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Improve performance of rem_euclid() for signed integers #103913

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Merged
merged 3 commits into from
Nov 12, 2022
Merged

Improve performance of rem_euclid() for signed integers #103913

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3ad4d24
Optimize the code to run faster.
Neutron3529 Nov 3, 2022
aafe6db
fix the overflow warning.
Neutron3529 Nov 3, 2022
d81a0e9
update comment
Neutron3529 Nov 4, 2022
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14 changes: 9 additions & 5 deletions library/core/src/num/int_macros.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -2068,11 +2068,15 @@ macro_rules! int_impl {
pub const fn rem_euclid(self, rhs: Self) -> Self {
let r = self % rhs;
if r < 0 {
if rhs < 0 {
r - rhs
} else {
r + rhs
}
// Semantically equivalent to `if rhs < 0 { r - rhs } else { r + rhs }`.
// If `rhs` is not `Self::MIN`, then `r + abs(rhs)` will not overflow
// and is clearly equivalent, because `r` is negative.
// Otherwise, `rhs` is `Self::MIN`, then we have
// `r.wrapping_add(Self::MIN.wrapping_abs())`, which evaluates
// to `r.wrapping_add(Self::MIN)`, which is equivalent to
// `r - Self::MIN`, which is what we wanted (and will not overflow
// for negative `r`).
r.wrapping_add(rhs.wrapping_abs())
} else {
r
}
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