/*

 * // 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::bits::get_exponent_f64;

#[allow(unused_imports)]

use crate::common::*;

use std::ops::{Mul, Neg};

// https://hal.science/hal-01351529v3/document

#[derive(Copy, Clone, Default, Debug)]

pub(crate) struct DoubleDouble {

    pub(crate) lo: f64,

    pub(crate) hi: f64,

}

impl Neg for DoubleDouble {

    type Output = Self;

    #[inline]

    fn neg(self) -> Self::Output {

        Self {

            hi: -self.hi,

            lo: -self.lo,

        }

    }

}

impl DoubleDouble {

    #[inline]

    pub(crate) const fn from_bit_pair(pair: (u64, u64)) -> Self {

        Self {

            lo: f64::from_bits(pair.0),

            hi: f64::from_bits(pair.1),

        }

    }

    #[inline]

    pub(crate) const fn new(lo: f64, hi: f64) -> Self {

        DoubleDouble { lo, hi }

    }

Unexecuted instantiation: <pxfm::double_double::DoubleDouble>::new

Unexecuted instantiation: <pxfm::double_double::DoubleDouble>::new

    // Non FMA helper

    #[allow(dead_code)]

    #[inline]

    pub(crate) const fn split(a: f64) -> DoubleDouble {

        // CN = 2^N.

        const CN: f64 = (1 << 27) as f64;

        const C: f64 = CN + 1.0;

        let t1 = C * a;

        let t2 = a - t1;

        let r_hi = t1 + t2;

        let r_lo = a - r_hi;

        DoubleDouble::new(r_lo, r_hi)

    }

Unexecuted instantiation: <pxfm::double_double::DoubleDouble>::split

Unexecuted instantiation: <pxfm::double_double::DoubleDouble>::split

    // Non FMA helper

    #[allow(dead_code)]

    #[inline]

    fn from_exact_mult_impl_non_fma(asz: DoubleDouble, a: f64, b: f64) -> Self {

        let bs = DoubleDouble::split(b);

        let r_hi = a * b;

        let t1 = asz.hi * bs.hi - r_hi;

        let t2 = asz.hi * bs.lo + t1;

        let t3 = asz.lo * bs.hi + t2;

        let r_lo = asz.lo * bs.lo + t3;

        DoubleDouble::new(r_lo, r_hi)

    }

Unexecuted instantiation: <pxfm::double_double::DoubleDouble>::from_exact_mult_impl_non_fma

Unexecuted instantiation: <pxfm::double_double::DoubleDouble>::from_exact_mult_impl_non_fma

    // valid only for |a| > b

    #[inline]

    pub(crate) const fn from_exact_add(a: f64, b: f64) -> DoubleDouble {

        let r_hi = a + b;

        let t = r_hi - a;

        let r_lo = b - t;

        DoubleDouble::new(r_lo, r_hi)

    }

Unexecuted instantiation: <pxfm::double_double::DoubleDouble>::from_exact_add

Unexecuted instantiation: <pxfm::double_double::DoubleDouble>::from_exact_add

    // valid only for |a| > b

    #[inline]

    pub(crate) const fn from_exact_sub(a: f64, b: f64) -> DoubleDouble {

        let r_hi = a - b;

        let t = a - r_hi;

        let r_lo = t - b;

        DoubleDouble::new(r_lo, r_hi)

    }

    #[inline]

    pub(crate) const fn from_full_exact_add(a: f64, b: f64) -> DoubleDouble {

        let r_hi = a + b;

        let t1 = r_hi - a;

        let t2 = r_hi - t1;

        let t3 = b - t1;

        let t4 = a - t2;

        let r_lo = t3 + t4;

        DoubleDouble::new(r_lo, r_hi)

    }

    #[allow(unused)]

    #[inline]

    pub(crate) fn dd_f64_mul_add(a: f64, b: f64, c: f64) -> f64 {

        let ddx2 = DoubleDouble::from_exact_mult(a, b);

        let zv = DoubleDouble::full_add_f64(ddx2, c);

        zv.to_f64()

    }

    #[inline]

    pub(crate) const fn from_full_exact_sub(a: f64, b: f64) -> Self {

        let r_hi = a - b;

        let t1 = r_hi - a;

        let t2 = r_hi - t1;

        let t3 = -b - t1;

        let t4 = a - t2;

        let r_lo = t3 + t4;

        DoubleDouble::new(r_lo, r_hi)

