//! C Interfaces and Implementations: Techniques for Creating Reusable Software [Hanson 1996-08-30]
//!

use std::cmp::Ordering;
#[cfg(test)]
mod test;
/// An extended-iprecision unsigned integer is represented in base by an
/// array of n digits, least significant digit first. Most XP functions take n as
/// an argument along with source and destination Ts; it is SAD for n<1 or
/// for n not to be the length of the corresponding Ts. It is SAD to pass a
/// null T or a T that is too small to any XP function.
pub type XP = [u8];

macro_rules! base {
    () => {
        256
    };
}
/// sets z[0..n-1] to u mod 2⁸ⁿ and returns u/2⁸ⁿ.
pub const fn from_int(n: u32, z: &mut XP, mut u: u128) -> u128 {
    let mut i = 0;
    let n = n as usize;
    while {
        z[i] = (u % base!()) as u8;
        i += 1;

        u /= base!();
        u > 0 && i < n
    } {}
    while i < n {
        z[i] = 0;
        i += 1;
    }
    u
}
/// returns x mod (ULONG_MAX+1).
pub const fn to_int(n: u32, x: &XP) -> u128 {
    let mut u = 0;
    let mut i = size_of::<u128>().min(n as usize);

    while i > 0 {
        i -= 1;
        u = base!() * u + x[i] as u128;
    }
    u
}
/// returns the length of x; that is, the index plus one of the most signifi-
/// cant nonzero digit in x[0..n-1].
pub const fn len(mut n: u32, x: &XP) -> u32 {
    while (n > 1 && x[n as usize - 1] == 0) {
        n -= 1;
    }
    n
}
macro_rules! u1 {
    ($x:expr) => {
        match $x {
            0 => false,
            1 => true,
            _ => panic!("not u1"),
        }
    };
}

/// sets z[0..n-1] to x + y + carry and returns the carry out of z[n-1].
pub const fn add(n: u32, z: &mut XP, x: &XP, y: &XP, carry: bool) -> bool {
    let mut carry = carry as usize;
    let mut i = 0;
    while i < n as usize {
        carry += x[i] as usize + y[i] as usize;
        z[i] = (carry % base!()) as u8;
        carry /= base!();

        i += 1;
    }
    u1!(carry)
}
/// sets z[0..n-1] to x − y − borrow and returns the borrow into z[n-1].
pub const fn sub(
    n: u32,
    z: &mut XP,
    x: &XP,
    y: &XP,
    borrow: bool,
) -> bool {
    let mut i = 0;
    let mut borrow = borrow as u32;
    while i < n as usize {
        let mut d = (x[i] as u32 + base!()) - borrow - y[i] as u32;
        z[i] = (d % base!()) as u8;
        borrow = 1 - (d / base!());
        i += 1;
    }
    u1!(borrow)
}
#[doc(hidden)]
pub const unsafe fn subp(
    n: u32,
    z: *mut u8,
    x: *const u8,
    y: *const u8,
    borrow: bool,
) -> bool {
    let mut i = 0;
    let mut borrow = borrow as u32;
    while i < n as usize {
        let mut d =
            (*x.add(i) as u32 + base!()) - borrow - *y.add(i) as u32;
        *z.add(i) = (d % base!()) as u8;
        borrow = 1 - (d / base!());
        i += 1;
    }
    u1!(borrow)
}
/// sets z[0..n-1] to x + y, where y is a single digit, and returns the carry-out of z[n-1].
pub const fn sum(n: u32, z: &mut XP, x: &XP, mut y: u8) -> u8 {
    unsafe { sum_p(n, z.as_mut_ptr(), x.as_ptr(), y) }
}
#[doc(hidden)]
pub const unsafe fn sum_p(
    n: u32,
    z: *mut u8,
    x: *const u8,
    mut y: u8,
) -> u8 {
    let mut i = 0;
    let mut y = y as u32;
    while i < n as usize {
        y += *x.add(i) as u32;
        *z.add(i) = (y % base!()) as u8;
        y /= base!();
        i += 1;
    }
    y as u8
}
/// sets z[0..n-1] to x − y, where y is a single digit, and returns the borrow into z[n-1].
pub const fn diff(n: u32, z: &mut XP, x: &XP, y: u8) -> u8 {
    let mut y = y as u32;
    let mut i = 0;
    while i < n as usize {
        let d = (x[i] as u32 + base!()) - y;
        z[i] = (d % base!()) as u8;
        y = 1 - d / base!();
        i += 1;
    }
    y as u8
}
/// sets z[0..n-1] to !x + carry, where carry is zero or one, and returns
/// the carry-out of z[n-1].
pub const fn neg(n: u32, z: &mut XP, x: &XP, carry: bool) -> bool {
    let mut carry = carry as u32;
    let mut i = 0;
    while i < n as usize {
        carry += (!x[i]) as u32;
        z[i] = (carry % base!()) as u8;
        carry /= base!();
        i += 1;
    }
    u1!(carry)
}
/// adds x[0..n-1]•y[0..m-1] to z[0..n+m-1] and returns the carry-out of
/// z[n+m-1]. If z=0, Xmul computes x•y. It is SAD for z to be the same T as x or y.
pub const fn mul(z: &mut XP, n: u32, x: &XP, m: u32, y: &XP) -> u32 {
    let (mut i, mut carryout) = (0, 0);
    while i < n as usize {
        let mut carry = 0;
        let mut j = 0;
        while j < m as usize {
            carry += x[i as usize] as u32 * y[j as usize] as u32
                + z[i + j] as u32;
            z[i + j] = (carry % base!()) as u8;
            carry /= base!();
            j += 1;
        }
        while j < (n as usize + m as usize - i) {
            carry += z[i + j] as u32;
            z[i + j] = (carry % base!()) as u8;
            carry /= base!();
            j += 1;
        }
        assert!(carry == 0 || carry == 1);
        carryout |= carry;
        i += 1;
    }
    carryout
}

