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    // Copyright 2015 The Ramp Developers
    //
    //    Licensed under the Apache License, Version 2.0 (the "License");
    //    you may not use this file except in compliance with the License.
    //    You may obtain a copy of the License at
    //
    //        http://www.apache.org/licenses/LICENSE-2.0
    //
    //    Unless required by applicable law or agreed to in writing, software
    //    distributed under the License is distributed on an "AS IS" BASIS,
    //    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    //    See the License for the specific language governing permissions and
    //    limitations under the License.

    /*!
     * Base conversion utilities
     *
     * Provides functions for converting an integer to/from a given base. In both `to_base` and
     * `from_base` the base-N output or input (respectively) is stored as raw bytes. That means that a
     * base-10 input contains bytes each with a value from 0-9.
     */

    use std::intrinsics::assume;

    use ll;
    use ll::limb::Limb;
    use ll::limb_ptr::{Limbs, LimbsMut};

    /// Information for converting to/from a given base, B. Stored in a table generated
    /// by build.rs
    struct Base {
        /// Number of digits a limb can hold in a given base. Except if B is a power of 2,
        /// in which case it is equal to the number of bits per digit in base B
        digits_per_limb: u32,
        /// The "big base", essentially the largest B^m that will fit in a limb.
        /// Should be the same as B^digits_per_limb
        big_base: Limb,
    }
    // Include BASES table
    include!(concat!(env!("OUT_DIR"), "/bases_table.rs"));

    #[inline(always)]
    fn div_unnorm(n: Limb, d: Limb) -> (Limb, Limb) {
        (n / d, n % d)
    }

    #[inline]
    pub unsafe fn num_base_digits(p: Limbs, n: i32, base: u32) -> usize {
        debug_assert!(base >= 2);
        assume(base >= 2);

        if n == 0 { return 1; }

        let cnt = (*p.offset((n - 1) as isize)).leading_zeros() as usize;
        let total_bits = (Limb::BITS * (n as usize)) - cnt;

        if base == 2 {
            // no need to do anything complicated here at all, so let's go
            // as fast as possible (this is a somewhat common case, due to
            // `bit_length`)
            total_bits
        } else if base.is_power_of_two() {
            let big_base = BASES.get_unchecked(base as usize).big_base.0 as usize;
            // doing an actual division here is much slower than this
            (total_bits + big_base - 1) >> big_base.trailing_zeros()
        } else {
            // Not sure if using floating-point arithmetic here is the best idea,
            // but it should be a reasonable accurate result, maybe a little high
            let total_bits = total_bits as f64;

            let lg2b = (base as f64).log2();
            let digits = total_bits / lg2b;
            return 1 + digits.ceil() as usize;
        }
    }

    #[inline]
    pub fn base_digits_to_len(num: usize, base: u32) -> usize {
        debug_assert!(base >= 2);

        if num == 0 { return 0; }

        let digits_per_limb = BASES[base as usize].digits_per_limb as usize;

        (num / digits_per_limb) + 1
    }

    /**
     * Converts `nn` limbs at `np` to the given base, storing the output in `out`. `out` is assumed to
     * have enough space for the entire digit. The output is stored from most-significant digit to least.
     *
     * The values in `out` are the raw values of the base. Conversion for output should be done as a second
     * step.
     */
    pub unsafe fn to_base<F: FnMut(u8)>(base: u32, np: Limbs, nn: i32, mut out_byte: F) {
        debug_assert!(nn >= 0);
        debug_assert!(base < BASES.len() as u32);
        debug_assert!(base >= 2);
        assume(base < BASES.len() as u32);
        assume(base >= 2);

        if nn <= 0 {
            out_byte(0);
            return;
        }
        // Fast path for powers-of-two, since each limb is already in base B^m format
        if base.is_power_of_two() {
            let bits_per_digit = BASES.get_unchecked(base as usize).big_base.0 as usize;
            assume(bits_per_digit > 0);

            let mut n1 = *np.offset((nn - 1) as isize);
            let cnt = n1.leading_zeros() as usize;

            let mut bits = Limb::BITS * (nn as usize) - cnt;
            let cnt = bits % bits_per_digit;
            if cnt != 0 {
                bits += bits_per_digit - cnt;
            }

            let mut bit_pos : isize = (bits - (nn as usize - 1) * Limb::BITS) as isize;

