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Merge pull request #65 from cuviper/pow-overflow 

pow: avoid unnecessary overflows
This commit is contained in:
Alex Crichton 2015-03-08 10:50:41 -07:00
parent fbd7d81b44 043a5b2918
commit 65226fdd06
1 changed files with 7 additions and 2 deletions
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9
src/lib.rs
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@ -121,7 +121,8 @@ pub fn abs_sub<T: Signed>(x: T, y: T) -> T {
/// ```rust /// ```rust
/// use num; /// use num;
/// ///
/// assert_eq!(num::pow(2i, 4), 16); /// assert_eq!(num::pow(2i8, 4), 16);
/// assert_eq!(num::pow(6u8, 3), 216);
/// ``` /// ```
#[inline] #[inline]
pub fn pow<T: Clone + One + Mul<T, Output = T>>(mut base: T, mut exp: usize) -> T { pub fn pow<T: Clone + One + Mul<T, Output = T>>(mut base: T, mut exp: usize) -> T {
@ -132,7 +133,11 @@ pub fn pow<T: Clone + One + Mul<T, Output = T>>(mut base: T, mut exp: usize) ->
if (exp & 1) == 1 { if (exp & 1) == 1 {
acc = acc * base.clone(); acc = acc * base.clone();
} }
base = base.clone() * base;
// avoid overflow if we won't need it
if exp > 1 {
base = base.clone() * base;
}
exp = exp >> 1; exp = exp >> 1;
} }
acc acc