverfcf.rs

pxfm/err/
inverfcf.rs
