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| author | Miss Islington (bot) <31488909+miss-islington@users.noreply.github.com> | 2020-12-14 17:04:57 (GMT) |
|---|---|---|
| committer | GitHub <noreply@github.com> | 2020-12-14 17:04:57 (GMT) |
| commit | 8bef9ebb1b88cfa4b2a38b93fe4ea22015d8254a (patch) | |
| tree | 83c849580c4e39cd05110f1efb2dab7ac79c0579 /Lib/pydoc_data/topics.py | |
| parent | dae5d728bc3f1d4039b64e4ec3a9036fd5d19587 (diff) | |
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bpo-40791: Make compare_digest more constant-time. (GH-23438) (GH-23767)
The existing volatile `left`/`right` pointers guarantee that the reads will all occur, but does not guarantee that they will be _used_. So a compiler can still short-circuit the loop, saving e.g. the overhead of doing the xors and especially the overhead of the data dependency between `result` and the reads. That would change performance depending on where the first unequal byte occurs. This change removes that optimization.
(This is change GH-1 from https://bugs.python.org/issue40791 .)
(cherry picked from commit 31729366e2bc09632e78f3896dbce0ae64914f28)
Co-authored-by: Devin Jeanpierre <jeanpierreda@google.com>
Diffstat (limited to 'Lib/pydoc_data/topics.py')
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