syn/
bigint.rs

1use std::ops::{AddAssign, MulAssign};
2
3// For implementing base10_digits() accessor on LitInt.
4pub(crate) struct BigInt {
5    digits: Vec<u8>,
6}
7
8impl BigInt {
9    pub(crate) fn new() -> Self {
10        BigInt { digits: Vec::new() }
11    }
12
13    pub(crate) fn to_string(&self) -> String {
14        let mut repr = String::with_capacity(self.digits.len());
15
16        let mut has_nonzero = false;
17        for digit in self.digits.iter().rev() {
18            has_nonzero |= *digit != 0;
19            if has_nonzero {
20                repr.push((*digit + b'0') as char);
21            }
22        }
23
24        if repr.is_empty() {
25            repr.push('0');
26        }
27
28        repr
29    }
30
31    fn reserve_two_digits(&mut self) {
32        let len = self.digits.len();
33        let desired =
34            len + !self.digits.ends_with(&[0, 0]) as usize + !self.digits.ends_with(&[0]) as usize;
35        self.digits.resize(desired, 0);
36    }
37}
38
39impl AddAssign<u8> for BigInt {
40    // Assumes increment <16.
41    fn add_assign(&mut self, mut increment: u8) {
42        self.reserve_two_digits();
43
44        let mut i = 0;
45        while increment > 0 {
46            let sum = self.digits[i] + increment;
47            self.digits[i] = sum % 10;
48            increment = sum / 10;
49            i += 1;
50        }
51    }
52}
53
54impl MulAssign<u8> for BigInt {
55    // Assumes base <=16.
56    fn mul_assign(&mut self, base: u8) {
57        self.reserve_two_digits();
58
59        let mut carry = 0;
60        for digit in &mut self.digits {
61            let prod = *digit * base + carry;
62            *digit = prod % 10;
63            carry = prod / 10;
64        }
65    }
66}
syn/bigint.rs

syn/
bigint.rs
