burntsushi

How are you doing a date/time library without platform dependencies like libc or windows-sys? Are you rolling your own bindings in order to get the local time zone? (Or perhaps you aren't doing that at all.)

Ah gotya, thanks!

Disclosure: I'm the author of the memchr crate.

You mention the memchr crate, but you don't seem to have benchmarked it. Instead, you benchmarked the needle crate (last updated 7 years ago). Can you explain a bit more about your methodology?

The memchr crate in particular doesn't just use Rabin-Karp. It also uses Two-Way. And SIMD (with support for x86-64, aarch64 and wasm32).

Both Perl and Python use backtracking regex engines and are thus susceptible to similar problems as discussed in the OP.

Cross-posting from reddit:

The PR has more details, but here are a few ad hoc benchmarks using ripgrep on my M2 mac mini while searching a 5.5GB file.

This one is just a case insensitive search. A case insensitive regex expands to something like (ignoring Unicode) [Ss][Hh][Ee][Rr]..., which means that it has multiple literal prefixes. In fact, you can enumerate them! As long as the set is small enough, this is something that the new SIMD acceleration on aarch64 can handle (and has done for a long time on x86-64):

$ time rg-before-teddy-aarch64 -i -c 'Sherlock Holmes' OpenSubtitles2018.half.en
3055

real    8.208
user    7.731
sys     0.467
maxmem  5600 MB
faults  191

$ time rg-after-teddy-aarch64 -i -c 'Sherlock Holmes' OpenSubtitles2018.half.en
3055

real    1.137
user    0.695
sys     0.430
maxmem  5904 MB
faults  203

And of course, using multiple literals explicitly also uses this optimization:

$ time rg-before-teddy-aarch64 -c 'Sherlock Holmes|John Watson|Irene Adler|Inspector Lestrade|Professor Moriarty' OpenSubtitles2018.half.en
3804

real    9.055
user    8.580
sys     0.474
maxmem  4912 MB
faults  11

$ time rg-after-teddy-aarch64 -c 'Sherlock Holmes|John Watson|Irene Adler|Inspector Lestrade|Professor Moriarty' OpenSubtitles2018.half.en
3804

real    1.121
user    0.697
sys     0.422
maxmem  4832 MB
faults  11

And it doesn't just work for prefixes, it also works for inner literals too:

$ time rg-before-teddy-aarch64 -c '\w+\s+(Sherlock Holmes|John Watson|Irene Adler|Inspector Lestrade|Professor Moriarty)\s+\w+' OpenSubtitles2018.half.en
773

real    9.065
user    8.586
sys     0.477
maxmem  6384 MB
faults  11

$ time rg-after-teddy-aarch64 -c '\w+\s+(Sherlock Holmes|John Watson|Irene Adler|Inspector Lestrade|Professor Moriarty)\s+\w+' OpenSubtitles2018.half.en

773

real    1.124
user    0.702
sys     0.421
maxmem  6784 MB
faults  11

If you're curious about how the SIMD stuff works, you can read my description of Teddy here. I ported this algorithm out of the Hyperscan project several years ago, and it has been one of the killer ingredients for making ripgrep fast in a lot of common cases. But it only worked on x86-64. With the rise and popularity of aarch64 and Apple silicon, I was motivated to port it over. I just recently finished analogous work for the memchr crate as well.

Shortly after we resigned, the top-level team leads, project directors to the Foundation, core team members and the new mods got together to form an interim leadership cohort. Sometimes called the "leadership chat." That then evolved into the Leadership Council by way of an RFC on goverance.