Re^2: Why is this code so much slower than the same algorithm in C?

[wanna_code_perl]

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!

[tye]

Because the C code and the Perl code end up doing roughly equivalent things except that the C code runs through a few dozen machine-language instructions while the Perl code runs through a few dozen "opnodes". Machine-language instructions are the fastest unit of execution on a computer. While the slowness of opnode dispatch (each requires several dozen or even hundreds of machine-language instructions) is one of the motivations for some of the design changes in Perl 6.