/*

 * // 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;

use crate::logs::LOG_RANGE_REDUCTION;

use crate::polyeval::{f_estrin_polyeval7, f_polyeval6};

// Generated in SageMath:

// print("[")

// for i in range(128):

//     R = RealField(200)

//     r = R(2)**(-8) * ( R(2)**8 * (R(1) - R(2)**(-8)) / (R(1) + R(i)*R(2)**-7) ).ceil()

//

//     if i == 0 or i == 127:

//         print(double_to_hex(0), ",")

//     else:

//         print(double_to_hex(-r.log2()), ",")

// print("];")

static LOG2_D: [u64; 128] = [

    0x0000000000000000,

    0x3f872c7ba20f7327,

    0x3f9743ee861f3556,

    0x3fa184b8e4c56af8,

    0x3fa77394c9d958d5,

    0x3fad6ebd1f1febfe,

    0x3fb1bb32a600549d,

    0x3fb4c560fe68af88,

    0x3fb7d60496cfbb4c,

    0x3fb960caf9abb7ca,

    0x3fbc7b528b70f1c5,

    0x3fbf9c95dc1d1165,

    0x3fc097e38ce60649,

    0x3fc22dadc2ab3497,

    0x3fc3c6fb650cde51,

    0x3fc494f863b8df35,

    0x3fc633a8bf437ce1,

    0x3fc7046031c79f85,

    0x3fc8a8980abfbd32,

    0x3fc97c1cb13c7ec1,

    0x3fcb2602497d5346,

    0x3fcbfc67a7fff4cc,

    0x3fcdac22d3e441d3,

    0x3fce857d3d361368,

    0x3fd01d9bbcfa61d4,

    0x3fd08bce0d95fa38,

    0x3fd169c05363f158,

    0x3fd1d982c9d52708,

    0x3fd249cd2b13cd6c,

    0x3fd32bfee370ee68,

    0x3fd39de8e1559f6f,

    0x3fd4106017c3eca3,

    0x3fd4f6fbb2cec598,

    0x3fd56b22e6b578e5,

    0x3fd5dfdcf1eeae0e,

    0x3fd6552b49986277,

    0x3fd6cb0f6865c8ea,

    0x3fd7b89f02cf2aad,

    0x3fd8304d90c11fd3,

    0x3fd8a8980abfbd32,

    0x3fd921800924dd3b,

    0x3fd99b072a96c6b2,

    0x3fda8ff971810a5e,

    0x3fdb0b67f4f46810,

    0x3fdb877c57b1b070,

    0x3fdc043859e2fdb3,

    0x3fdc819dc2d45fe4,

    0x3fdcffae611ad12b,

    0x3fdd7e6c0abc3579,

    0x3fddfdd89d586e2b,

    0x3fde7df5fe538ab3,

    0x3fdefec61b011f85,

    0x3fdf804ae8d0cd02,

    0x3fe0014332be0033,

    0x3fe042bd4b9a7c99,

    0x3fe08494c66b8ef0,

    0x3fe0c6caaf0c5597,

    0x3fe1096015dee4da,

    0x3fe14c560fe68af9,

    0x3fe18fadb6e2d3c2,

    0x3fe1d368296b5255,

    0x3fe217868b0c37e8,

    0x3fe25c0a0463beb0,

    0x3fe2a0f3c340705c,

    0x3fe2e644fac04fd8,

    0x3fe2e644fac04fd8,

    0x3fe32bfee370ee68,

    0x3fe37222bb70747c,

    0x3fe3b8b1c68fa6ed,

    0x3fe3ffad4e74f1d6,

    0x3fe44716a2c08262,

    0x3fe44716a2c08262,

    0x3fe48eef19317991,

    0x3fe4d7380dcc422d,

    0x3fe51ff2e30214bc,

    0x3fe5692101d9b4a6,

    0x3fe5b2c3da19723b,

    0x3fe5b2c3da19723b,

    0x3fe5fcdce2727ddb,

    0x3fe6476d98ad990a,

    0x3fe6927781d932a8,

    0x3fe6927781d932a8,

    0x3fe6ddfc2a78fc63,

    0x3fe729fd26b707c8,

    0x3fe7767c12967a45,

    0x3fe7767c12967a45,

    0x3fe7c37a9227e7fb,

    0x3fe810fa51bf65fd,

    0x3fe810fa51bf65fd,

    0x3fe85efd062c656d,

    0x3fe8ad846cf369a4,

    0x3fe8ad846cf369a4,

    0x3fe8fc924c89ac84,

    0x3fe94c287492c4db,

    0x3fe94c287492c4db,

    0x3fe99c48be2063c8,

    0x3fe9ecf50bf43f13,

    0x3fe9ecf50bf43f13,

    0x3fea3e2f4ac43f60,

    0x3fea8ff971810a5e,

    0x3fea8ff971810a5e,

    0x3feae255819f022d,

    0x3feb35458761d479,

    0x3feb35458761d479,

    0x3feb88cb9a2ab521,

    0x3feb88cb9a2ab521,

    0x3febdce9dcc96187,

    0x3fec31a27dd00b4a,

    0x3fec31a27dd00b4a,

    0x3fec86f7b7ea4a89,

    0x3fec86f7b7ea4a89,

    0x3fecdcebd2373995,

    0x3fed338120a6dd9d,

    0x3fed338120a6dd9d,

    0x3fed8aba045b01c8,

    0x3fed8aba045b01c8,

    0x3fede298ec0bac0d,

    0x3fede298ec0bac0d,

    0x3fee3b20546f554a,

    0x3fee3b20546f554a,

    0x3fee9452c8a71028,

    0x3fee9452c8a71028,

    0x3feeee32e2aeccbf,

    0x3feeee32e2aeccbf,

    0x3fef48c34bd1e96f,

    0x3fef48c34bd1e96f,

    0x3fefa406bd2443df,

    0x0000000000000000,

];

