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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 crate::common::*;
    #[cfg(not(feature = "small"))]
    pub use crate::d2s_full_table::*;
    use crate::d2s_intrinsics::*;
    #[cfg(feature = "small")]
    pub use crate::d2s_small_table::*;
    #[cfg(not(maybe_uninit))]
    use core::mem;
    #[cfg(maybe_uninit)]
    use core::mem::MaybeUninit;

    pub const DOUBLE_MANTISSA_BITS: u32 = 52;
    pub const DOUBLE_EXPONENT_BITS: u32 = 11;
    pub const DOUBLE_BIAS: i32 = 1023;
    pub const DOUBLE_POW5_INV_BITCOUNT: i32 = 125;
    pub const DOUBLE_POW5_BITCOUNT: i32 = 125;

    #[cfg_attr(feature = "no-panic", inline)]
    pub fn decimal_length17(v: u64) -> u32 {
        // This is slightly faster than a loop.
        // The average output length is 16.38 digits, so we check high-to-low.
        // Function precondition: v is not an 18, 19, or 20-digit number.
        // (17 digits are sufficient for round-tripping.)
        debug_assert!(v < 100000000000000000);

        if v >= 10000000000000000 {
            17
        } else if v >= 1000000000000000 {
            16
        } else if v >= 100000000000000 {
            15
        } else if v >= 10000000000000 {
            14
        } else if v >= 1000000000000 {
            13
        } else if v >= 100000000000 {
            12
        } else if v >= 10000000000 {
            11
        } else if v >= 1000000000 {
            10
        } else if v >= 100000000 {
            9
        } else if v >= 10000000 {
            8
        } else if v >= 1000000 {
            7
        } else if v >= 100000 {
            6
        } else if v >= 10000 {
            5
        } else if v >= 1000 {
            4
        } else if v >= 100 {
            3
        } else if v >= 10 {
            2
        } else {
            1
        }
    }

    // A floating decimal representing m * 10^e.
    pub struct FloatingDecimal64 {
        pub mantissa: u64,
        // Decimal exponent's range is -324 to 308
        // inclusive, and can fit in i16 if needed.
        pub exponent: i32,
    }

    #[cfg_attr(feature = "no-panic", inline)]
    pub fn d2d(ieee_mantissa: u64, ieee_exponent: u32) -> FloatingDecimal64 {
        let (e2, m2) = if ieee_exponent == 0 {
            (
                // We subtract 2 so that the bounds computation has 2 additional bits.
                1 - DOUBLE_BIAS - DOUBLE_MANTISSA_BITS as i32 - 2,
                ieee_mantissa,
            )
        } else {
            (
                ieee_exponent as i32 - DOUBLE_BIAS - DOUBLE_MANTISSA_BITS as i32 - 2,
                (1u64 << DOUBLE_MANTISSA_BITS) | ieee_mantissa,
            )
        };
        let even = (m2 & 1) == 0;
        let accept_bounds = even;

        // Step 2: Determine the interval of valid decimal representations.
        let mv = 4 * m2;
        // Implicit bool -> int conversion. True is 1, false is 0.
        let mm_shift = (ieee_mantissa != 0 || ieee_exponent <= 1) as u32;
        // We would compute mp and mm like this:
        // uint64_t mp = 4 * m2 + 2;
        // uint64_t mm = mv - 1 - mm_shift;

