primeorder: use PrimeField::NUM_BITS to bound the scalar size during point-scalar multiplication
#1119
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…point-scalar multiplication
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Actually, this should speed up some regular curves too, e.g. |
tarcieri
approved these changes
Feb 8, 2025
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Sidebar: seems like we could also add a |
fjarri
commented
Feb 8, 2025
| @@ -122,7 +122,7 @@ where | |||
| } | |||
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| let mut q = Self::IDENTITY; | |||
| let mut pos = C::Uint::BITS as usize - 4; | |||
| let mut pos = (<Scalar<C> as PrimeField>::NUM_BITS.div_ceil(8) * 8) as usize - 4; | |||
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Actually, now that I think about it, .div_ceil(4) * 4 would be more accurate, since we need an integer number of window sizes, not bytes.
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Maybe extract a function for calculating this? It could also be used by a hypothetical mul_vartime
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This probably won't affect actual curves much, but it is useful for test curves which have a small order, but the representation size still has to be large. See also RustCrypto/formats#1649