Pcurves fixes and additions #4142
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randombit
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If multiscalar multiplication produces the point at infinity, return nullopt Reject a zero scalar Fix is_even Expose wide reduction to library users
reneme
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Jul 2, 2024
| @@ -120,7 +120,7 @@ class IntMod final { | |||
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| constexpr CT::Choice is_even() const { | |||
| auto v = Rep::from_rep(m_val); | |||
| return CT::Choice::from_int(v[0] & 0x01); | |||
| return CT::Choice::from_int(0x01 ^ (v[0] & 0x01)); | |||
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@randombit Isn't the value barrier coming too late, here? I feel like the compiler might come up with branches while calculating 0x01 ^ (v[0] & 0x01), no?
Sorry for digging up this merged pull request.
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Mmm yeah maybe better as ~CT::Choice::from_int(v[0] & 0x01) to remove the temptation.
I'm largely relying on valgrind to warn us if Clang does transformations like that, but of course this only provides assurance for that one particular version of Clang.
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