    }

    #[inline]

    pub(crate) fn add(a: DoubleDouble, b: DoubleDouble) -> DoubleDouble {

        let s = a.hi + b.hi;

        let d = s - a.hi;

        let l = ((b.hi - d) + (a.hi + (d - s))) + (a.lo + b.lo);

        DoubleDouble::new(l, s)

    }

    #[inline]

    pub(crate) fn quick_dd_add(a: DoubleDouble, b: DoubleDouble) -> DoubleDouble {

        let DoubleDouble { hi: sh, lo: sl } = DoubleDouble::from_full_exact_add(a.hi, b.hi);

        let v = a.lo + b.lo;

        let w = sl + v;

        DoubleDouble::from_exact_add(sh, w)

    }

    #[inline]

    pub(crate) fn quick_dd_sub(a: DoubleDouble, b: DoubleDouble) -> DoubleDouble {

        let DoubleDouble { hi: sh, lo: sl } = DoubleDouble::from_full_exact_sub(a.hi, b.hi);

        let v = a.lo - b.lo;

        let w = sl + v;

        DoubleDouble::from_exact_add(sh, w)

    }

    #[inline]

    pub(crate) fn full_dd_add(a: DoubleDouble, b: DoubleDouble) -> DoubleDouble {

        let DoubleDouble { hi: sh, lo: sl } = DoubleDouble::from_full_exact_add(a.hi, b.hi);

        let DoubleDouble { hi: th, lo: tl } = DoubleDouble::from_full_exact_add(a.lo, b.lo);

        let c = sl + th;

        let v = DoubleDouble::from_exact_add(sh, c);

        let w = tl + v.lo;

        DoubleDouble::from_exact_add(v.hi, w)

    }

    #[inline]

    pub(crate) fn full_dd_sub(a: DoubleDouble, b: DoubleDouble) -> DoubleDouble {

        DoubleDouble::full_dd_add(a, -b)

    }

    #[inline]

    pub(crate) fn sub(a: DoubleDouble, b: DoubleDouble) -> DoubleDouble {

        let s = a.hi - b.hi;

        let d = s - a.hi;

        let l = ((-b.hi - d) + (a.hi + (d - s))) + (a.lo - b.lo);

        DoubleDouble::new(l, s)

    }

    /// DoubleDouble-style square root for a double-double number

    #[inline]

    pub(crate) fn sqrt(self) -> DoubleDouble {

        let a = self.hi + self.lo;

        if a == 0.0 {

            return DoubleDouble { hi: 0.0, lo: 0.0 };

        }

        if a < 0.0 || a.is_nan() {

            return DoubleDouble {

                hi: f64::NAN,

                lo: 0.0,

            };

        }

        if a.is_infinite() {

            return DoubleDouble {

                hi: f64::INFINITY,

                lo: 0.0,

            };

        }

        let x = a.sqrt();

        let x2 = DoubleDouble::from_exact_mult(x, x);

        // Residual = self - x²

        let mut r = self.hi - x2.hi;

        r += self.lo;

        r -= x2.lo;

        let dx = r / (2.0 * x);

        let hi = x + dx;

        let lo = (x - hi) + dx;

        DoubleDouble { hi, lo }

    }

    /// DoubleDouble-style square root for a double-double number

    #[inline]

    pub(crate) fn fast_sqrt(self) -> DoubleDouble {

        let a = self.hi + self.lo;

        let x = a.sqrt();

        let x2 = DoubleDouble::from_exact_mult(x, x);

        // Residual = self - x²

        let mut r = self.hi - x2.hi;

        r += self.lo;

        r -= x2.lo;

        let dx = r / (2.0 * x);

        let hi = x + dx;

        let lo = (x - hi) + dx;

        DoubleDouble { hi, lo }

    }

    /// `a*b+c`

    ///

    /// *Accurate dot product (Ogita, Rump and Oishi 2004)*

    #[inline]

    pub(crate) fn mul_add_f64(a: DoubleDouble, b: DoubleDouble, c: f64) -> DoubleDouble {

        let DoubleDouble { hi: h, lo: r } = DoubleDouble::quick_mult(a, b);

        let DoubleDouble { hi: p, lo: q } = DoubleDouble::from_full_exact_add(c, h);

        DoubleDouble::new(r + q, p)

    }

    /// `a*b+c`

    ///

    /// *Accurate dot product (Ogita, Rump and Oishi 2004)*

    #[inline(always)]

