3 ms·

Thanks for that analysis, very informative! I have not tried to get the best possible performance: at first I wanted to see if it would work at all, and the fa

by fanf2 2y ago

Thanks for that analysis, very informative! I have not tried to get the best possible performance: at first I wanted to see if it would work at all, and the fact that my first attempt performed really well was a bonus! My main point of interest is strings less than the size of a vector register, and getting rid of the troughs in the throughput chart. You can click through the link to the code at the end of the blog post, which has all the licence details. It is 0BSD or MIT-0 except for the parts written originally for BIND which are MPL-2.0.

neonsunset 2y ago
Just to clarify - this was about SWAR version as my interest, similar to what you mentioned in a sibling comment, is in mainly below-vector-width strings, because these are most frequently passed to these kinds of functions by developers. I was going to try to see if it can further "amortize" the jump table with fallthrough for variable lengths below 16 in my C# UTF-8 string implementation that is going to use it. In any case, thanks for writing the article, for some reason there is quite a bit of negativity among users and developers towards AVX512 - it is seen as "AVX2 but twice as wide", which it of course isn't, but most do not know that. Also, you may want to simply do the overlapping conversion for the tail instead of masking out the elements, which is usually faster on the benchmarks (at least give it a try), and also align the source and destination for the loop to avoid split loads/stores.