On Mon, 29 Nov 2010 13:41:38 +0100 Joerg Sonnenberger <jo...@britannica.bec.de> wrote:
> On Mon, Nov 29, 2010 at 10:44:11AM +0000, Sad Clouds wrote: > > As for calculating the hash, modern hardware has fast modulo > > instructions. A very simple test on Intel Atom D510 processor, seems > > to indicate a single 'interger % prime' is roughly equal to two > > integer operations. > > No, divisions and modulo are still very slow. According the Intel > Architecture Guide, div has a latency of at least 56 cycles compared to > less than 20 cycles for all integer multiplication instructions. > Throughput is at best 1/4 as well. Please check your test case (and the > assembler output) carefully for not hitting the unsigned division > optimisation I mentioned earlier... > > Joerg Yes you are right, modulo is about 4 times slower.