    #[allow(unused)]

    pub(crate) fn mul_add_f64_fma(a: DoubleDouble, b: DoubleDouble, c: f64) -> DoubleDouble {

        let DoubleDouble { hi: h, lo: r } = DoubleDouble::quick_mult_fma(a, b);

        let DoubleDouble { hi: p, lo: q } = DoubleDouble::from_full_exact_add(c, h);

        DoubleDouble::new(r + q, p)

    }

    /// `a*b+c`

    ///

    /// *Accurate dot product (Ogita, Rump and Oishi 2004)*

    #[inline]

    pub(crate) fn quick_mul_add_f64(a: DoubleDouble, b: DoubleDouble, c: f64) -> DoubleDouble {

        let DoubleDouble { hi: h, lo: r } = DoubleDouble::quick_mult(a, b);

        let DoubleDouble { hi: p, lo: q } = DoubleDouble::from_exact_add(c, h);

        DoubleDouble::new(r + q, p)

    }

    /// `a*b+c`

    ///

    /// *Accurate dot product (Ogita, Rump and Oishi 2004)*

    #[inline]

    pub(crate) fn mul_f64_add_f64(a: DoubleDouble, b: f64, c: f64) -> DoubleDouble {

        let DoubleDouble { hi: h, lo: r } = DoubleDouble::quick_mult_f64(a, b);

        let DoubleDouble { hi: p, lo: q } = DoubleDouble::from_full_exact_add(c, h);

        DoubleDouble::new(r + q, p)

    }

    // /// Accurate reciprocal: 1 / self

    // #[inline]

    // pub(crate) fn recip_raphson(self) -> DoubleDouble {

    //     let y0 = DoubleDouble::recip(self);

    //     let z = DoubleDouble::mul_add_f64(-self, y0, 1.0);

    //     DoubleDouble::mul_add(y0, z, y0)

    // }

    /// Accurate reciprocal: 1 / self

    #[inline]

    pub(crate) fn recip(self) -> DoubleDouble {

        #[cfg(any(

            all(

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

                target_feature = "fma"

            ),

            target_arch = "aarch64"

        ))]

        {

            let y = 1. / self.hi;

            let e1 = f_fmla(-self.hi, y, 1.0);

            let e2 = f_fmla(-self.lo, y, e1);

            let e = y * e2;

            DoubleDouble::new(e, y)

        }

        #[cfg(not(any(

            all(

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

                target_feature = "fma"

            ),

            target_arch = "aarch64"

        )))]

        {

            let y = 1.0 / self.hi;

            let DoubleDouble { hi: p1, lo: err1 } = DoubleDouble::from_exact_mult(self.hi, y);

            let e1 = (1.0 - p1) - err1;

            let DoubleDouble { hi: p2, lo: err2 } = DoubleDouble::from_exact_mult(self.lo, y);

            let e2 = (e1 - p2) - err2;

            let e = y * e2;

            DoubleDouble::new(e, y)

        }

    }

    #[inline]

    pub(crate) fn from_recip(b: f64) -> Self {

        #[cfg(any(

            all(

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

                target_feature = "fma"

            ),

            target_arch = "aarch64"

        ))]

        {

            let x_hi = 1.0 / b;

            let err = f_fmla(-x_hi, b, 1.0);

            let x_lo = err / b;

            Self::new(x_lo, x_hi)

        }

        #[cfg(not(any(

            all(

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

                target_feature = "fma"

            ),

            target_arch = "aarch64"

        )))]

        {

            let x_hi = 1.0 / b;

            let prod = Self::from_exact_mult(x_hi, b);

            let err = (1.0 - prod.hi) - prod.lo;

            let x_lo = err / b;

            Self::new(x_lo, x_hi)

        }

    }

    #[inline(always)]

    #[allow(unused)]

    pub(crate) fn from_quick_recip_fma(b: f64) -> Self {

        let h = 1.0 / b;

        let hl = f64::mul_add(h, -b, 1.) * h;

        DoubleDouble::new(hl, h)

    }

    #[inline]

    pub(crate) fn from_quick_recip(b: f64) -> Self {

        #[cfg(any(

            all(

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

                target_feature = "fma"

            ),

            target_arch = "aarch64"

        ))]

        {

            let h = 1.0 / b;

            let hl = f_fmla(h, -b, 1.) * h;

            DoubleDouble::new(hl, h)

        }

        #[cfg(not(any(

            all(

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

                target_feature = "fma"

            ),

            target_arch = "aarch64"