        // Step 3: Convert to a decimal power base using 128-bit arithmetic.
        let mut vr: u64;
        let mut vp: u64;
        let mut vm: u64;
        #[cfg(not(maybe_uninit))]
        {
            vp = unsafe { mem::uninitialized() };
            vm = unsafe { mem::uninitialized() };
        }
        #[cfg(maybe_uninit)]
        let mut vp_uninit: MaybeUninit<u64> = MaybeUninit::uninit();
        #[cfg(maybe_uninit)]
        let mut vm_uninit: MaybeUninit<u64> = MaybeUninit::uninit();
        let e10: i32;
        let mut vm_is_trailing_zeros = false;
        let mut vr_is_trailing_zeros = false;
        if e2 >= 0 {
            // I tried special-casing q == 0, but there was no effect on performance.
            // This expression is slightly faster than max(0, log10_pow2(e2) - 1).
            let q = log10_pow2(e2) - (e2 > 3) as u32;
            e10 = q as i32;
            let k = DOUBLE_POW5_INV_BITCOUNT + pow5bits(q as i32) - 1;
            let i = -e2 + q as i32 + k;
            vr = unsafe {
                mul_shift_all_64(
                    m2,
                    #[cfg(feature = "small")]
                    &compute_inv_pow5(q),
                    #[cfg(not(feature = "small"))]
                    {
                        debug_assert!(q < DOUBLE_POW5_INV_SPLIT.len() as u32);
                        DOUBLE_POW5_INV_SPLIT.get_unchecked(q as usize)
                    },
                    i as u32,
                    #[cfg(maybe_uninit)]
                    {
                        vp_uninit.as_mut_ptr()
                    },
                    #[cfg(not(maybe_uninit))]
                    {
                        &mut vp
                    },
                    #[cfg(maybe_uninit)]
                    {
                        vm_uninit.as_mut_ptr()
                    },
                    #[cfg(not(maybe_uninit))]
                    {
                        &mut vm
                    },
                    mm_shift,
                )
            };
            #[cfg(maybe_uninit)]
            {
                vp = unsafe { vp_uninit.assume_init() };
                vm = unsafe { vm_uninit.assume_init() };
            }
            if q <= 21 {
                // This should use q <= 22, but I think 21 is also safe. Smaller values
                // may still be safe, but it's more difficult to reason about them.
                // Only one of mp, mv, and mm can be a multiple of 5, if any.
                let mv_mod5 = (mv as u32).wrapping_sub(5u32.wrapping_mul(div5(mv) as u32));
                if mv_mod5 == 0 {
                    vr_is_trailing_zeros = multiple_of_power_of_5(mv, q);
                } else if accept_bounds {
                    // Same as min(e2 + (~mm & 1), pow5_factor(mm)) >= q
                    // <=> e2 + (~mm & 1) >= q && pow5_factor(mm) >= q
                    // <=> true && pow5_factor(mm) >= q, since e2 >= q.
                    vm_is_trailing_zeros = multiple_of_power_of_5(mv - 1 - mm_shift as u64, q);
                } else {
                    // Same as min(e2 + 1, pow5_factor(mp)) >= q.
                    vp -= multiple_of_power_of_5(mv + 2, q) as u64;
                }
            }
        } else {
            // This expression is slightly faster than max(0, log10_pow5(-e2) - 1).
            let q = log10_pow5(-e2) - (-e2 > 1) as u32;
            e10 = q as i32 + e2;
            let i = -e2 - q as i32;
            let k = pow5bits(i) - DOUBLE_POW5_BITCOUNT;
            let j = q as i32 - k;
            vr = unsafe {
                mul_shift_all_64(
                    m2,
                    #[cfg(feature = "small")]
                    &compute_pow5(i as u32),
                    #[cfg(not(feature = "small"))]
                    {
                        debug_assert!(i < DOUBLE_POW5_SPLIT.len() as i32);
                        DOUBLE_POW5_SPLIT.get_unchecked(i as usize)
                    },
                    j as u32,
                    #[cfg(maybe_uninit)]
                    {
                        vp_uninit.as_mut_ptr()
                    },
                    #[cfg(not(maybe_uninit))]
                    {
                        &mut vp
                    },
                    #[cfg(maybe_uninit)]
                    {
                        vm_uninit.as_mut_ptr()
                    },
                    #[cfg(not(maybe_uninit))]
                    {
                        &mut vm
                    },
                    mm_shift,
                )
            };
            #[cfg(maybe_uninit)]
            {
                vp = unsafe { vp_uninit.assume_init() };
                vm = unsafe { vm_uninit.assume_init() };
            }
            if q <= 1 {
                // {vr,vp,vm} is trailing zeros if {mv,mp,mm} has at least q trailing 0 bits.
                // mv = 4 * m2, so it always has at least two trailing 0 bits.
                vr_is_trailing_zeros = true;
                if accept_bounds {
                    // mm = mv - 1 - mm_shift, so it has 1 trailing 0 bit iff mm_shift == 1.
                    vm_is_trailing_zeros = mm_shift == 1;
                } else {
                    // mp = mv + 2, so it always has at least one trailing 0 bit.
                    vp -= 1;
                }
            } else if q < 63 {
                // TODO(ulfjack): Use a tighter bound here.
                // We want to know if the full product has at least q trailing zeros.
                // We need to compute min(p2(mv), p5(mv) - e2) >= q
                // <=> p2(mv) >= q && p5(mv) - e2 >= q
                // <=> p2(mv) >= q (because -e2 >= q)
                vr_is_trailing_zeros = multiple_of_power_of_2(mv, q);
            }
        }

