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gh-121562: optimized hex_from_char#121563

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mdickinson merged 4 commits intopython:mainfromLimaBD:hex-from-char-performance
Jul 14, 2024

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@LimaBDLimaBD commentedJul 10, 2024•
edited by bedevere-appbot
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Optimized hex_from_char performance

issue#121562

Timing with old hex_from_char:

$ ./python -m pyperf timeit --duplicate 100 "float.fromhex('0x123456.ffffp10')".....................Mean +- std dev: 86.0 ns +- 0.9 ns

With new hex_from_char:

$ ./python -m pyperf timeit --duplicate 100 "float.fromhex('0x123456.ffffp10')".....................Mean +- std dev: 81.8 ns +- 1.0 ns

If we measurehex_from_char directly, probably we will get a much better % improvement because there is additional calls thatfloat.fromhex makes apart from this one.

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LGTM in principle. The old code is agnostic to character encoding (works equally well with ASCII / EBCDIC / whatever), while the new code is based on the bytes of the UTF8-encoded string. That's fine, since the only use-case is applying this to a UTF-8-encoded value. But please could we add a comment that makes it clear that this table should only be used with encodings whose lower half is ASCII (like UTF-8).

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Hello@mdickinson, thanks for your time, I just added the comment clarifying it but my English is average, anything let me know!

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Thanks for the update; the comment looks good.

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@mdickinsonmdickinson merged commit04130b2 intopython:mainJul 14, 2024
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@LimaBD Merged. Thank you for the contribution!

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@LimaBDLimaBD deleted the hex-from-char-performance branchJuly 14, 2024 12:35
estyxx pushed a commit to estyxx/cpython that referenced this pull requestJul 17, 2024
Performance improvement to `float.fromhex`: use a lookup tablefor computing the hexadecimal value of a character, in place of theprevious switch-case construct. Patch by Bruno Lima.
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