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/*
* // Copyright (c) Radzivon Bartoshyk 6/2025. All rights reserved.
* //
* // Redistribution and use in source and binary forms, with or without modification,
* // are permitted provided that the following conditions are met:
* //
* // 1. Redistributions of source code must retain the above copyright notice, this
* // list of conditions and the following disclaimer.
* //
* // 2. Redistributions in binary form must reproduce the above copyright notice,
* // this list of conditions and the following disclaimer in the documentation
* // and/or other materials provided with the distribution.
* //
* // 3. Neither the name of the copyright holder nor the names of its
* // contributors may be used to endorse or promote products derived from
* // this software without specific prior written permission.
* //
* // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
* // AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* // IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
* // DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
* // FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* // DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
* // SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
* // CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
* // OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
use crate::common::{f_fmla, f_fmlaf};
/// Hyperbolic tangent
///
/// Max found ULP 0.4999994
#[inline]
pub fn f_tanhf(x: f32) -> f32 {
let z = x as f64;
let t = x.to_bits();
let ux = t;
let e = ux.wrapping_shr(23) & 0xff;
if e == 0xff {
if ux << 9 != 0 {
return x + x;
} // x = nan
const IR: [f32; 2] = [1.0, -1.0];
return IR[ux.wrapping_shr(31) as usize]; // x = +-inf
}
if e < 115 {
// |x| < 2^-13
if e < 102 {
// |x| < 2^-26
if ux.wrapping_shl(1) == 0 {
return x;
}
let res = f_fmlaf(-x, x.abs(), x);
return res;
}
let x2 = x * x;
return f_fmlaf(x, -f64::from_bits(0x3fd5555560000000) as f32 * x2, x);
}
if ux.wrapping_shl(1) > (0x41102cb3u32 << 1) {
return f32::copysign(1.0, x) - f32::copysign(f64::from_bits(0x3e60000000000000) as f32, x);
}
let z2 = z * z;
let z4 = z2 * z2;
let z8 = z4 * z4;
const CN: [u64; 8] = [
0x3ff0000000000000,
0x3fc30877b8b72d33,
0x3f7694aa09ae9e5e,
0x3f14101377abb729,
0x3e9e0392b1db0018,
0x3e12533756e546f7,
0x3d6d62e5abe6ae8a,
0x3c9b06be534182de,
];
const CD: [u64; 8] = [
0x3ff0000000000000,
0x3fded99131b0ebea,
0x3fa0d27ed6c95a69,
0x3f47cbdaca0e9fcc,
0x3edb4e60b892578e,
0x3e5a6f707c5c71ab,
0x3dc35a8b6e2cd94c,
0x3d0ca8230677aa01,
];
let mut n0 = f_fmla(z2, f64::from_bits(CN[1]), f64::from_bits(CN[0]));
let n2 = f_fmla(z2, f64::from_bits(CN[3]), f64::from_bits(CN[2]));
let mut n4 = f_fmla(z2, f64::from_bits(CN[5]), f64::from_bits(CN[4]));
let n6 = f_fmla(z2, f64::from_bits(CN[7]), f64::from_bits(CN[6]));
n0 = f_fmla(z4, n2, n0);
n4 = f_fmla(z4, n6, n4);
n0 = f_fmla(z8, n4, n0);
let mut d0 = f_fmla(z2, f64::from_bits(CD[1]), f64::from_bits(CD[0]));
let d2 = f_fmla(z2, f64::from_bits(CD[3]), f64::from_bits(CD[2]));
let mut d4 = f_fmla(z2, f64::from_bits(CD[5]), f64::from_bits(CD[4]));
let d6 = f_fmla(z2, f64::from_bits(CD[7]), f64::from_bits(CD[6]));
d0 = f_fmla(z4, d2, d0);
d4 = f_fmla(z4, d6, d4);
d0 = f_fmla(z8, d4, d0);
let r = z * n0 / d0;
r as f32
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn test_tanhf() {
assert_eq!(f_tanhf(-0.5), -0.46211717);
assert_eq!(f_tanhf(0.5), 0.46211717);
assert_eq!(f_tanhf(7.), 0.99999833);
}
}