        )))]

        {

            let h = 1.0 / b;

            let pr = DoubleDouble::from_exact_mult(h, b);

            let err = (1.0 - pr.hi) - pr.lo;

            let hl = err * h;

            DoubleDouble::new(hl, h)

        }

    }

    #[inline]

    pub(crate) fn from_exact_div(a: f64, b: f64) -> Self {

        #[cfg(any(

            all(

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

                target_feature = "fma"

            ),

            target_arch = "aarch64"

        ))]

        {

            let q_hi = a / b;

            let r = f_fmla(-q_hi, b, a);

            let q_lo = r / b;

            Self::new(q_lo, q_hi)

        }

        #[cfg(not(any(

            all(

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

                target_feature = "fma"

            ),

            target_arch = "aarch64"

        )))]

        {

            let q_hi = a / b;

            let p = DoubleDouble::from_exact_mult(q_hi, b);

            let r = DoubleDouble::from_exact_sub(a, p.hi);

            let r = r.hi + (r.lo - p.lo);

            let q_lo = r / b;

            Self::new(q_lo, q_hi)

        }

    }

    // Resistant to overflow without FMA

    #[inline]

    pub(crate) fn from_exact_div_fma(a: f64, b: f64) -> Self {

        let q_hi = a / b;

        let r = f64::mul_add(-q_hi, b, a);

        let q_lo = r / b;

        Self::new(q_lo, q_hi)

    }

    #[inline]

    pub(crate) fn from_sqrt(x: f64) -> Self {

        #[cfg(any(

            all(

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

                target_feature = "fma"

            ),

            target_arch = "aarch64"

        ))]

        {

            let h = x.sqrt();

            /* h = sqrt(x) * (1 + e1) with |e1| < 2^-52

            thus h^2 = x * (1 + e2) with |e2| < 2^-50.999 */

            let e = -f_fmla(h, h, -x); // exact

            /* e = x - h^2 */

            let l = e / (h + h);

            DoubleDouble::new(l, h)

        }

        #[cfg(not(any(

            all(

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

                target_feature = "fma"

            ),

            target_arch = "aarch64"

        )))]

        {

            let h = x.sqrt();

            let prod_hh = DoubleDouble::from_exact_mult(h, h);

            let e = (x - prod_hh.hi) - prod_hh.lo; // exact

            /* e = x - h^2 */

            let l = e / (h + h);

            DoubleDouble::new(l, h)

        }

    }

    /// Safe to overflow underflow division using mandatory FMA.

    #[inline]

    #[allow(dead_code)]

    pub(crate) fn div_safe_dd_f64(a: DoubleDouble, b: f64) -> Self {

        let q1 = a.hi / b;

        let r = f64::mul_add(-q1, b, a.hi);

        let r = r + a.lo;

        let q2 = r / b;

        DoubleDouble::new(q2, q1)

    }

    #[inline]

    pub(crate) fn div_dd_f64(a: DoubleDouble, b: f64) -> Self {

        #[cfg(any(

            all(

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

                target_feature = "fma"

            ),

            target_arch = "aarch64"

        ))]

        {

            let q1 = a.hi / b;

            let r = f_fmla(-q1, b, a.hi);

            let r = r + a.lo;

            let q2 = r / b;

            DoubleDouble::new(q2, q1)

        }

        #[cfg(not(any(

            all(

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

                target_feature = "fma"

            ),

            target_arch = "aarch64"

        )))]

        {

            let th = a.hi / b;

            let prod = DoubleDouble::from_exact_mult(th, b);

            let beta_h = a.hi - prod.hi;

            let beta_l = beta_h - prod.lo;

            let beta = beta_l + a.lo;

            let tl = beta / b;

            DoubleDouble::new(tl, th)

        }

    }

    // /// Dekker division with one refinement step

    // #[inline]

    // pub(crate) fn div_dd_f64_newton_raphson(a: DoubleDouble, b: f64) -> Self {

    //     // Initial estimate q = a / b

    //     let q = DoubleDouble::div_dd_f64(a, b);

    //

    //     // One Newton-Raphson refinement step:

    //     // e = a - q * b

    //     let qb = DoubleDouble::quick_mult_f64(q, b);

    //     let e = DoubleDouble::sub(a, qb);

    //     let e_div_b = DoubleDouble::div_dd_f64(e, b);

    //

    //     DoubleDouble::add(q, e_div_b)

