}
}
+// Subtract with carry, returning the difference and the carry
+fn overflowing_sub(a: u64, b: u64, carry: bool) -> (u64, bool) {
+ let diff = u64::wrapping_sub(a, b);
+ let carry_n = if carry { 1 } else { 0 };
+ if diff <= a { // the first diff did not wrap
+ let diff_total = u64::wrapping_sub(diff, carry_n);
+ let had_wrap = diff_total > diff;
+ (diff_total, had_wrap)
+ } else { // the first diff did wrap
+ // it is impossible for this to wrap again, as we are just substracting 0 or 1
+ (diff - carry_n, true)
+ }
+}
+
impl BigInt {
/// Construct a BigInt from a "small" one.
pub fn new(x: u64) -> Self {
other
} else {
// compare back-to-front, i.e., most significant digit first
- let mut idx = self.data.len()-1;
+ let mut idx = self.data.len();
while idx > 0 {
+ idx = idx-1;
if self.data[idx] < other.data[idx] {
return self;
} else if self.data[idx] > other.data[idx] {
return other;
}
- else {
- idx = idx-1;
- }
}
// the two are equal
return self;
}
}
+impl<'a, 'b> ops::Sub<&'a BigInt> for &'b BigInt {
+ type Output = BigInt;
+ fn sub(self, rhs: &'a BigInt) -> Self::Output {
+ let max_len = cmp::max(self.data.len(), rhs.data.len());
+ let mut result_vec:Vec<u64> = Vec::with_capacity(max_len);
+ let mut carry:bool = false; // the carry bit
+ for i in 0..max_len {
+ // compute next digit and carry
+ let lhs_val = if i < self.data.len() { self.data[i] } else { 0 };
+ let rhs_val = if i < rhs.data.len() { rhs.data[i] } else { 0 };
+ let (sum, new_carry) = overflowing_sub(lhs_val, rhs_val, carry);
+ // store them
+ result_vec.push(sum);
+ carry = new_carry;
+ }
+ if carry {
+ panic!("Wrapping subtraction of BigInt");
+ }
+ // We may have trailing zeroes, so get rid of them
+ BigInt::from_vec(result_vec)
+ }
+}
+
+impl<'a> ops::Sub<BigInt> for &'a BigInt {
+ type Output = BigInt;
+ #[inline]
+ fn sub(self, rhs: BigInt) -> Self::Output {
+ self - &rhs
+ }
+}
+
+impl<'a> ops::Sub<&'a BigInt> for BigInt {
+ type Output = BigInt;
+ #[inline]
+ fn sub(self, rhs: &'a BigInt) -> Self::Output {
+ &self - rhs
+ }
+}
+
+impl ops::Sub<BigInt> for BigInt {
+ type Output = BigInt;
+ #[inline]
+ fn sub(self, rhs: BigInt) -> Self::Output {
+ &self - &rhs
+ }
+}
+
#[cfg(test)]
mod tests {
use std::u64;
- use super::overflowing_add;
- use super::BigInt;
+ use super::{overflowing_add,overflowing_sub,BigInt,Minimum,vec_min};
+
+ #[test]
+ fn test_min() {
+ let b1 = BigInt::new(1);
+ let b2 = BigInt::new(42);
+ let b3 = BigInt::from_vec(vec![0, 1]);
+
+ assert_eq!(b1.min(&b2), &b1);
+ assert_eq!(b2.min(&b1), &b1);
+ assert_eq!(b3.min(&b2), &b2);
+ assert_eq!(b2.min(&b3), &b2);
+ }
+
+ #[test]
+ fn test_vec_min() {
+ let b1 = BigInt::new(1);
+ let b2 = BigInt::new(42);
+ let b3 = BigInt::from_vec(vec![0, 1]);
+
+ assert_eq!(vec_min(&vec![b2.clone(), b1.clone(), b3.clone()]), Some(&b1));
+ assert_eq!(vec_min(&vec![b2.clone(), b3.clone()]), Some(&b2));
+ assert_eq!(vec_min(&vec![b3.clone()]), Some(&b3));
+ assert_eq!(vec_min::<BigInt>(&vec![]), None);
+ }
#[test]
fn test_overflowing_add() {
assert_eq!(overflowing_add(1 << 63, (1 << 63) -1 , true), (0, true));
}
+ #[test]
+ fn test_overflowing_sub() {
+ assert_eq!(overflowing_sub(100, 10, false), (90, false));
+ assert_eq!(overflowing_sub(100, 10, true), (89, false));
+ assert_eq!(overflowing_sub(10, 1 << 63, false), ((1 << 63) + 10, true));
+ assert_eq!(overflowing_sub(10, 1 << 63, true), ((1 << 63) + 9, true));
+ assert_eq!(overflowing_sub(42, 42 , true), (u64::max_value(), true));
+ }
+
#[test]
fn test_add() {
let b1 = BigInt::new(1 << 32);
let b2 = BigInt::from_vec(vec![0, 1]);
+ let b3 = BigInt::from_vec(vec![0, 0, 1]);
+ let b4 = BigInt::new(1 << 63);
assert_eq!(&b1 + &b2, BigInt::from_vec(vec![1 << 32, 1]));
+ assert_eq!(&b2 + &b1, BigInt::from_vec(vec![1 << 32, 1]));
+ assert_eq!(&b2 + &b3, BigInt::from_vec(vec![0, 1, 1]));
+ assert_eq!(&b2 + &b3 + &b4 + &b4, BigInt::from_vec(vec![0, 2, 1]));
+ assert_eq!(&b2 + &b4 + &b3 + &b4, BigInt::from_vec(vec![0, 2, 1]));
+ assert_eq!(&b4 + &b2 + &b3 + &b4, BigInt::from_vec(vec![0, 2, 1]));
+ }
+
+ #[test]
+ fn test_sub() {
+ let b1 = BigInt::new(1 << 32);
+ let b2 = BigInt::from_vec(vec![0, 1]);
+ let b3 = BigInt::from_vec(vec![0, 0, 1]);
+ let b4 = BigInt::new(1 << 63);
+
+ assert_eq!(&b2 - &b1, BigInt::from_vec(vec![u64::max_value() - (1 << 32) + 1]));
+ assert_eq!(&b3 - &b2, BigInt::from_vec(vec![0, u64::max_value(), 0]));
+ assert_eq!(&b2 - &b4 - &b4, BigInt::new(0));
+ assert_eq!(&b3 - &b2 - &b4 - &b4, BigInt::from_vec(vec![0, u64::max_value() - 1]));
+ assert_eq!(&b3 - &b4 - &b2 - &b4, BigInt::from_vec(vec![0, u64::max_value() - 1]));
+ assert_eq!(&b3 - &b4 - &b4 - &b2, BigInt::from_vec(vec![0, u64::max_value() - 1]));
+ }
+
+ #[test]
+ #[should_panic(expected = "Wrapping subtraction of BigInt")]
+ fn test_sub_panic1() {
+ let _ = BigInt::new(1) - BigInt::new(5);
+ }
+
+ #[test]
+ #[should_panic(expected = "Wrapping subtraction of BigInt")]
+ fn test_sub_panic2() {
+ let _ = BigInt::from_vec(vec![5,8,3,33,1<<13,46,1<<49, 1, 583,1<<60,2533]) - BigInt::from_vec(vec![5,8,3,33,1<<13,46,1<<49, 5, 583,1<<60,2533]);
}
#[test]
projects / rust-101.git / blobdiff