pxfm/hyperbolic/
atanhf.rs

1/*
2 * // Copyright (c) Radzivon Bartoshyk 7/2025. 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::f_fmla;
30use crate::hyperbolic::asinhf::log_eval;
31use crate::polyeval::f_polyeval6;
32
33/// Hyperbolic atan
34///
35/// Max ULP 0.5
36#[inline]
37pub fn f_atanhf(x: f32) -> f32 {
38    let x_abs = x.to_bits() & 0x7fff_ffff;
39
40    // |x| >= 1.0
41    if x_abs >= 0x3F80_0000u32 {
42        if x.is_nan() {
43            return x;
44        }
45        // |x| == 1.0
46        return if x_abs == 0x3F80_0000u32 {
47            if x.is_sign_positive() {
48                f32::INFINITY
49            } else {
50                f32::NEG_INFINITY
51            }
52        } else {
53            f32::NAN
54        };
55    }
56
57    // |x| < ~0.10
58    if x_abs <= 0x3dcc_0000u32 {
59        // |x| <= 2^-26
60        if x_abs <= 0x3280_0000u32 {
61            return if x_abs == 0 {
62                x
63            } else {
64                (x as f64 + f64::from_bits(0x3fd5555555555555) * x as f64 * x as f64 * x as f64)
65                    as f32
66            };
67        }
68
69        let xdbl = x as f64;
70        let x2 = xdbl * xdbl;
71        // Pure Taylor series.
72        let pe = f_polyeval6(
73            x2,
74            0.0,
75            f64::from_bits(0x3fd5555555555555),
76            f64::from_bits(0x3fc999999999999a),
77            f64::from_bits(0x3fc2492492492492),
78            f64::from_bits(0x3fbc71c71c71c71c),
79            f64::from_bits(0x3fb745d1745d1746),
80        );
81        return f_fmla(xdbl, pe, xdbl) as f32;
82    }
83    let xdbl = x as f64;
84    (0.5 * log_eval((xdbl + 1.0) / (xdbl - 1.0))) as f32
85}
86
87#[cfg(test)]
88mod tests {
89    use super::*;
90    #[test]
91    fn test_atanhf() {
92        assert_eq!(f_atanhf(0.0), 0.0);
93        assert_eq!(f_atanhf(1.0), f32::INFINITY);
94        assert!(f_atanhf(-1.5).is_nan());
95        assert_eq!(f_atanhf(0.25), 0.25541282);
96        assert_eq!(f_atanhf(0.124121), 0.12476436);
97    }
98}
pxfm/hyperbolic/atanhf.rs

pxfm/hyperbolic/
atanhf.rs
