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refactor sub_assign DensePolynomial #906

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refactor sub_assign DensePolynomial #906

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b69e95d
refactor sub_assign DensePolynomial
tcoratger Dec 15, 2024
efcde59
Update poly/src/polynomial/univariate/dense.rs
tcoratger Dec 24, 2024
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34 changes: 15 additions & 19 deletions poly/src/polynomial/univariate/dense.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -509,8 +509,7 @@ impl<'a, F: Field> Sub<&'a SparsePolynomial<F>> for &DensePolynomial<F> {
#[inline]
fn sub(self, other: &'a SparsePolynomial<F>) -> DensePolynomial<F> {
if self.is_zero() {
let result = other.clone();
(-result).into()
(-(other.clone())).into()
} else if other.is_zero() {
self.clone()
} else {
Expand Down Expand Up @@ -538,24 +537,21 @@ impl<'a, F: Field> SubAssign<&'a DensePolynomial<F>> for DensePolynomial<F> {
#[inline]
fn sub_assign(&mut self, other: &'a DensePolynomial<F>) {
if self.is_zero() {
self.coeffs.resize(other.coeffs.len(), F::zero());
} else if other.is_zero() {
return;
} else if self.degree() >= other.degree() {
} else {
// Add the necessary number of zero coefficients.
self.coeffs.resize(other.coeffs.len(), F::zero());
self.coeffs = other.coeffs.iter().map(|&x| -x).collect();
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@Pratyush Pratyush Dec 24, 2024 •
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The hope with the old way was that if self.coeffs has capacity large enough (e.g., it was the result of a previous operation that resulted in a zero), then we can avoid re-allocation via the collect.

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Oh yes you are right didn't notice that. Then there is no point to refactor this, this is already optimized, let us close :)

} else if !other.is_zero() {
if self.degree() < other.degree() {
self.coeffs.resize(other.coeffs.len(), F::zero());
}
self.coeffs
.iter_mut()
.zip(&other.coeffs)
.for_each(|(a, b)| *a -= b);

// If the leading coefficient ends up being zero, pop it off.
// This can happen if they were the same degree, or if other's
// coefficients were constructed with leading zeros.
self.truncate_leading_zeros();
}
self.coeffs
.iter_mut()
.zip(&other.coeffs)
.for_each(|(a, b)| {
*a -= b;
});
// If the leading coefficient ends up being zero, pop it off.
// This can happen if they were the same degree, or if other's
// coefficients were constructed with leading zeros.
self.truncate_leading_zeros();
}
}

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