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v0.5.1
https://github.com/python/cpython
09 December 2020, 11:06:31 UTC
Revision c1bbca5b004b3f74d240ef8a76ff445cc1a27efb authored by Miss Islington (bot) on 21 November 2020, 09:18:41 UTC, committed by GitHub on 21 November 2020, 09:18:41 UTC 
bpo-40791: Make compare_digest more constant-time. (GH-20444)
 

* bpo-40791: Make compare_digest more constant-time.

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>
1 parent ed02018
History
Tip revision: c1bbca5b004b3f74d240ef8a76ff445cc1a27efb authored by Miss Islington (bot) on 21 November 2020, 09:18:41 UTC
bpo-40791: Make compare_digest more constant-time. (GH-20444)
Tip revision: c1bbca5
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