| 1 | |
| 2 |
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| 3 | use std::ops::{AddAssign, MulAssign};
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| 4 |
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| 5 | |
| 6 | pub(crate) struct BigInt {
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| 7 | digits: Vec<u8>,
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| 8 | }
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| 9 |
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| 10 | impl BigInt {
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| 11 | pub(crate) fn new() -> Self {
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| 12 | BigInt { digits: Vec::new() }
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| 13 | }
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| 14 |
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| 15 | pub(crate) fn to_string(&self) -> String {
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| 16 | let mut repr = String::with_capacity(self.digits.len());
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| 17 |
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| 18 | let mut has_nonzero = false;
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| 19 | for digit in self.digits.iter().rev() {
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| 20 | has_nonzero |= *digit != 0;
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| 21 | if has_nonzero {
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| 22 | repr.push((*digit + b'0') as char);
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| 23 | }
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| 24 | }
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| 25 |
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| 26 | if repr.is_empty() {
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| 27 | repr.push('0');
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| 28 | }
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| 29 |
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| 30 | repr
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| 31 | }
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| 32 |
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| 33 | fn reserve_two_digits(&mut self) {
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| 34 | let len = self.digits.len();
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| 35 | let desired =
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| 36 | len + !self.digits.ends_with(&[0, 0]) as usize + !self.digits.ends_with(&[0]) as usize;
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| 37 | self.digits.resize(desired, 0);
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| 38 | }
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| 39 | }
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| 40 |
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| 41 | impl AddAssign<u8> for BigInt {
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| 42 | |
| 43 | fn add_assign(&mut self, mut increment: u8) {
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| 44 | self.reserve_two_digits();
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| 45 |
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| 46 | let mut i = 0;
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| 47 | while increment > 0 {
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| 48 | let sum = self.digits[i] + increment;
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| 49 | self.digits[i] = sum % 10;
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| 50 | increment = sum / 10;
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| 51 | i += 1;
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| 52 | }
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| 53 | }
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| 54 | }
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| 55 |
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| 56 | impl MulAssign<u8> for BigInt {
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| 57 | |
| 58 | fn mul_assign(&mut self, base: u8) {
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| 59 | self.reserve_two_digits();
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| 60 |
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| 61 | let mut carry = 0;
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| 62 | for digit in &mut self.digits {
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| 63 | let prod = *digit * base + carry;
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| 64 | *digit = prod % 10;
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| 65 | carry = prod / 10;
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| 66 | }
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| 67 | }
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| 68 | }
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