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