Guido Vranken <guidovran...@gmail.com> writes: > Computing extended gcd using mpz_gcdext where a = 1, b = 2: > > libgmp: g: 1, s: 1, t: 0 > mini-gmp: g: 1, s: -1, t: 1 > This violates the docs: "s = sgn(a) if abs(b) = 2", e.g. s must be 1 > > Computing extended gcd using mpz_gcdext where a = 6, b = 4: > libgmp: g: 2, s: 1, t: -1 > mini-libgmp: g: 2, s: -1, t: 2
I think mini-gmp is wrong here, I'll have to investigate. Thanks for reporting. > The docs state: "abs(s) < abs(b) / (2 g) and abs(t) < abs(a) / (2 g)" > I think that should be: "abs(s) <= abs(b) / (2 g) and abs(t) <= abs(a) / (2 > g)" > (< should be <=) These strict equalities don't hold for the documented "exceptional" cases. IT seems both your examples have abs(B) = 2G, so that's the case that applies. It is a bit subtle. And even if one relaxes the inequalities as you suggest, 1 = gcd(1,1) would still be an exception (since in that case, we'd get |s|, |t| < 1/2, i.e., s = t = 0, which isn't reasonable). Can you suggest any doc change to make it clearer? Regards, /Niels -- Niels Möller. PGP key CB4962D070D77D7FCB8BA36271D8F1FF368C6677. Internet email is subject to wholesale government surveillance. _______________________________________________ gmp-bugs mailing list gmp-bugs@gmplib.org https://gmplib.org/mailman/listinfo/gmp-bugs