    // }

    // /// Dekker division with two Newton-Raphson refinement steps

    // #[inline]

    // pub(crate) fn div_dd_f64_newton_raphson_2(a: Dekker, b: f64) -> Self {

    //     // First estimate: q = a / b (one round of Dekker division)

    //     let q1 = Dekker::div_dd_f64(a, b);

    //

    //     // First refinement: q2 = q1 + (a - q1 * b) / b

    //     let qb1 = Dekker::quick_mult_f64(q1, b);

    //     let e1 = Dekker::sub(a, qb1);

    //     let dq1 = Dekker::div_dd_f64(e1, b);

    //     let q2 = Dekker::add(q1, dq1);

    //

    //     // Second refinement: q3 = q2 + (a - q2 * b) / b

    //     let qb2 = Dekker::quick_mult_f64(q2, b);

    //     let e2 = Dekker::sub(a, qb2);

    //     let dq2 = Dekker::div_dd_f64(e2, b);

    //

    //     Dekker::add(q2, dq2)

    // }

    // #[inline]

    // pub(crate) fn neg(self) -> Self {

    //     Self {

    //         lo: -self.lo, hi: -self.hi,

    //     }

    // }

    #[inline]

    pub(crate) fn from_f64_div_dd(a: f64, b: DoubleDouble) -> Self {

        let q1 = a / b.hi;

        let prod = DoubleDouble::from_exact_mult(q1, b.hi);

        let prod_lo = f_fmla(q1, b.lo, prod.lo);

        let rem = f_fmla(-1.0, prod.hi, a) - prod_lo;

        let q2 = rem / b.hi;

        DoubleDouble::new(q2, q1)

    }

    #[inline(always)]

    #[allow(unused)]

    pub(crate) fn from_f64_div_dd_fma(a: f64, b: DoubleDouble) -> Self {

        let q1 = a / b.hi;

        let prod = DoubleDouble::from_exact_mult_fma(q1, b.hi);

        let prod_lo = f64::mul_add(q1, b.lo, prod.lo);

        let rem = f64::mul_add(-1.0, prod.hi, a) - prod_lo;

        let q2 = rem / b.hi;

        DoubleDouble::new(q2, q1)

    }

    #[inline(always)]

    #[allow(unused)]

    pub(crate) fn div_fma(a: DoubleDouble, b: DoubleDouble) -> DoubleDouble {

        let q = 1.0 / b.hi;

        let r_hi = a.hi * q;

        let e_hi = f64::mul_add(b.hi, -r_hi, a.hi);

        let e_lo = f64::mul_add(b.lo, -r_hi, a.lo);

        let r_lo = q * (e_hi + e_lo);

        DoubleDouble::new(r_lo, r_hi)

    }

    #[inline]

    pub(crate) fn div(a: DoubleDouble, b: DoubleDouble) -> DoubleDouble {

        let q = 1.0 / b.hi;

        let r_hi = a.hi * q;

        #[cfg(any(

            all(

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

                target_feature = "fma"

            ),

            target_arch = "aarch64"

        ))]

        {

            let e_hi = f_fmla(b.hi, -r_hi, a.hi);

            let e_lo = f_fmla(b.lo, -r_hi, a.lo);

            let r_lo = q * (e_hi + e_lo);

            DoubleDouble::new(r_lo, r_hi)

        }

        #[cfg(not(any(

            all(

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

                target_feature = "fma"

            ),

            target_arch = "aarch64"

        )))]

        {

            let b_hi_r_hi = DoubleDouble::from_exact_mult(b.hi, -r_hi);

            let b_lo_r_hi = DoubleDouble::from_exact_mult(b.lo, -r_hi);

            let e_hi = (a.hi + b_hi_r_hi.hi) + b_hi_r_hi.lo;

            let e_lo = (a.lo + b_lo_r_hi.hi) + b_lo_r_hi.lo;

            let r_lo = q * (e_hi + e_lo);

            DoubleDouble::new(r_lo, r_hi)

        }

    }

    #[inline]

    pub(crate) fn from_exact_mult(a: f64, b: f64) -> Self {

        #[cfg(any(

            all(

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

                target_feature = "fma"

            ),

            target_arch = "aarch64"

        ))]

        {

            let r_hi = a * b;

            let r_lo = f_fmla(a, b, -r_hi);

            DoubleDouble::new(r_lo, r_hi)

        }

        #[cfg(not(any(

            all(

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

                target_feature = "fma"

            ),

            target_arch = "aarch64"

