38 points by rbanffy 4 days ago | 6 comments

MiroslavPokorny
Title is misleading, the compilers do not disagree, running the compiled code produces the same output. The difference is one binary(instructions) are slightly different...
kstenerud
You could actually use SIMD instructions to detect sequences of bytes with the top bit cleared, thus allowing bulk copies of ASCII text without a per-byte loop.
Another optimization would be to take advantage of the fact that codepoint usage tends to cluster around the language of the text. So if you detect usage of 3-byte encodings, chances are you'll continue encountering only 3-byte encodings, with the odd ASCII or emoji codepoints. This opens up even more state machine possibilities.
- duskwuff
  > So if you detect usage of 3-byte encodings, chances are you'll continue encountering only 3-byte encodings, with the odd ASCII or emoji codepoints.
  Depends on what kind of text you're processing. Many languages use the ASCII range for spaces/newlines, digits, and punctuation.
  mort96
  That, plus markup, be it something XML/HTML-like or something Markdown-like.
- vlovich123
  FWIW I believe the second optimization is at odds with the first. It’s really hard to do this kind of conditional historical check in SIMD.
- zX41ZdbW
  This is one of the optimizations from ClickHouse - detect ASCII and go a fast path: https://github.com/ClickHouse/ClickHouse/blob/6cde32de1a2463...