Dear Roberto,
Date: Wed, 28 Jan 2009 13:55:06 +0100 From: Roberto Bagnara bagnara@cs.unipr.it
Jim White wrote:
I have a loop that spends 99+% of its time executing these two statements:
mpz_addmul_ui(BB, B, a); mpz_swap (B, BB);To my surprise, it runs 25% faster if I replace it with:
if (a==1) mpz_add (BB, B, BB); else mpz_addmul_ui(BB, B, a); mpz_swap(B, BB);It's an RCF (regular continued-fraction) algorithm, so a=1 about 41.5% of the time.
No big deal, but perhaps in future revs mpz_addmul_ui and its sister function might auto-detect this case and reroute the call?
In the Parma Polyhedra Library, we found out that, for mpz_mul(), checking the source arguments against 0 gives rise to significant speedups in some algorithms.
this surprises me, since 0 has a special representation in mpz, and thus is early detected in mpz_add and mpz_mul. Please can you give an example?
For an unsigned int argument (the 3rd argument 'a' above in mpz_addmul_ui) there is no special treatement for 0 (or 1) if I remember correctly, so it is indeed the responsibility of the user to check that case.
Paul Zimmermann