Ciao, Il Gio, 22 Agosto 2019 7:24 am, Niels Möller ha scritto: > Seth Troisi <brain...@gmail.com> writes:
>> In order to profile parts of this I also added tune/speed support for >> mpz_nextprime >> Note that I change the behavior of s->size to mean size bits instead >> of limbs for for measuring mpz_nextprime, as the function is slow (in It's not easy to discuss code if the code is elsewhere... can you post it here? I glanced at your proposed code, with mpz_tdiv_r_2exp you make sure that the operand has "at most" s->size bits. I'd add mpz_setbit to make sure that the operand has exactly the given bit-size. > Good. I imagine mpz_nextprime performance has some room for improvement. > > For benchmarking, maybe one should use something other than arithmetic > mean for averaging, since some numbers will be much slower than others? Currently tune/speed usually use the mean of many calls with the same input. Maybe for _nextprime we should use a chain? Give the previous result as the new input. >> For implementing mpz_prevprime, I tried to reuse as much code as > Maybe it would make sense to generalize a bit further, and write a > function to find the first prime (if any) in an arithmetic sequence. > I.e., find the smallest k >= such that A + kB is prime (if any). A Interesting idea. >> Finally for mpz_prevprime(rop, op <= 2) it's not clear what rop should >> be set to, so I use the smallest prime (2). > > I'd prefer using the function return value to indicate success/failure. I know that my proposal is an incompatible change for the interface... but I'd suggest to extend the range for mpz_nextprime. Can we consider both positive and negative primes? Curently, mpz_nextprime returns 2 for negative inputs. What if we extend the function in such a way that _nextprime(-10) returns -7? Then the implementation of _prevprime(n) will be - _nextprime( - n) and _prevprime(2) will coherently be -2 :-) Ĝis, m -- http://bodrato.it/papers/ _______________________________________________ gmp-devel mailing list gmp-devel@gmplib.org https://gmplib.org/mailman/listinfo/gmp-devel
