Roberto Bagnara bagnara@cs.unipr.it writes:
We thought (but we are not sure) that this is indeed a feature, and not a limitation: since only the client code can know about the frequence of special cases, let the client code take the decision. The alternative would be that GMP does a lot of checks that are possibly useless, perhaps duplicating work that has already been done by the client code.
It is indeed very hard for GMP to know, and mpz_addmul_ui could perhaps also check for the arguments 16, 1023, and whatnot. Countless special values could give speedup when actually used, but testing for such values would slow most GMP usages down. And probably introduce hard-to-test-for bugs.
Adding test for special cases to application code is also not a perfect solution, since what values to test for varies from GMP version to GMP version and from hardware to hardware.
Vincent Lefevre vincent@vinc17.org writes:
Is GMP's policy documented somewhere? If not, I think this should be documented, so that the user does not have to do useless checks if they are done by GMP.
I have meant to write a "GMP cookbook" with advice like this.