[tom_mellior]

If you are using a current version of your C compiler and can consistently reproduce those numbers just by adding something like -O3, you should probably file a bug report. Optimizers can go wrong and sometimes pessimize things a bit, but an almost 50% slowdown from enabling optimizations would be treated as an important bug to fix. (Though people are saying that significant amounts of time in the benchmark are spent in random number generation and output, so maybe try to find out first if the problem lies in one of those.)

[tom_mellior]

Ah, nevermind, (a) even the "non-optimized" C version uses -O3, and (b) the "C" and the "optimized C" programs differ not only in compiler flags but they are actually different source codes. Specifically, the "optimized C" version doesn't use the faster random number generator.

If you fix that, on my machine it's 17.3 seconds for the base C version and 13.4 for the optimized one, i.e., a 22% improvement from turning on the extra optimizations (-march=native and -ffast-math).

And for whatever it's worth, because some people love hating on GCC in favor of Clang, my Clang timings are 19.5 and 16.5 seconds, respectively.