        )))]

        {

            let splat = DoubleDouble::split(a);

            DoubleDouble::from_exact_mult_impl_non_fma(splat, a, b)

        }

    }

Unexecuted instantiation: <pxfm::double_double::DoubleDouble>::from_exact_mult

Unexecuted instantiation: <pxfm::double_double::DoubleDouble>::from_exact_mult

    #[inline(always)]

    #[allow(unused)]

    pub(crate) fn from_exact_mult_fma(a: f64, b: f64) -> Self {

        let r_hi = a * b;

        let r_lo = f64::mul_add(a, b, -r_hi);

        DoubleDouble::new(r_lo, r_hi)

    }

    // #[inline]

    // pub(crate) fn add_f64(&self, other: f64) -> DoubleDouble {

    //     let r = DoubleDouble::from_exact_add(self.hi, other);

    //     Dekker::from_exact_add(r.hi, r.lo + self.lo)

    // }

    // #[inline]

    // pub(crate) fn to_triple(self) -> TripleDouble {

    //     TripleDouble::new(0., self.lo, self.hi)

    // }

    /// Computes `a * b + c`

    /// `b` is an `f64`, `a` and `c` are `DoubleDouble`.

    ///

    /// *Accurate dot product (Ogita, Rump and Oishi 2004)*

    #[inline]

    pub(crate) fn mul_f64_add(a: DoubleDouble, b: f64, c: DoubleDouble) -> Self {

        let DoubleDouble { hi: h, lo: r } = DoubleDouble::quick_mult_f64(a, b);

        let DoubleDouble { hi: p, lo: q } = DoubleDouble::full_add_f64(c, h);

        DoubleDouble::new(r + q, p)

    }

    /// Computes `a * b + c`

    /// `b` is an `f64`, `a` and `c` are `DoubleDouble`.

    ///

    /// *Accurate dot product (Ogita, Rump and Oishi 2004)*

    ///

    /// *Correctness*

    /// |c.hi| > |a.hi * b.hi|

    #[inline]

    pub(crate) fn quick_mul_f64_add(a: DoubleDouble, b: f64, c: DoubleDouble) -> Self {

        let DoubleDouble { hi: h, lo: r } = DoubleDouble::quick_mult_f64(a, b);

        let DoubleDouble { hi: p, lo: q } = DoubleDouble::add_f64(c, h);

        DoubleDouble::new(r + q, p)

    }

    /// Computes `a * b + c`

    ///

    /// *Accurate dot product (Ogita, Rump and Oishi 2004)*

    ///

    /// *Correctness*

    /// |c.hi| > |a.hi * b.hi|

    #[inline]

    pub(crate) fn quick_mul_f64_add_f64(a: DoubleDouble, b: f64, c: f64) -> Self {

        let DoubleDouble { hi: h, lo: r } = DoubleDouble::quick_mult_f64(a, b);

        let DoubleDouble { hi: p, lo: q } = DoubleDouble::from_exact_add(c, h);

        DoubleDouble::new(r + q, p)

    }

    // #[inline]

    // pub(crate) fn mul_f64_add_full(a: DoubleDouble, b: f64, c: DoubleDouble) -> Self {

    //     /*

    //         double _t1, _t2, _t3, _t4, _t5, _t6, _t7, _t8;   \

    //                                                  \

    //         Mul12(&_t1,&_t2,(a),(bh));                       \

    //         Add12(_t3,_t4,(ch),_t1);                         \

    //         _t5 = (bl) * (a);                                \

    //         _t6 = (cl) + _t2;                                \

    //         _t7 = _t5 + _t6;                                 \

    //         _t8 = _t7 + _t4;                                 \

    //         Add12((*(resh)),(*(resl)),_t3,_t8);              \

    //     */

    //     let DoubleDouble { hi: t1, lo: t2 } = DoubleDouble::from_exact_mult(a.hi, b);

    //     let DoubleDouble { hi: t3, lo: t4 } = DoubleDouble::from_full_exact_add(c.hi, t1);

    //     let t5 = a.lo * b;

    //     let t6 = c.lo + t2;

    //     let t7 = t5 + t6;

    //     let t8 = t7 + t4;

    //     DoubleDouble::from_full_exact_add(t3, t8)

    // }

    /// Computes `a * b + c`

    /// `b` is an `f64`, `a` and `c` are `DoubleDouble`.

