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use num_traits::{One, Zero};
use smallvec::SmallVec;
use std::cmp::Ordering;
use crate::algorithms::{add2, cmp_slice, sub2};
use crate::big_digit::{self, BigDigit, DoubleBigDigit};
use crate::BigUint;
pub fn div_rem_digit(mut a: BigUint, b: BigDigit) -> (BigUint, BigDigit) {
let mut rem = 0;
for d in a.data.iter_mut().rev() {
let (q, r) = div_wide(rem, *d, b);
*d = q;
rem = r;
}
(a.normalized(), rem)
}
#[inline]
pub fn div_wide(hi: BigDigit, lo: BigDigit, divisor: BigDigit) -> (BigDigit, BigDigit) {
debug_assert!(hi < divisor);
let lhs = big_digit::to_doublebigdigit(hi, lo);
let rhs = divisor as DoubleBigDigit;
((lhs / rhs) as BigDigit, (lhs % rhs) as BigDigit)
}
pub fn div_rem(u: &BigUint, d: &BigUint) -> (BigUint, BigUint) {
if d.is_zero() {
panic!()
}
if u.is_zero() {
return (Zero::zero(), Zero::zero());
}
if d.data.len() == 1 {
if d.data[0] == 1 {
return (u.clone(), Zero::zero());
}
let (div, rem) = div_rem_digit(u.clone(), d.data[0]);
return (div, rem.into());
}
match u.cmp(d) {
Ordering::Less => return (Zero::zero(), u.clone()),
Ordering::Equal => return (One::one(), Zero::zero()),
Ordering::Greater => {}
}
let shift = d.data.last().unwrap().leading_zeros() as usize;
let mut a = u << shift;
let b = d << shift;
let bn = *b.data.last().unwrap();
let q_len = a.data.len() - b.data.len() + 1;
let mut q = BigUint {
data: smallvec![0; q_len],
};
let mut tmp = BigUint {
data: SmallVec::with_capacity(2),
};
for j in (0..q_len).rev() {
let offset = j + b.data.len() - 1;
if offset >= a.data.len() {
continue;
}
let mut a0 = tmp;
a0.data.truncate(0);
a0.data.extend(a.data[offset..].iter().cloned());
let (mut q0, _) = div_rem_digit(a0, bn);
let mut prod = &b * &q0;
while cmp_slice(&prod.data[..], &a.data[j..]) == Ordering::Greater {
let one: BigUint = One::one();
q0 = q0 - one;
prod = prod - &b;
}
add2(&mut q.data[j..], &q0.data[..]);
sub2(&mut a.data[j..], &prod.data[..]);
a.normalize();
tmp = q0;
}
debug_assert!(a < b);
(q.normalized(), a >> shift)
}