/*

 * // 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::asinpif::ASINCOSF_PI_TABLE;

use crate::common::{dd_fmla, f_fmla};

#[inline(always)]

/// fma - fma

/// dd_fma - mandatory fma fallback

fn acospif_gen_impl<Q: Fn(f64, f64, f64) -> f64, F: Fn(f64, f64, f64) -> f64>(

    x: f32,

    fma: Q,

    dd_fma: F,

) -> f32 {

    let ax = x.abs();

    let az = ax as f64;

    let z = x as f64;

    let t: u32 = x.to_bits();

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

    if e >= 127 {

        if x == 1.0 {

            return 0.0;

        }

        if x == -1.0 {

            return 1.0;

        }

        if e == 0xff && (t.wrapping_shl(9)) != 0 {

            return x + x;

        } // nan

        return f32::NAN;

    }

    let s: i32 = 146i32.wrapping_sub(e);

    let mut i = 0i32;

    if s < 32 {

        i = (((t & 0x007fffff) | 1 << 23) >> s) as i32;

    }

    let c = ASINCOSF_PI_TABLE[i as usize & 15];

    let z2 = z * z;

    let z4 = z2 * z2;

    if i == 0 {

        let mut c0 = fma(z2, f64::from_bits(c[1]), f64::from_bits(c[0]));

        let c2 = fma(z2, f64::from_bits(c[3]), f64::from_bits(c[2]));

        let mut c4 = fma(z2, f64::from_bits(c[5]), f64::from_bits(c[4]));

        let c6 = fma(z2, f64::from_bits(c[7]), f64::from_bits(c[6]));

        c0 += c2 * z4;

        c4 += c6 * z4;

        /* For |x| <= 0x1.0fd288p-127, c0 += c4*(z4*z4) would raise a spurious

        underflow exception, we use an FMA instead, where c4 * z4 does not

        underflow. */

        c0 = dd_fma(c4 * z4, z4, c0);

        fma(-z, c0, 0.5) as f32

    } else {

        let f = (1. - az).sqrt();

        let mut c0 = fma(az, f64::from_bits(c[1]), f64::from_bits(c[0]));

        let c2 = fma(az, f64::from_bits(c[3]), f64::from_bits(c[2]));

        let mut c4 = fma(az, f64::from_bits(c[5]), f64::from_bits(c[4]));

        let c6 = fma(az, f64::from_bits(c[7]), f64::from_bits(c[6]));

        c0 += c2 * z2;

        c4 += c6 * z2;

        c0 += c4 * z4;

        static SIGN: [f64; 2] = [0., 1.];

        let r = SIGN[(t >> 31) as usize] + c0 * f64::copysign(f, x as f64);

        r as f32

    }

}

Unexecuted instantiation: pxfm::acospif::acospif_gen_impl::<<f64>::mul_add, <f64>::mul_add>

Unexecuted instantiation: pxfm::acospif::acospif_gen_impl::<pxfm::common::f_fmla, pxfm::common::dd_fmla>

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

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

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

    acospif_gen_impl(x, f64::mul_add, f64::mul_add)

}

/// Computes acos(x)/PI

///

/// Max ULP 0.5

#[inline]

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

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

    {

        acospif_gen_impl(x, f_fmla, dd_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")

            {

                acospif_fma_impl

            } else {

                fn def_acospif(x: f32) -> f32 {

                    acospif_gen_impl(x, f_fmla, dd_fmla)

                }

                def_acospif

            }

        });

        unsafe { q(x) }

    }

}

#[cfg(test)]

mod tests {

    use super::*;

    #[test]

    fn test_acospif() {

        assert_eq!(f_acospif(0.0), 0.5);

        assert_eq!(f_acospif(0.5), 0.33333334);

        assert_eq!(f_acospif(1.0), 0.0);

    }

}