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Replace manual implementation with carrying_mul_add #147666

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Merged
merged 1 commit into from
Oct 15, 2025
+2 −3
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Replace manual implementation with carrying_mul_add #147666

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5 changes: 2 additions & 3 deletions library/core/src/num/bignum.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -38,9 +38,8 @@ macro_rules! impl_full_ops {
fn full_mul_add(self, other: $ty, other2: $ty, carry: $ty) -> ($ty, $ty) {
// This cannot overflow;
// the output is between `0` and `2^nbits * (2^nbits - 1)`.
let v = (self as $bigty) * (other as $bigty) + (other2 as $bigty) +
(carry as $bigty);
((v >> <$ty>::BITS) as $ty, v as $ty)
let (lo, hi) = self.carrying_mul_add(other, other2, carry);
(hi, lo)
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Oh, interesting that this method had picked the opposite order. I guess we were all taught math in big-endian, even if it's kinda worse 🙃

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Yeah, it was not obvious at first, so it took some time to understand why tests are not passing

}

fn full_div_rem(self, other: $ty, borrow: $ty) -> ($ty, $ty) {
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