perf: improve utf_char2cells() performance #27353
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zeertzjq
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You may also want to take #18690 into consideration. |
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Should I make characters above 10FFFF unprintable? |
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Hmm, actually it's not hard to add that check later, so not really necessary. |
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Thanks so much everyone! |
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`utf_char2cells()` calls `utf_printable()` twice (sometimes indirectly, through `vim_isprintc()`) for characters >= 128. The function can be refactored to call to it only once. `utf_printable()` uses binary search on ranges of unprintable characters to determine if a given character is printable. Since there are only 9 ranges, and the first range contains only one character, binary search can be replaced with SSE2 SIMD comparisons that check 8 ranges at a time, and the first range is checked separately. SSE2 is enabled by default in GCC, Clang and MSVC for x86-64. Add 3-byte utf-8 to screenpos_spec benchmarks.
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utf_char2cells()callsutf_printable()twice (sometimes indirectly, throughvim_isprintc()) for characters >= 128. The function can be refactored to call to it only once.utf_printable()uses binary search on ranges of unprintable characters to determine if a given character is printable. Since there are only 9 ranges, and the first range contains only one character, binary search can be replaced with SSE2 SIMD comparisons that check 8 ranges at a time, and the first range is checked separately.SSE2 is enabled by default in GCC, Clang and MSVC for x86-64.
I tested the function and it returns the same results for all 2^32 values.
Benchmarks:
I modified the benchmarks from #26813 to better reflect the performance difference and added a new benchmark that measures 3 byte utf-8 separately.