|No such thing as a small change|
Re^2: Why is this code so much slower than the same algorithm in C?by wanna_code_perl (Monk)
|on Dec 09, 2008 at 04:04 UTC||Need Help??|
Thanks for the comments. Here are a few more results, based on your suggestions and comments:
Yes, I acknowledged in the original post that the C algorithm is actually a bit less efficient. Putting the missing comparison into the Perl version instead of the loop label, as you have done, actually had no measurable effect on runtime.
Moving my ($i, j) outside the loop had no measurable effect on runtime. Also not too surprising.
Running your version exactly as listed took on average 48.8 +/- 0.1 sec—again no measurable change from my previous results.
True, I could use more rigorous methods to more accurately measure the effect of the above changes, but at best we'd be looking at a fraction of a percentage difference. Nowhere near the 3000+ % difference in the C version.
Adding use integer; to your version caused it to run in 46.8 sec, which is a marginal improvement. (My test machine has an FPU).
Not forgetting my original question of why this runs so slow, your optimization ideas do help shed a little light on a few of the factors that may be influencing performance.
It's perhaps important to underscore that my question is not, "what can I do to speed up this random little demonstration program", but instead, "why is Perl so much slower than C on some arbitrary, computationally expensive algorithm". Perhaps more to the point, "what are the factors influencing the performance of tight loops in Perl". (Or where could I read more about that topic!)
Hope that makes a bit more sense. Thanks again for your insights!