const unsafe fn quot_p(n: u32, z: *mut u8, x: *const u8, y: u8) -> u8 {
    let mut i = n as isize - 1;
    let mut carry = 0;

    while i >= 0 {
        carry = carry * base!() + (*x.add(i as _)) as u32;
        *z.add(i as _) = (carry / y as u32) as _;
        carry %= y as u32;
        i -= 1;
    }
    carry as u8
}
/// sets z[0..n-1] to x/y, where y is a single digit, and returns x mod y. It
/// is SAD for y=0
pub const fn quot(n: u32, z: &mut XP, x: &XP, y: u8) -> u8 {
    unsafe { quot_p(n, z.as_mut_ptr(), x.as_ptr(), y) }
}
/// XP_product sets z[0..n-1] to x•y and returns the carry-out of the
/// most significant digit; the carry can be as large as 2^8- XP_quotient
/// sets z[0..n-1] to x/y and returns the remainder, x mod y; the remainder
/// can be as large as . For XP_product and XP_quotient, y must not
/// exceed − 1.
pub const fn product(n: u32, z: &mut XP, x: &XP, y: u8) -> u8 {
    unsafe { product_p(n, z.as_mut_ptr(), x.as_ptr(), y) }
}
const unsafe fn product_p(n: u32, z: *mut u8, x: *const u8, y: u8) -> u8 {
    let mut i = 0;
    let mut carry = 0;
    while i < n as usize {
        carry += *x.add(i) as u32 * y as u32;
        *z.add(i) = (carry % base!()) as u8;
        carry /= base!();
        i += 1;
    }
    carry.try_into().ok().unwrap()
}
/// sets q[0..n-1] to x[0..n-1]/y[0..m-1], r[0..m-1] to x[0..n-1] mod
/// y[0..m-1]. If y=0, panics.
/// tmp must hold at least n+m+2 digits. It is unexpected
/// for q or r to be one of x or y, for q and r to be the same T, or for
/// tmp to be too small
pub const fn div(
    mut n: u32,
    q: &mut XP,
    x: &XP,
    mut m: u32,
    y: &XP,
    r: &mut XP,
    tmp: &mut XP,
) {
    let nx = n;
    let my = m;
    n = len(n, x);
    m = len(m, y);
    if m == 1 {
        if (y[0] == 0) {
            panic!()
        }
        r[0] = quot(nx, q, x, y[0] as _);
        let mut i = 0;
        while i < my as usize - 1 {
            r[1 + i] = 0;
            i += 1;
        }
    } else if m > n {
        let mut i = 0;
        while i < nx as usize {
            q[i] = 0;
            i += 1;
        }
        r[..n as usize].copy_from_slice(&x[..n as usize]);
        let mut i = 0;
        while i < my - n {
            r[(n + i) as usize] = 0;
            i += 1;
        }
    } else {
        let (rem, dq) = tmp.split_at_mut(n as usize + 1);
        // let rem = &mut tmp[..n as usize];
        // let dq = &mut tmp[n as usize + 1..];
        assert!(2 <= m && m <= n);
        rem[..n as usize].copy_from_slice(&x[..n as usize]);
        rem[n as usize] = 0;
        let mut k = (n - m) as i32;
        while k >= 0 {
            let k_ = k as u32;
            let qk = {
                let i = 0;
                assert!(2 <= m && m <= k_ + m && k_ + m <= n);

                let mut qk = {
                    let km = (k_ + m) as usize;
                    let y2 = y[m as usize - 1] as u64 * base!() as u64
                        + y[m as usize - 2] as u64;
                    let r3 = rem[km] as u64 * (base!() * base!())
                        + rem[km - 1] as u64 * base!()
                        + rem[km - 2] as u64;
                    let mut qk = r3 / y2;
                    if (qk >= base!()) {
                        qk = base!() - 1
                    };
                    qk as u8
                };
                // qk  y[m-2..m-1]/rem[k+m-2..k+m] 314
                dq[m as usize] = product(m, dq, y, qk) as _;
                let mut i = m as i32;
                // ch
                while i > 0 && rem[(i + k) as usize] == dq[i as usize] {
                    i -= 1;
                }