            let mut i = nn - 1;
            // Convert each limb by shifting and masking to get the value for each output digit
            loop {
                bit_pos -= bits_per_digit as isize;
                while bit_pos >= 0 {
                    let b = ((n1 >> (bit_pos as usize)) & ((Limb(1) << bits_per_digit) - 1)).0 as u8;
                    out_byte(b);
                    bit_pos -= bits_per_digit as isize;
                }
                i -= 1;
                if i < 0 { break; }

                let n0 = (n1 << ((-bit_pos) as usize)) & ((Limb(1) << bits_per_digit) - 1);
                n1 = *np.offset(i as isize);
                bit_pos += Limb::BITS as isize;
                // We have a potential overlap of bits, so get the value of the digit
                // that spans the two limbs.
                // The specific situation is (using 8-bit limbs as demonstration):
                //
                //    bbbbbbbb bbbbbbbb
                //          ^---^         Bits for next digit
                let b = (n0 | (n1 >> (bit_pos as usize))).0 as u8;
                out_byte(b);
            }
            return;
        }
        // TODO: Use divide-and-conquer for large numbers
        to_base_impl(0, base, np, nn, out_byte);
    }

    unsafe fn to_base_impl<F: FnMut(u8)>(mut len: u32, base: u32, np: Limbs, mut nn: i32, mut out_byte: F) {
        debug_assert!(base > 2);

        let buf_len = num_base_digits(np, nn, base);
        let mut buf : Vec<u8> = vec![0; buf_len];
        let mut r : Vec<Limb> = vec![Limb(0); (nn + 1) as usize];
        let rp = LimbsMut::new(&mut r[0], 0, r.len() as i32);

        ll::copy_incr(np, rp.offset(1), nn);

        let mut sz = 0;

        let s : *mut u8 = &mut buf[0];
        let mut s = s.offset(buf_len as isize);

        let base = Limb(base as ll::limb::BaseInt);

        macro_rules! base_impl (
            ($base:expr, $s:expr, $rp:expr, $sz:ident, $nn:ident) => (
                {
                    let digits_per_limb = BASES.get_unchecked($base.0 as usize).digits_per_limb;
                    let big_base = BASES.get_unchecked($base.0 as usize).big_base;

                    // Process limbs from least-significant to most, until there is only one
                    // limb left
                    while $nn > 1 {
                        // Divide rp by the big_base, with a single fractional limb produced.
                        // The fractional limb is approximately 1/remainder
                        ll::divrem_1($rp, 1, $rp.offset(1).as_const(), $nn, big_base);

                        $nn -= if *$rp.offset($nn as isize) == 0 { 1 } else { 0 };
                        let mut frac = *$rp + 1;
                        // The loop below produces digits from most-significant to least, but
                        // the containing loop works from least signficant limb up, so move
                        // the first position for the output for this limb. Since we know
                        // there is at least one more limb to process after this one, it's
                        // safe to output all digits that may be produced.
                        $s = $s.offset(-(digits_per_limb as isize));
                        let mut i = digits_per_limb;
                        loop {
                            // Multiply the fraction from divrem by the base, the overflow
                            // amount is the next digit we want
                            let (digit, f) = frac.mul_hilo($base);
                            frac = f;
                            *$s = digit.0 as u8;
                            $s = $s.offset(1);

                            $sz += 1;

                            i -= 1;
                            if i == 0 { break; }
                        }

                        $s = $s.offset(-(digits_per_limb as isize));
                    }

                    // Last limb, use normal conversion for this one so we
                    // don't overshoot the number of digits
                    let mut ul = *$rp.offset(1);
                    while ul != 0 {
                        let (q, r) = div_unnorm(ul, base);
                        $s = $s.offset(-1);
                        *$s = r.0 as u8;
                        ul = q;

                        $sz += 1;
                    }
                }
            )
        );

        // Specialise on the base-10 conversion routine. The other common base, 16, is handled
        // by the power-of-two case in to_base. This allows the compiler to unroll the inner
        // loop in the conversion, which is a sigificant speed increase.
        if base == 10 {
            base_impl!(Limb(10), s, rp, sz, nn);
        } else {
            base_impl!(base, s, rp, sz, nn);
        }

        let mut l = sz;

        // Output any leading zeros we may want
        while l < len {
            out_byte(0);
            len -= 1;
        }

        // Copy the temporary buffer into the output string
        while l != 0 {
            out_byte(*s);
            s = s.offset(1);
            l -= 1;
        }
    }

