Add Field::sum_of_products method
#80
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str4d
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| /// above. Implementations of `Field` should override this to use more efficient | ||
| /// methods that take advantage of their internal representation, such as interleaving | ||
| /// or sharing modular reductions. | ||
| fn sum_of_products<'a, I: IntoIterator<Item = (&'a Self, &'a Self)> + Clone>(pairs: I) -> Self { |
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I originally made this an iterator of &(a, b), and I tested this against the array impl and saw little-to-no performance difference. I then changed it to an iterator of (&a, &b) because I thought it would be more flexible, but doing that significantly hurts performance (I presume because we're calling .clone() on an owned tuple that contains references, rather than on a reference).
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Yeah, even using nicer tricks for constructing the input arrays, having this API take (&a, &b) causes bls12_381 pairings to be over 5% slower compared to arrays or &(a, b).
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Tried two iterators instead:
fn sum_of_products<'a>(
a: impl IntoIterator<Item = &'a Self> + Clone,
b: impl IntoIterator<Item = &'a Self> + Clone,
) -> Self
and then a.clone().into_iter().zip(b.clone().into_iter()); this is similarly slower than arrays.
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Closes #79.