    ///

    /// *Accurate dot product (Ogita, Rump and Oishi 2004)*

    #[inline]

    pub(crate) fn f64_mul_f64_add(a: f64, b: f64, c: DoubleDouble) -> Self {

        let DoubleDouble { hi: h, lo: r } = DoubleDouble::from_exact_mult(a, b);

        let DoubleDouble { hi: p, lo: q } = DoubleDouble::full_add_f64(c, h);

        DoubleDouble::new(r + q, p)

    }

    // /// Computes `a * b + c`

    // /// `b` is an `f64`, `a` and `c` are `DoubleDouble`.

    // ///

    // /// *Accurate dot product (Ogita, Rump and Oishi 2004)*

    // #[inline]

    // pub(crate) fn single_mul_add(a: f64, b: f64, c: f64) -> Self {

    //     let DoubleDouble { hi: h, lo: r } = DoubleDouble::from_exact_mult(a, b);

    //     let DoubleDouble { hi: p, lo: q } = DoubleDouble::from_full_exact_add(c, h);

    //     DoubleDouble::new(r + q, p)

    // }

    // /// Computes `a * b + c` safe to overflow without FMA

    // /// `b` is an `f64`, `a` and `c` are `DoubleDouble`.

    // ///

    // /// *Accurate dot product (Ogita, Rump and Oishi 2004)*

    // #[inline]

    // pub(crate) fn mul_f64_safe_add(a: DoubleDouble, b: f64, c: DoubleDouble) -> Self {

    //     let DoubleDouble { hi: h, lo: r } = DoubleDouble::quick_mult_safe_f64(a, b);

    //     let DoubleDouble { hi: p, lo: q } = DoubleDouble::full_add_f64(c, h);

    //     DoubleDouble::new(r + q, p)

    // }

    /// `a*b+c`

    ///

    /// *Accurate dot product (Ogita, Rump and Oishi 2004)*

    #[inline]

    pub(crate) fn mul_add(a: DoubleDouble, b: DoubleDouble, c: DoubleDouble) -> Self {

        let DoubleDouble { hi: h, lo: r } = DoubleDouble::quick_mult(a, b);

        let DoubleDouble { hi: p, lo: q } = DoubleDouble::full_add_f64(c, h);

        DoubleDouble::new(r + q, p)

    }

    /// `a*b+c`

    ///

    /// *Accurate dot product (Ogita, Rump and Oishi 2004)*

    #[inline(always)]

    #[allow(unused)]

    pub(crate) fn mul_add_fma(a: DoubleDouble, b: DoubleDouble, c: DoubleDouble) -> Self {

        let DoubleDouble { hi: h, lo: r } = DoubleDouble::quick_mult_fma(a, b);

        let DoubleDouble { hi: p, lo: q } = DoubleDouble::full_add_f64(c, h);

        DoubleDouble::new(r + q, p)

    }

    /// `a*b+c`

    ///

    /// *Accurate dot product (Ogita, Rump and Oishi 2004)*

    ///

    /// *Correctness*

    /// |c.hi| > |a.hi * b.hi|

    #[inline]

    pub(crate) fn quick_mul_add(a: DoubleDouble, b: DoubleDouble, c: DoubleDouble) -> Self {

        let DoubleDouble { hi: h, lo: r } = DoubleDouble::quick_mult(a, b);

        let DoubleDouble { hi: p, lo: q } = DoubleDouble::add_f64(c, h);

        DoubleDouble::new(r + q, p)

    }

    /// `a*b+c`

    ///

    /// *Accurate dot product (Ogita, Rump and Oishi 2004)*

    ///

    /// *Correctness*

    /// |c.hi| > |a.hi * b.hi|

    #[inline(always)]

    #[allow(unused)]

    pub(crate) fn quick_mul_add_fma(a: DoubleDouble, b: DoubleDouble, c: DoubleDouble) -> Self {

        let DoubleDouble { hi: h, lo: r } = DoubleDouble::quick_mult_fma(a, b);

        let DoubleDouble { hi: p, lo: q } = DoubleDouble::add_f64(c, h);

        DoubleDouble::new(r + q, p)

    }

    #[inline]

    pub(crate) fn quick_mult(a: DoubleDouble, b: DoubleDouble) -> Self {

        #[cfg(any(

            all(

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

                target_feature = "fma"

            ),

            target_arch = "aarch64"

        ))]

