Add fast iterated point doubling #4221
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reneme
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Jul 17, 2024
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| constexpr Self dbl_n(size_t n) const { | ||
| // TODO it is possible to optimize this by carrying over values from | ||
| // the previous iteration into the next | ||
| if constexpr(Self::A_is_minus_3) { |
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In case you want to express this as a good-old function overload, I think you could do this:
constexpr Self dbl_n(size_t n const)
requires(Self::A_is_minus_3)
{
// ...
}
constexpr Self dbl_n(size_t n const)
requires(!Self::A_is_minus_3)
{
// ...
}... to avoid the if constexpr spanning the entirety of the function. No strong opinion on what is more idiomatic from my side. But, I generally think, the less indentation the better.
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I expect in the future this will expand to cover other types of curves (A == 0 and/or generic A) in which case the single function will be cleaner.
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| auto nx = x(); | ||
| auto ny = y(); | ||
| auto nz = z(); | ||
| ny = ny.mul2(); | ||
| auto w = nz.square().square(); |
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Does it make sense to early-return on n == 0?
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Not really in practice - we call this with n derived from window sizes so n is always > 0
Improves ECDH performance for curves with A == -3 by 5-9%
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Improves ECDH performance for curves with A == -3 by 5-9%
#4027