        // Step 4: Find the shortest decimal representation in the interval of valid representations.
        let mut removed = 0i32;
        let mut last_removed_digit = 0u8;
        // On average, we remove ~2 digits.
        let output = if vm_is_trailing_zeros || vr_is_trailing_zeros {
            // General case, which happens rarely (~0.7%).
            loop {
                let vp_div10 = div10(vp);
                let vm_div10 = div10(vm);
                if vp_div10 <= vm_div10 {
                    break;
                }
                let vm_mod10 = (vm as u32).wrapping_sub(10u32.wrapping_mul(vm_div10 as u32));
                let vr_div10 = div10(vr);
                let vr_mod10 = (vr as u32).wrapping_sub(10u32.wrapping_mul(vr_div10 as u32));
                vm_is_trailing_zeros &= vm_mod10 == 0;
                vr_is_trailing_zeros &= last_removed_digit == 0;
                last_removed_digit = vr_mod10 as u8;
                vr = vr_div10;
                vp = vp_div10;
                vm = vm_div10;
                removed += 1;
            }
            if vm_is_trailing_zeros {
                loop {
                    let vm_div10 = div10(vm);
                    let vm_mod10 = (vm as u32).wrapping_sub(10u32.wrapping_mul(vm_div10 as u32));
                    if vm_mod10 != 0 {
                        break;
                    }
                    let vp_div10 = div10(vp);
                    let vr_div10 = div10(vr);
                    let vr_mod10 = (vr as u32).wrapping_sub(10u32.wrapping_mul(vr_div10 as u32));
                    vr_is_trailing_zeros &= last_removed_digit == 0;
                    last_removed_digit = vr_mod10 as u8;
                    vr = vr_div10;
                    vp = vp_div10;
                    vm = vm_div10;
                    removed += 1;
                }
            }
            if vr_is_trailing_zeros && last_removed_digit == 5 && vr % 2 == 0 {
                // Round even if the exact number is .....50..0.
                last_removed_digit = 4;
            }
            // We need to take vr + 1 if vr is outside bounds or we need to round up.
            vr + ((vr == vm && (!accept_bounds || !vm_is_trailing_zeros)) || last_removed_digit >= 5)
                as u64
        } else {
            // Specialized for the common case (~99.3%). Percentages below are relative to this.
            let mut round_up = false;
            let vp_div100 = div100(vp);
            let vm_div100 = div100(vm);
            // Optimization: remove two digits at a time (~86.2%).
            if vp_div100 > vm_div100 {
                let vr_div100 = div100(vr);
                let vr_mod100 = (vr as u32).wrapping_sub(100u32.wrapping_mul(vr_div100 as u32));
                round_up = vr_mod100 >= 50;
                vr = vr_div100;
                vp = vp_div100;
                vm = vm_div100;
                removed += 2;
            }
            // Loop iterations below (approximately), without optimization above:
            // 0: 0.03%, 1: 13.8%, 2: 70.6%, 3: 14.0%, 4: 1.40%, 5: 0.14%, 6+: 0.02%
            // Loop iterations below (approximately), with optimization above:
            // 0: 70.6%, 1: 27.8%, 2: 1.40%, 3: 0.14%, 4+: 0.02%
            loop {
                let vp_div10 = div10(vp);
                let vm_div10 = div10(vm);
                if vp_div10 <= vm_div10 {
                    break;
                }
                let vr_div10 = div10(vr);
                let vr_mod10 = (vr as u32).wrapping_sub(10u32.wrapping_mul(vr_div10 as u32));
                round_up = vr_mod10 >= 5;
                vr = vr_div10;
                vp = vp_div10;
                vm = vm_div10;
                removed += 1;
            }
            // We need to take vr + 1 if vr is outside bounds or we need to round up.
            vr + (vr == vm || round_up) as u64
        };
        let exp = e10 + removed;

        FloatingDecimal64 {
            exponent: exp,
            mantissa: output,
        }
    }