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Reorder ops in LCM to avoid overflow. Fix #166

This commit is contained in:
Felix S. Klock II 2016-02-17 22:52:52 +01:00
parent 7a33808b07
commit d298262573
1 changed files with 30 additions and 2 deletions
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32
src/integer.rs
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@ -259,7 +259,7 @@ macro_rules! impl_integer_for_isize {
#[inline] #[inline]
fn lcm(&self, other: &$T) -> $T { fn lcm(&self, other: &$T) -> $T {
// should not have to recalculate abs // should not have to recalculate abs
((*self * *other) / self.gcd(other)).abs() (*self * (*other / self.gcd(other))).abs()
} }
/// Deprecated, use `is_multiple_of` instead. /// Deprecated, use `is_multiple_of` instead.
@ -508,7 +508,7 @@ macro_rules! impl_integer_for_usize {
/// Calculates the Lowest Common Multiple (LCM) of the number and `other`. /// Calculates the Lowest Common Multiple (LCM) of the number and `other`.
#[inline] #[inline]
fn lcm(&self, other: &$T) -> $T { fn lcm(&self, other: &$T) -> $T {
(*self * *other) / self.gcd(other) *self * (*other / self.gcd(other))
} }
/// Deprecated, use `is_multiple_of` instead. /// Deprecated, use `is_multiple_of` instead.
@ -628,3 +628,31 @@ impl_integer_for_usize!(u16, test_integer_u16);
impl_integer_for_usize!(u32, test_integer_u32); impl_integer_for_usize!(u32, test_integer_u32);
impl_integer_for_usize!(u64, test_integer_u64); impl_integer_for_usize!(u64, test_integer_u64);
impl_integer_for_usize!(usize, test_integer_usize); impl_integer_for_usize!(usize, test_integer_usize);
#[test]
fn test_lcm_overflow() {
macro_rules! check {
($t:ty, $x:expr, $y:expr, $r:expr) => { {
let x: $t = $x;
let y: $t = $y;
let o = x.checked_mul(y);
assert!(o.is_none(),
"sanity checking that {} input {} * {} overflows",
stringify!($t), x, y);
assert_eq!(x.lcm(&y), $r);
assert_eq!(y.lcm(&x), $r);
} }
}
// Original bug (Issue #166)
check!(i64, 46656000000000000, 600, 46656000000000000);
check!(i8, 0x40, 0x04, 0x40);
check!(u8, 0x80, 0x02, 0x80);
check!(i16, 0x40_00, 0x04, 0x40_00);
check!(u16, 0x80_00, 0x02, 0x80_00);
check!(i32, 0x4000_0000, 0x04, 0x4000_0000);
check!(u32, 0x8000_0000, 0x02, 0x8000_0000);
check!(i64, 0x4000_0000_0000_0000, 0x04, 0x4000_0000_0000_0000);
check!(u64, 0x8000_0000_0000_0000, 0x02, 0x8000_0000_0000_0000);
}