    /**
     * Converts the base `base` bytestring {bp, bs}, storing the limbs in `out`. `out` is assumed to
     * have enough space to store the result.
     */
    pub unsafe fn from_base(mut out: LimbsMut, bp: *const u8, bs: i32, base: u32) -> usize {
        debug_assert!(bs > 0);
        debug_assert!(base < BASES.len() as u32);
        debug_assert!(base >= 2);
        assume(base < BASES.len() as u32);
        assume(base >= 2);

        if bs <= 0 {
            *out = Limb(0);
            return 1;
        }

        if base.is_power_of_two() {
            let bits_per_digit = BASES.get_unchecked(base as usize).big_base.0 as usize;
            assume(bits_per_digit > 0);

            let mut size = 0;

            let mut b = bp.offset((bs - 1) as isize);
            let mut res_digit = Limb(0);
            let mut next_bitpos = 0;
            while b >= bp {
                let digit = Limb((*b) as ll::limb::BaseInt);

                res_digit = res_digit | (digit << next_bitpos);
                next_bitpos += bits_per_digit;
                if next_bitpos >= Limb::BITS {
                    next_bitpos -= Limb::BITS;
                    *out.offset(size as isize) = res_digit;
                    size += 1;
                    res_digit = digit >> (bits_per_digit - next_bitpos);
                }

                b = b.offset(-1);
            }

            if res_digit > 0 {
                *out.offset(size as isize) = res_digit;
                size += 1;
            }

            return size;
        }

        // TODO, use a divide-and-conquer algorithm for large inputs
        from_base_small(out, bp, bs, base)
    }

    unsafe fn from_base_small(mut out: LimbsMut, mut bp: *const u8, bs: i32, base: u32) -> usize {
        debug_assert!(base > 2);
        assume(base > 2);

        let big_base = BASES.get_unchecked(base as usize).big_base;
        let digits_per_limb = BASES.get_unchecked(base as usize).digits_per_limb;

        let mut i = digits_per_limb;
        let mut size : usize = 0;
        while i < (bs as u32) {
            let mut res_digit = Limb((*bp) as ll::limb::BaseInt);
            bp = bp.offset(1);

            if base == 10 {
                let mut j = digits_per_limb - 1;
                while j > 0 {
                    res_digit = res_digit * 10 + ((*bp) as ll::limb::BaseInt);
                    bp = bp.offset(1);
                    j -= 1;
                }
            } else {
                let mut j = digits_per_limb - 1;
                while j > 0 {
                    res_digit = res_digit * (base as ll::limb::BaseInt) + ((*bp) as ll::limb::BaseInt);
                    bp = bp.offset(1);
                    j -= 1;
                }
            }

            if size == 0 {
                if res_digit != 0 {
                    *out = res_digit;
                    size = 1;
                }
            } else {
                let mut carry = ll::mul_1(out, out.as_const(), size as i32, big_base);
                carry = carry + ll::add_1(out, out.as_const(), size as i32, res_digit);
                if carry != 0 {
                    *out.offset(size as isize) = carry;
                    size += 1;
                }
            }

            i += digits_per_limb;
        }

        let mut big_base = base as ll::limb::BaseInt;
        let mut res_digit = Limb((*bp) as ll::limb::BaseInt);
        bp = bp.offset(1);

        if base == 10 {
            let mut j = (bs as u32) - (i - digits_per_limb) - 1;
            while j > 0 {
                res_digit = res_digit * 10 + ((*bp) as ll::limb::BaseInt);
                big_base *= 10;
                bp = bp.offset(1);
                j -= 1;
            }
        } else {
            let mut j = (bs as u32) - (i - digits_per_limb) - 1;
            while j > 0 {
                res_digit = res_digit * (base as ll::limb::BaseInt) + ((*bp) as ll::limb::BaseInt);
                bp = bp.offset(1);
                big_base *= base as ll::limb::BaseInt;
                j -= 1;
            }
        }

        if size == 0 {
            if res_digit != 0 {
                *out = res_digit;
                size = 1;
            }
        } else {
            let mut carry = ll::mul_1(out, out.as_const(), size as i32, Limb(big_base));
            carry = carry + ll::add_1(out, out.as_const(), size as i32, res_digit);
            if carry != 0 {
                *out.offset(size as isize) = carry;
                size += 1;
            }
        }

        return size;
    }

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