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use std::ops::{AddAssign, MulAssign};
// For implementing base10_digits() accessor on LitInt.
pub struct BigInt {
digits: Vec<u8>,
}
impl BigInt {
pub fn new() -> Self {
BigInt { digits: Vec::new() }
}
pub fn to_string(&self) -> String {
let mut repr = String::with_capacity(self.digits.len());
let mut has_nonzero = false;
for digit in self.digits.iter().rev() {
has_nonzero |= *digit != 0;
if has_nonzero {
repr.push((*digit + b'0') as char);
}
}
if repr.is_empty() {
repr.push('0');
}
repr
}
fn reserve_two_digits(&mut self) {
let len = self.digits.len();
let desired =
len + !self.digits.ends_with(&[0, 0]) as usize + !self.digits.ends_with(&[0]) as usize;
self.digits.resize(desired, 0);
}
}
impl AddAssign<u8> for BigInt {
// Assumes increment <16.
fn add_assign(&mut self, mut increment: u8) {
self.reserve_two_digits();
let mut i = 0;
while increment > 0 {
let sum = self.digits[i] + increment;
self.digits[i] = sum % 10;
increment = sum / 10;
i += 1;
}
}
}
impl MulAssign<u8> for BigInt {
// Assumes base <=16.
fn mul_assign(&mut self, base: u8) {
self.reserve_two_digits();
let mut carry = 0;
for digit in &mut self.digits {
let prod = *digit * base + carry;
*digit = prod % 10;
carry = prod / 10;
}
}
}
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