/*

 * // 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::acosf::poly12;

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

#[cold]

fn as_special(x: f32) -> f32 {

    let t = x.to_bits();

    let ax = t.wrapping_shl(1);

    if ax > (0xffu32 << 24) {

        return x + x;

    } // nan

    f32::NAN

}

/// Computes asin

///

/// Max found ULP 0.49999928

#[inline]

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

    const PI2: f64 = f64::from_bits(0x3ff921fb54442d18);

    let xs = x as f64;

    let mut r;

    let t = x.to_bits();

    let ax = t.wrapping_shl(1);

    if ax > 0x7f << 24 {

        return as_special(x);

    }

    if ax < 0x7ec29000u32 {

        // |x| < 1.49029

        if ax < 115 << 24 {

            // |x| < 0.000244141

            return dd_fmlaf(x, f64::from_bits(0x3e60000000000000) as f32, x);

        }

        const B: [u64; 16] = [

            0x3ff0000000000005,

            0x3fc55557aeca105d,

            0x3fb3314ec3db7d12,

            0x3fa775738a5a6f92,

            0x3f75d5f7ce1c8538,

            0x3fd605c6d58740f0,

            0xc005728b732d73c6,

            0x402f152170f151eb,

            0xc04f962ea3ca992e,

            0x40671971e17375a0,

            0xc07860512b4ba230,

            0x40826a3b8d4bdb14,

            0xc0836f2ea5698b51,

            0x407b3d722aebfa2e,

            0xc066cf89703b1289,

            0x4041518af6a65e2d,

        ];

        let z = xs;

        let z2 = z * z;

        let w0 = f_fmla(z2, f64::from_bits(B[1]), f64::from_bits(B[0]));

        let w1 = f_fmla(z2, f64::from_bits(B[3]), f64::from_bits(B[2]));

        let w2 = f_fmla(z2, f64::from_bits(B[5]), f64::from_bits(B[4]));

        let w3 = f_fmla(z2, f64::from_bits(B[7]), f64::from_bits(B[6]));

        let w4 = f_fmla(z2, f64::from_bits(B[9]), f64::from_bits(B[8]));

        let w5 = f_fmla(z2, f64::from_bits(B[11]), f64::from_bits(B[10]));

        let w6 = f_fmla(z2, f64::from_bits(B[13]), f64::from_bits(B[12]));

        let w7 = f_fmla(z2, f64::from_bits(B[15]), f64::from_bits(B[14]));

        let z4 = z2 * z2;

        let z8 = z4 * z4;

        let z16 = z8 * z8;

        r = z

            * ((f_fmla(z4, w1, w0) + z8 * f_fmla(z4, w3, w2))

                + z16 * (f_fmla(z4, w5, w4) + z8 * f_fmla(z4, w7, w6)));

        let ub = r;

        let lb = r - z * f64::from_bits(0x3e0efa8eb0000000);

        // Ziv's accuracy test

        if ub == lb {

            return ub as f32;

        }

    }

    if ax < (0x7eu32 << 24) {

        const C: [u64; 12] = [

            0x3fc555555555529c,

            0x3fb333333337e0dd,

            0x3fa6db6db3b4465e,

            0x3f9f1c72e13ac306,

            0x3f96e89cebe06bc4,

            0x3f91c6dcf5289094,

            0x3f8c6dbbcc7c6315,

            0x3f88f8dc2615e996,

            0x3f7a5833b7bf15e8,

            0x3f943f44ace1665c,

            0xbf90fb17df881c73,

            0x3fa07520c026b2d6,

        ];

        let z = xs;

        let z2 = z * z;

        let c0 = poly12(z2, C);

        r = z + (z * z2) * c0;

    } else {

        if ax == 0x7e55688au32 {

            return f32::copysign(f64::from_bits(0x3fe75b8a20000000) as f32, x)

                + f32::copysign(f64::from_bits(0x3e50000000000000) as f32, x);

        }

        if ax == 0x7e107434u32 {

            return f32::copysign(f64::from_bits(0x3fe1f4b640000000) as f32, x)

                + f32::copysign(f64::from_bits(0x3e50000000000000) as f32, x);

        }

        let bx = xs.abs();

        let z = 1.0 - bx;

        let s = z.sqrt();

        const C: [u64; 12] = [

            0x3ff6a09e667f3bcb,

            0x3fbe2b7dddff2db9,

            0x3f9b27247ab42dbc,

            0x3f802995cc4e0744,

            0x3f65ffb0276ec8ea,

            0x3f5033885a928dec,

            0x3f3911f2be23f8c7,

            0x3f24c3c55d2437fd,

            0x3f0af477e1d7b461,

            0x3f0abd6bdff67dcb,

            0xbef1717e86d0fa28,

            0x3ef6ff526de46023,

        ];

        r = PI2 - s * poly12(z, C);

        r = f64::copysign(r, xs);

    }

    r as f32

}

#[cfg(test)]

mod tests {

    use super::*;

    #[test]

    fn test_asinf() {

        assert_eq!(f_asinf(-0.5), -std::f32::consts::FRAC_PI_6);

        assert_eq!(f_asinf(0.5), std::f32::consts::FRAC_PI_6);

        assert!(f_asinf(7.).is_nan());

    }

}