t...@gmplib.org (Torbjörn Granlund) writes: > Checking u1 = 0 and v1 = 0 separately as you suggest is a different > thing, and it might not have zero cost in the gcd_22 loop.
I think only the shifted number should be checked, and as the main loop exit condition. If both u1 > 0 and v1 > 0 on entry (if gcd_22 require that is unclear), then u1 == 0 impliex v1 > 0. > We could do a large rightshift outside the loop and then jump back into > and (ab)use gcd_22 with u1 = 0 xor v1 = 0. I suspect random operands > will not see any timing difference. Don't you agree that u1 / v1 will > not be too far from 1.0 on average? That would probably work fine, but maybe not simpler than an explicit gcd_22. So then the normal case would call gcd_22 with u1 > 0, v1 > 0, and exit the loop with u1 > 0, v1 == 0. I don't see why we'd need a right shift here, I think one could just check if u1 > 0 and if so jump back to gcd_22, and next time the loop exits we will have u1 = 0, v1 = 0. To do the same for the unlikely u0 = 0 exit case, we'd need a large right shift. I think an explicit gcd_21 loop may be clearer, but unlikely to matter for performance. Regards, /Niels -- Niels Möller. PGP-encrypted email is preferred. Keyid 368C6677. Internet email is subject to wholesale government surveillance. _______________________________________________ gmp-devel mailing list gmp-devel@gmplib.org https://gmplib.org/mailman/listinfo/gmp-devel