                if (rem[(i + k) as usize] < dq[i as usize]) {
                    qk -= 1;
                    dq[m as usize] = product(m, dq, y, qk) as _;
                }
                qk
            };
            q[k as usize] = qk;
            {
                assert!(0 <= k && k <= k + m as i32);
                let borrow = unsafe {
                    subp(
                        m + 1,
                        rem.as_mut_ptr().add(k as _),
                        rem.as_ptr().add(k as _),
                        dq.as_ptr(),
                        false,
                    )
                };
                assert!(!borrow);
            }
            k -= 1;
        }
        r[..m as usize].copy_from_slice(&rem[..m as usize]);
        let mut i = n - m + 1;
        while i < nx {
            q[i as usize] = 0;
            i += 1;
        }
        let mut i = m;
        while i < my {
            r[i as usize] = 0;
            i += 1;
        }
        r[..m as usize].copy_from_slice(&rem[..m as usize]);
        // memcpy(r, rem, m);
    }
}

/// sets z[0..n-1] to x[0..m-1] shifted left by s bits, and fills the vacated
/// bits with fill, which must be zero or one. It is SADk for s<0.
pub const fn shl(
    n: u32,
    z: &mut XP,
    m: u32,
    x: &XP,
    mut s: u32,
    fill: u8,
) {
    assert!(matches!(fill, 0 | 0xff));
    let mut j = n as i32 - 1;
    let mut i = (if (n > m) { m - 1 } else { n - s / 8 - 1 }) as i32;
    while j >= (m + s / 8) as _ {
        z[j as usize] = 0;
        j -= 1;
    }
    //const fill when
    while i >= 0 {
        z[j as usize] = x[i as usize];
        j -= 1;
        i -= 1;
    }
    while j >= 0 {
        z[j as usize] = fill;
        j -= 1;
    }
    s %= 8;
    if s > 0 {
        unsafe { product_p(n, z.as_mut_ptr(), z.as_ptr(), 1 << s) };
        z[0] |= fill >> (8 - s);
    }
}
//// shifts right; see [`shl`]. If n>m, the excess bits are treated as if
/// they were equal to fill
pub const fn shr(
    n: u32,
    z: &mut XP,
    m: u32,
    x: &XP,
    s: u32,
    fill: u8,
) -> u8 {
    assert!(matches!(fill, 0 | 0xff));
    let mut i = s / 8;
    let mut j = 0;
    while i < m && j < n {
        z[j as usize] = x[i as usize];
        j += 1;
        i += 1;
    }
    while j < n {
        z[j as usize] = fill;
        j += 1;
    }
    let s = s % 8;
    if s > 0 {
        let r = unsafe { quot_p(n, z.as_mut_ptr(), z.as_ptr(), 1 << s) };
        z[n as usize - 1] |= fill << (8 - s);
        r
    } else {
        0
    }
}
/// interprets str as an unsigned integer in base using z[0..n-1] as the
/// initial value in the conversion, and returns the first nonzero carry-out
/// of the conversion step. If end≠null, *end points to the character in
/// str that terminated the scan or produced a nonzero carry.
const fn from_str(n: u32, z: &mut XP, base: u8, str: &[u8]) -> u8 {
    assert!(base < 36);
    let mut i = 0;
    while i < str.len() {
        let b = str[i];
        let b = match b {
            b'0'..=b'9' => b - b'0',
            b'a'..=b'z' => b - b'a',
            _ => return 255,
        };
        if b > base {
            return 255;
        }
        let c = unsafe { product_p(n, z.as_mut_ptr(), z.as_ptr(), base) };
        unsafe { sum_p(n, z.as_mut_ptr(), z.as_ptr(), b as _) };

        if c != 0 {
            return c;
        }

        i += 1;
    }
    0
}
/// fills str[0..size-1] with the character representation of x in base,
/// sets x to zero, and returns str. It is a panic for size to be
/// too small, or for base<2 or base>36.
pub const fn to_str<'a>(
    put_in: &'a mut Vec<u8>,
    base: u8,
    mut n: u32,
    x: &mut XP,
) -> &'a [u8] {
    let mut i = 0;
    assert!(base >= 2 && base <= 36);
    while {
        let r = unsafe { quot_p(n, x.as_mut_ptr(), x.as_ptr(), base) };
        put_in.push(b"0123456789abcdefghijklmnopqrstuvxyz"[r as usize]);
        i += 1;
        // str[i] = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ"[r];
        while n > 1 && x[n as usize - 1] == 0 {
            n -= 1;
        }
        n > 1 || x[0] != 0
    } {}

    put_in.as_mut_slice().reverse();
    put_in.as_slice()
}

/// x[..n] <=> y[..n]
pub const fn cmp(n: u32, x: &XP, y: &XP) -> Ordering {
    let mut i = n as i32 - 1;
    while (i > 0 && x[i as usize] == y[i as usize]) {
        i -= 1
    }
    x[i as usize].cmp(&y[i as usize])
}