#[inline]

pub(crate) fn core_log2f(x: f64) -> f64 {

    let x_u = x.to_bits();

    const E_BIAS: u64 = (1u64 << (11 - 1u64)) - 1u64;

    let mut x_e: i32 = -(E_BIAS as i32);

    // log2(x) = log2(2^x_e * x_m)

    //         = x_e + log2(x_m)

    // Range reduction for log2(x_m):

    // For each x_m, we would like to find r such that:

    //   -2^-8 <= r * x_m - 1 < 2^-7

    let shifted = (x_u >> 45) as i32;

    let index = shifted & 0x7F;

    let r = f64::from_bits(LOG_RANGE_REDUCTION[index as usize]);

    // Add unbiased exponent. Add an extra 1 if the 8 leading fractional bits are

    // all 1's.

    x_e = x_e.wrapping_add(x_u.wrapping_add(1u64 << 45).wrapping_shr(52) as i32);

    let e_x = x_e as f64;

    let log_r_dd = LOG2_D[index as usize];

    // hi is exact

    let hi = e_x + f64::from_bits(log_r_dd);

    // Set m = 1.mantissa.

    let x_m = (x_u & 0x000F_FFFF_FFFF_FFFFu64) | 0x3FF0_0000_0000_0000u64;

    let m = f64::from_bits(x_m);

    let u;

    #[cfg(any(

        all(

            any(target_arch = "x86", target_arch = "x86_64"),

            target_feature = "fma"

        ),

        target_arch = "aarch64"

    ))]

    {

        u = f_fmla(r, m, -1.0); // exact

    }

    #[cfg(not(any(

        all(

            any(target_arch = "x86", target_arch = "x86_64"),

            target_feature = "fma"

        ),

        target_arch = "aarch64"

    )))]

    {

        use crate::logs::LOG_CD;

        let c_m = x_m & 0x3FFF_E000_0000_0000u64;

        let c = f64::from_bits(c_m);

        u = f_fmla(r, m - c, f64::from_bits(LOG_CD[index as usize])); // exact

    }

    // Polynomial for log(1+x)/x generated in Sollya:

    // d = [-2^-8, 2^-7];

    // f_log2p1 = log2(1 + x)/x;

    // Q = fpminimax(f_log2p1, 6, [|D...|], d);

    // See ./notes/log10pf_core.sollya

    let p = f_polyeval6(

        u,

        f64::from_bits(0x3ff71547652b82fe),

        f64::from_bits(0xbfe71547652b82e7),

        f64::from_bits(0x3fdec709dc3b1fd5),

        f64::from_bits(0xbfd7154766124214),

        f64::from_bits(0x3fd2776bd902599e),

        f64::from_bits(0xbfcec586c6f55d08),

    );

    f_fmla(p, u, hi)

}

/// Computes log2(x+1)

///

/// Max ULP 0.5

#[inline]

pub fn f_log2p1f(x: f32) -> f32 {

    let z = x as f64;

    let ux = x.to_bits().wrapping_shl(1);

    if ux >= 0xffu32 << 24 || ux == 0 {

        // |x| == 0, |x| == inf, x == NaN

        if ux == 0 {

            return x;

        }

        if x.is_infinite() {

            return if x.is_sign_positive() {

                f32::INFINITY

            } else {

                f32::NAN

            };

        }

        return x + f32::NAN;

    }

    let ax = x.to_bits() & 0x7fff_ffffu32;

    // Use log2p1(x) = log10(1 + x) for |x| > 2^-6;

    if ax > 0x3c80_0000u32 {

        if x == -1. {

            return f32::NEG_INFINITY;

        }

        let x1p = z + 1.;

        if x1p <= 0. {

            if x1p == 0. {

                return f32::NEG_INFINITY;

            }

            return f32::NAN;

        }

        return core_log2f(x1p) as f32;

    }

    // log2p1 is expected to be used near zero:

    // Polynomial generated by Sollya:

    // d = [-2^-6; 2^-6];

    // f_log2pf = log2(1+x)/x;

    // Q = fpminimax(f_log2pf, 6, [|D...|], d);

    const C: [u64; 7] = [

        0x3ff71547652b82fe,

        0xbfe71547652b8d18,

        0x3fdec709dc3a501c,

        0xbfd715475b117c95,

        0x3fd2776c3fd833bd,

        0xbfcec9905627faa6,

        0x3fca64536a0ad148,

    ];

    let p = f_estrin_polyeval7(

        z,

        f64::from_bits(C[0]),

        f64::from_bits(C[1]),

        f64::from_bits(C[2]),

        f64::from_bits(C[3]),

        f64::from_bits(C[4]),

        f64::from_bits(C[5]),

        f64::from_bits(C[6]),

    );

    (p * z) as f32

}

#[cfg(test)]

mod tests {

    use super::*;

    #[test]

    fn test_log2p1f() {

        assert_eq!(f_log2p1f(0.0), 0.0);

        assert_eq!(f_log2p1f(1.0), 1.0);

        assert_eq!(f_log2p1f(-0.0432432), -0.063775845);

        assert_eq!(f_log2p1f(-0.009874634), -0.01431689);

        assert_eq!(f_log2p1f(1.2443), 1.1662655);

        assert_eq!(f_log2p1f(f32::INFINITY), f32::INFINITY);

        assert!(f_log2p1f(f32::NEG_INFINITY).is_nan());

        assert!(f_log2p1f(-1.0432432).is_nan());

    }

}