/*

 * // 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;

#[inline(always)]

fn atanpif_gen_impl<Q: Fn(f64, f64, f64) -> f64>(x: f32, fma: Q) -> f32 {

    let t = x.to_bits();

    let e: i32 = ((t >> 23) & 0xff) as i32;

    let gt = e >= 127;

    if e > 127 + 24 {

        // |x| >= 2^25

        let f = f32::copysign(0.5, x);

        if e == 0xff {

            if (t.wrapping_shl(9)) != 0 {

                return x + x;

            } // nan

            return f; // inf

        }

        // Warning: 0x1.45f306p-2f / x underflows for |x| >= 0x1.45f306p+124

        return if x.abs() >= f32::from_bits(0x7da2f983) {

            f - f32::copysign(f32::from_bits(0x32800000), x)

        } else {

            f - f32::from_bits(0x3ea2f983) / x

        };

    }

    let mut z = x as f64;

    if e < 127 - 13 {

        // |x| < 2^-13

        let sx = z * f64::from_bits(0x3fd45f306dc9c883);

        if e < 127 - 25 {

            // |x| < 2^-25

            return sx as f32;

        }

        let zz0 = sx - (f64::from_bits(0x3fd5555555555555) * sx) * (x as f64 * x as f64);

        return zz0 as f32;

    }

    let ax = t & 0x7fff_ffff;

    if ax == 0x3fa267ddu32 {

        return f32::copysign(f32::from_bits(0x3e933802), x)

            - f32::copysign(f32::from_bits(0x24000000), x);

    };

    if ax == 0x3f693531u32 {

        return f32::copysign(f32::from_bits(0x3e70d331), x)

            + f32::copysign(f32::from_bits(0x31800000), x);

    };

    if ax == 0x3f800000u32 {

        return f32::copysign(f32::from_bits(0x3e800000), x);

    };

    if gt {

        z = 1. / z;

    }

    let z2 = z * z;

    let z4 = z2 * z2;

    let z8 = z4 * z4;

    const CN: [u64; 6] = [

        0x3fd45f306dc9c882,

        0x3fe733b561bc23d5,

        0x3fe28d9805bdfbf2,

        0x3fc8c3ba966ae287,

        0x3f994a7f81ee634b,

        0x3f4a6bbf6127a6df,

    ];

    let mut cn0 = fma(z2, f64::from_bits(CN[1]), f64::from_bits(CN[0]));

    let cn2 = fma(z2, f64::from_bits(CN[3]), f64::from_bits(CN[2]));

    let cn4 = fma(z2, f64::from_bits(CN[5]), f64::from_bits(CN[4]));

    cn0 += z4 * cn2;

    cn0 += z8 * cn4;

    cn0 *= z;

    const CD: [u64; 7] = [

        0x3ff0000000000000,

        0x4004e3b3ecc2518f,

        0x4003ef4a360ff063,

        0x3ff0f1dc55bad551,

        0x3fc8da0fecc018a4,

        0x3f88fa87803776bf,

        0x3f1dadf2ca0acb43,

    ];

    let mut cd0 = fma(z2, f64::from_bits(CD[1]), f64::from_bits(CD[0]));

    let cd2 = fma(z2, f64::from_bits(CD[3]), f64::from_bits(CD[2]));

    let mut cd4 = fma(z2, f64::from_bits(CD[5]), f64::from_bits(CD[4]));

    let cd6 = f64::from_bits(CD[6]);

    cd0 += z4 * cd2;

    cd4 += z4 * cd6;

    cd0 = fma(z8, cd4, cd0);

    let mut r = cn0 / cd0;

    if gt {

        r = f64::copysign(0.5, z) - r;

    }

    r as f32

}

Unexecuted instantiation: pxfm::tangent::atanpif::atanpif_gen_impl::<<f64>::mul_add>

Unexecuted instantiation: pxfm::tangent::atanpif::atanpif_gen_impl::<pxfm::common::f_fmla>

#[cfg(any(target_arch = "x86", target_arch = "x86_64"))]

#[target_feature(enable = "avx", enable = "fma")]

unsafe fn atanpif_fma_impl(x: f32) -> f32 {

    atanpif_gen_impl(x, f64::mul_add)

}

/// Computes atan(x)/PI

///

/// Max ULP 0.5

#[inline]

pub fn f_atanpif(x: f32) -> f32 {

    #[cfg(not(any(target_arch = "x86", target_arch = "x86_64")))]

    {

        atanpif_gen_impl(x, f_fmla)

    }

    #[cfg(any(target_arch = "x86", target_arch = "x86_64"))]

    {

        use std::sync::OnceLock;

        static EXECUTOR: OnceLock<unsafe fn(f32) -> f32> = OnceLock::new();

        let q = EXECUTOR.get_or_init(|| {

            if std::arch::is_x86_feature_detected!("avx")

                && std::arch::is_x86_feature_detected!("fma")

            {

                atanpif_fma_impl

            } else {

                fn def_atanpif(x: f32) -> f32 {

                    atanpif_gen_impl(x, f_fmla)

                }

                def_atanpif

            }

        });

        unsafe { q(x) }

    }

}

#[cfg(test)]

mod tests {

    use super::*;

    #[test]

    fn test_atanpif() {

        assert_eq!(f_atanpif(0.0), 0.0);

        assert_eq!(f_atanpif(1.0), 0.25);

        assert_eq!(f_atanpif(1.5), 0.31283295);

        assert_eq!(f_atanpif(-1.0), -0.25);

        assert_eq!(f_atanpif(-1.5), -0.31283295);

    }

}