When Compilers Disagree About UTF‑8

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...

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kstenerud 5 days ago | parent | prev [-]

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.

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duskwuff 4 hours ago | parent | next [-]

> 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 4 hours ago \| parent [-]
		That, plus markup, be it something XML/HTML-like or something Markdown-like.

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vlovich123 2 hours ago | parent | prev | next [-]

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.

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zX41ZdbW 3 hours ago | parent | prev [-]

This is one of the optimizations from ClickHouse - detect ASCII and go a fast path: https://github.com/ClickHouse/ClickHouse/blob/6cde32de1a2463...