// SPDX-License-Identifier: Apache-2.0 OR MIT use std::ops::{AddAssign, MulAssign}; // For implementing base10_digits() accessor on LitInt.pub(crate) struct BigInt {    digits: Vec<u8>,} impl BigInt {    pub(crate) fn new() -> Self {        BigInt { digits: Vec::new() }    }     pub(crate) 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;        }    }}