When Compilers Disagree About UTF‑8
nemanjatrifunovic.substack.comYou 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.
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.
> 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.
That, plus markup, be it something XML/HTML-like or something Markdown-like.
This is one of the optimizations from ClickHouse - detect ASCII and go a fast path: https://github.com/ClickHouse/ClickHouse/blob/6cde32de1a2463...