mpz_prevprime

[Marco Bodrato]

Ciao,

Il 2020-10-16 09:51 Seth Troisi ha scritto:
> won't this cause m = 2*prime, instead of the original result, m = 0?
> I used m = (diff > 0 && m) ? prime - m : m;
> to make sure that p can be marked as composite.

Oops, you are right!

I fear that the short-circuit evaluation of && can force the compiler to 
branch...
(diff > 0) & (m != 0) should be computed branchless...
But that's a stupid detail, as you said most of the time is used in the 
mod function or in millerrabin :-)

Ĝis,
m