// 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::d2s;

pub const FLOAT_POW5_INV_BITCOUNT: i32 = d2s::DOUBLE_POW5_INV_BITCOUNT - 64;

pub const FLOAT_POW5_BITCOUNT: i32 = d2s::DOUBLE_POW5_BITCOUNT - 64;

#[cfg_attr(feature = "no-panic", inline)]

fn pow5factor_32(mut value: u32) -> u32 {

    let mut count = 0u32;

    loop {

        debug_assert!(value != 0);

        let q = value / 5;

        let r = value % 5;

        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_32(value: u32, p: u32) -> bool {

    pow5factor_32(value) >= p

}

// Returns true if value is divisible by 2^p.

#[cfg_attr(feature = "no-panic", inline)]

pub fn multiple_of_power_of_2_32(value: u32, p: u32) -> bool {

    // __builtin_ctz doesn't appear to be faster here.

    (value & ((1u32 << p) - 1)) == 0

}

// It seems to be slightly faster to avoid uint128_t here, although the

// generated code for uint128_t looks slightly nicer.

#[cfg_attr(feature = "no-panic", inline)]

fn mul_shift_32(m: u32, factor: u64, shift: i32) -> u32 {

    debug_assert!(shift > 32);

    // The casts here help MSVC to avoid calls to the __allmul library

    // function.

    let factor_lo = factor as u32;

    let factor_hi = (factor >> 32) as u32;

    let bits0 = m as u64 * factor_lo as u64;

    let bits1 = m as u64 * factor_hi as u64;

    let sum = (bits0 >> 32) + bits1;

    let shifted_sum = sum >> (shift - 32);

    debug_assert!(shifted_sum <= u32::max_value() as u64);

    shifted_sum as u32

}

#[cfg_attr(feature = "no-panic", inline)]

pub fn mul_pow5_inv_div_pow2(m: u32, q: u32, j: i32) -> u32 {

    #[cfg(feature = "small")]

    {

        // The inverse multipliers are defined as [2^x / 5^y] + 1; the upper 64

        // bits from the double lookup table are the correct bits for [2^x /

        // 5^y], so we have to add 1 here. Note that we rely on the fact that

        // the added 1 that's already stored in the table never overflows into

        // the upper 64 bits.

        let pow5 = unsafe { d2s::compute_inv_pow5(q) };

        mul_shift_32(m, pow5.1 + 1, j)

    }

    #[cfg(not(feature = "small"))]

    {

        debug_assert!(q < d2s::DOUBLE_POW5_INV_SPLIT.len() as u32);

        unsafe {

            mul_shift_32(

                m,

                d2s::DOUBLE_POW5_INV_SPLIT.get_unchecked(q as usize).1 + 1,

                j,

            )

        }

    }

}

#[cfg_attr(feature = "no-panic", inline)]

pub fn mul_pow5_div_pow2(m: u32, i: u32, j: i32) -> u32 {

    #[cfg(feature = "small")]

    {

        let pow5 = unsafe { d2s::compute_pow5(i) };

        mul_shift_32(m, pow5.1, j)

    }

    #[cfg(not(feature = "small"))]

    {

        debug_assert!(i < d2s::DOUBLE_POW5_SPLIT.len() as u32);

        unsafe { mul_shift_32(m, d2s::DOUBLE_POW5_SPLIT.get_unchecked(i as usize).1, j) }

    }

}