        {

            let mut r = DoubleDouble::from_exact_mult(a.hi, b.hi);

            let t1 = f_fmla(a.hi, b.lo, r.lo);

            let t2 = f_fmla(a.lo, b.hi, t1);

            r.lo = t2;

            r

        }

        #[cfg(not(any(

            all(

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

                target_feature = "fma"

            ),

            target_arch = "aarch64"

        )))]

        {

            let DoubleDouble { hi: ch, lo: cl1 } = DoubleDouble::from_exact_mult(a.hi, b.hi);

            let tl1 = a.hi * b.lo;

            let tl2 = a.lo * b.hi;

            let cl2 = tl1 + tl2;

            let cl3 = cl1 + cl2;

            DoubleDouble::new(cl3, ch)

        }

    }

    #[inline(always)]

    #[allow(unused)]

    pub(crate) fn quick_mult_fma(a: DoubleDouble, b: DoubleDouble) -> Self {

        let mut r = DoubleDouble::from_exact_mult_fma(a.hi, b.hi);

        let t1 = f64::mul_add(a.hi, b.lo, r.lo);

        let t2 = f64::mul_add(a.lo, b.hi, t1);

        r.lo = t2;

        r

    }

    #[inline]

    pub(crate) fn mult(a: DoubleDouble, b: DoubleDouble) -> Self {

        #[cfg(any(

            all(

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

                target_feature = "fma"

            ),

            target_arch = "aarch64"

        ))]

        {

            let DoubleDouble { hi: ch, lo: cl1 } = DoubleDouble::from_exact_mult(a.hi, b.hi);

            let tl0 = a.lo * b.lo;

            let tl1 = f_fmla(a.hi, b.lo, tl0);

            let cl2 = f_fmla(a.lo, b.hi, tl1);

            let cl3 = cl1 + cl2;

            DoubleDouble::from_exact_add(ch, cl3)

        }

        #[cfg(not(any(

            all(

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

                target_feature = "fma"

            ),

            target_arch = "aarch64"

        )))]

        {

            let DoubleDouble { hi: ch, lo: cl1 } = DoubleDouble::from_exact_mult(a.hi, b.hi);

            let tl1 = a.hi * b.lo;

            let tl2 = a.lo * b.hi;

            let cl2 = tl1 + tl2;

            let cl3 = cl1 + cl2;

            DoubleDouble::from_exact_add(ch, cl3)

        }

    }

    #[inline]

    pub(crate) fn mult_f64(a: DoubleDouble, b: f64) -> Self {

        #[cfg(any(

            all(

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

                target_feature = "fma"

            ),

            target_arch = "aarch64"

        ))]

        {

            let DoubleDouble { hi: ch, lo: cl1 } = DoubleDouble::from_exact_mult(a.hi, b);

            let cl3 = f_fmla(a.lo, b, cl1);

            DoubleDouble::from_exact_add(ch, cl3)

        }

        #[cfg(not(any(

            all(

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

                target_feature = "fma"

            ),

            target_arch = "aarch64"

        )))]

        {

            let DoubleDouble { hi: ch, lo: cl1 } = DoubleDouble::from_exact_mult(a.hi, b);

            let cl2 = a.lo * b;

            let t = DoubleDouble::from_exact_add(ch, cl2);

            let tl2 = t.lo + cl1;

            DoubleDouble::from_exact_add(t.hi, tl2)

        }

    }

    #[inline(always)]

    pub(crate) fn quick_f64_mult(a: f64, b: DoubleDouble) -> DoubleDouble {

        DoubleDouble::quick_mult_f64(b, a)

    }

    #[inline]

    pub(crate) fn quick_mult_f64(a: DoubleDouble, b: f64) -> Self {

        #[cfg(any(

            all(

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

                target_feature = "fma"

            ),

            target_arch = "aarch64"

        ))]

        {

            let h = b * a.hi;

            let l = f_fmla(b, a.lo, f_fmla(b, a.hi, -h));

            Self { lo: l, hi: h }

        }

        #[cfg(not(any(

            all(

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

                target_feature = "fma"

            ),

            target_arch = "aarch64"

        )))]

        {

            let DoubleDouble { hi: ch, lo: cl1 } = DoubleDouble::from_exact_mult(a.hi, b);

            let cl2 = a.lo * b;

            let cl3 = cl1 + cl2;

            DoubleDouble::new(cl3, ch)

        }

    }

    #[inline(always)]

    #[allow(unused)]

    pub(crate) fn quick_mult_f64_fma(a: DoubleDouble, b: f64) -> Self {

        let h = b * a.hi;