Ciao Niels,
17 feb 2024, 17:53 da ni...@lysator.liu.se:
> Niels Möller <ni...@lysator.liu.se> writes:
> The documented conditions say that gmp should return the same cofactors
>
The documentation also says "If abs(a) = abs(b), then s = 0, t = sgn(b)."
>
> canonicalization logic at the end wasn't right. Appending a patch with a
> fix + stricter tests.
>
And if I correctly patched and tested your proposed code. with equal numbers I
get t=0, instead of s=0.
> Without the fix, we could make the wrong choice in case
>
> |s'| = |s| = |b| / 2g
>
> Since it's a bit subtle, it would be nice with a review of this code
> before I commit it.
>
Shat about simply changing the test from > to >= ?
/* Arrange so that |s| < |u| / 2g */
mpz_add (s1, s0, s1);
- if (mpz_cmpabs (s0, s1) > 0)
+ if (mpz_cmpabs (s0, s1) >= 0)
{
mpz_swap (s0, s1);
mpz_sub (t0, t0, t1);
Ĝis,
m
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