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Improve pow speed for expensive types by multiplying references not cloned values (reopen) #153

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Improve pow speed for expensive types by multiplying references not cloned values (reopen) #153

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11 changes: 7 additions & 4 deletions traits/src/pow.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -12,21 +12,24 @@ use {One, CheckedMul};
/// assert_eq!(pow(6u8, 3), 216);
/// ```
#[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
where
for<'a> &'a T: Mul<&'a T, Output = T>,
{
if exp == 0 { return T::one() }

while exp & 1 == 0 {
base = base.clone() * base;
base = &base * &base;
exp >>= 1;
}
if exp == 1 { return base }

let mut acc = base.clone();
while exp > 1 {
exp >>= 1;
base = base.clone() * base;
base = &base * &base;
if exp & 1 == 1 {
acc = acc * base.clone();
acc = &acc * &base;
}
}
acc
Expand Down