On Mar 12, 2009, at 4:18 PM, William Stein wrote:
>
>> One of the things that drives a lot of my optimizations in Cython has
>> been the maxim that the obvious way should be the fast way, and I
>> especially want to avoid having to resort to tricks to "fool" the
>> compiler to get maximum speed. (Of course in this case we're talking
>> about only a 5% or so difference, assuming no branching). I like the
>
> Are you sure it's a difference of 5%?
>
> I just tried these two programs:
>
> main() {
> int n = -1, m = 16, k, a=0;
> for(k=1;k<100000000;k++) {
> a = n%k + (a<0)?k:0;
> }
> }
>
> and
>
> main() {
> int n = -1, m = 16, k, a=0;
> for(k=1;k<100000000;k++) {
> a = n%k;
> }
> }
>
> and the first takes 22% longer than the second.
Thanks for the timings--5% was a conservative estimate, but I didn't
realize it was that conservative.
- Robert
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