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    // Translated from C to Rust. The original C code can be found at
    // https://github.com/ulfjack/ryu and carries the following license:
    //
    // Copyright 2018 Ulf Adams
    //
    // The contents of this file may be used under the terms of the Apache License,
    // Version 2.0.
    //
    //    (See accompanying file LICENSE-Apache or copy at
    //     http://www.apache.org/licenses/LICENSE-2.0)
    //
    // Alternatively, the contents of this file may be used under the terms of
    // the Boost Software License, Version 1.0.
    //    (See accompanying file LICENSE-Boost or copy at
    //     https://www.boost.org/LICENSE_1_0.txt)
    //
    // Unless required by applicable law or agreed to in writing, this software
    // is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
    // KIND, either express or implied.

    use core::ptr;

    // Returns (lo, hi).
    #[cfg(not(integer128))]
    #[cfg_attr(feature = "no-panic", inline)]
    pub fn umul128(a: u64, b: u64) -> (u64, u64) {
        let a_lo = a as u32;
        let a_hi = (a >> 32) as u32;
        let b_lo = b as u32;
        let b_hi = (b >> 32) as u32;

        let b00 = a_lo as u64 * b_lo as u64;
        let b01 = a_lo as u64 * b_hi as u64;
        let b10 = a_hi as u64 * b_lo as u64;
        let b11 = a_hi as u64 * b_hi as u64;

        let b00_lo = b00 as u32;
        let b00_hi = (b00 >> 32) as u32;

        let mid1 = b10 + b00_hi as u64;
        let mid1_lo = mid1 as u32;
        let mid1_hi = (mid1 >> 32) as u32;

        let mid2 = b01 + mid1_lo as u64;
        let mid2_lo = mid2 as u32;
        let mid2_hi = (mid2 >> 32) as u32;

        let p_hi = b11 + mid1_hi as u64 + mid2_hi as u64;
        let p_lo = ((mid2_lo as u64) << 32) | b00_lo as u64;

        (p_lo, p_hi)
    }

    #[cfg(not(integer128))]
    #[cfg_attr(feature = "no-panic", inline)]
    pub fn shiftright128(lo: u64, hi: u64, dist: u32) -> u64 {
        // We don't need to handle the case dist >= 64 here (see above).
        debug_assert!(dist > 0);
        debug_assert!(dist < 64);
        (hi << (64 - dist)) | (lo >> dist)
    }

    #[cfg_attr(feature = "no-panic", inline)]
    pub fn div5(x: u64) -> u64 {
        x / 5
    }

    #[cfg_attr(feature = "no-panic", inline)]
    pub fn div10(x: u64) -> u64 {
        x / 10
    }

    #[cfg_attr(feature = "no-panic", inline)]
    pub fn div100(x: u64) -> u64 {
        x / 100
    }

    #[cfg_attr(feature = "no-panic", inline)]
    fn pow5_factor(mut value: u64) -> u32 {
        let mut count = 0u32;
        loop {
            debug_assert!(value != 0);
            let q = div5(value);
            let r = (value as u32).wrapping_sub(5u32.wrapping_mul(q as u32));
            if r != 0 {
                break;
            }
            value = q;
            count += 1;
        }
        count
    }

    // Returns true if value is divisible by 5^p.
    #[cfg_attr(feature = "no-panic", inline)]
    pub fn multiple_of_power_of_5(value: u64, p: u32) -> bool {
        // I tried a case distinction on p, but there was no performance difference.
        pow5_factor(value) >= p
    }

    // Returns true if value is divisible by 2^p.
    #[cfg_attr(feature = "no-panic", inline)]
    pub fn multiple_of_power_of_2(value: u64, p: u32) -> bool {
        debug_assert!(value != 0);
        debug_assert!(p < 64);
        // __builtin_ctzll doesn't appear to be faster here.
        (value & ((1u64 << p) - 1)) == 0
    }

    #[cfg(integer128)]
    #[cfg_attr(feature = "no-panic", inline)]
    pub fn mul_shift_64(m: u64, mul: &(u64, u64), j: u32) -> u64 {
        let b0 = m as u128 * mul.0 as u128;
        let b2 = m as u128 * mul.1 as u128;
        (((b0 >> 64) + b2) >> (j - 64)) as u64
    }

    #[cfg(integer128)]
    #[cfg_attr(feature = "no-panic", inline)]
    pub unsafe fn mul_shift_all_64(
        m: u64,
        mul: &(u64, u64),
        j: u32,
        vp: *mut u64,
        vm: *mut u64,
        mm_shift: u32,
    ) -> u64 {
        ptr::write(vp, mul_shift_64(4 * m + 2, mul, j));
        ptr::write(vm, mul_shift_64(4 * m - 1 - mm_shift as u64, mul, j));
        mul_shift_64(4 * m, mul, j)
    }

    #[cfg(not(integer128))]
    #[cfg_attr(feature = "no-panic", inline)]
    pub unsafe fn mul_shift_all_64(
        mut m: u64,
        mul: &(u64, u64),
        j: u32,
        vp: *mut u64,
        vm: *mut u64,
        mm_shift: u32,
    ) -> u64 {
        m <<= 1;
        // m is maximum 55 bits
        let (lo, tmp) = umul128(m, mul.0);
        let (mut mid, mut hi) = umul128(m, mul.1);
        mid = mid.wrapping_add(tmp);
        hi = hi.wrapping_add((mid < tmp) as u64); // overflow into hi

        let lo2 = lo.wrapping_add(mul.0);
        let mid2 = mid.wrapping_add(mul.1).wrapping_add((lo2 < lo) as u64);
        let hi2 = hi.wrapping_add((mid2 < mid) as u64);
        ptr::write(vp, shiftright128(mid2, hi2, j - 64 - 1));

        if mm_shift == 1 {
            let lo3 = lo.wrapping_sub(mul.0);
            let mid3 = mid.wrapping_sub(mul.1).wrapping_sub((lo3 > lo) as u64);
            let hi3 = hi.wrapping_sub((mid3 > mid) as u64);
            ptr::write(vm, shiftright128(mid3, hi3, j - 64 - 1));
        } else {
            let lo3 = lo + lo;
            let mid3 = mid.wrapping_add(mid).wrapping_add((lo3 < lo) as u64);
            let hi3 = hi.wrapping_add(hi).wrapping_add((mid3 < mid) as u64);
            let lo4 = lo3.wrapping_sub(mul.0);
            let mid4 = mid3.wrapping_sub(mul.1).wrapping_sub((lo4 > lo3) as u64);
            let hi4 = hi3.wrapping_sub((mid4 > mid3) as u64);
            ptr::write(vm, shiftright128(mid4, hi4, j - 64));
        }

        shiftright128(mid, hi, j - 64 - 1)
    }