gh-154566: Fix array.byteswap() corrupting 'Zd' arrays with more than one element - #154567
Merged
Merged
Conversation
…e than one element The 16-byte-item loop in array_array_byteswap_impl() advanced the buffer pointer by only 8 bytes per iteration, even though each iteration swaps a full 16-byte item (two independent 8-byte halves for the real/imaginary double components). This caused every item after the first to overlap the previous iteration's byte window and come out scrambled. A single byteswap() call gave wrong bytes for the second item onward. Calling byteswap() twice happened to round-trip back to the original value (the corruption is self-canceling under double application), which is why the existing test suite -- which only checked a double-call round-trip -- didn't catch it. Added a regression test that checks the actual byte-level result of a single call.
This comment was marked as resolved.
This comment was marked as resolved.
skirpichev
reviewed
Jul 24, 2026
skirpichev
added
the
needs backport to 3.15
Member
I will wait until @PhysicistJohn applies your suggestions before reviewing this change. |
…l test Per skirpichev's review on pythonGH-154567: - Trim the NEWS entry to his suggested wording. - Move test_byteswap_single_call_result from ComplexDoubleTest into the shared CFPTest base class, using self.example and computing itemsize/half dynamically instead of hardcoded values, so it now covers both ComplexFloatTest ('Zf') and ComplexDoubleTest ('Zd') rather than just one.
Contributor
Author
|
Thanks for the review! Applied all three: trimmed the NEWS wording per |
skirpichev
approved these changes
Jul 24, 2026
Member
|
A CI job failed for an unknown reason:
I clicked on [Update branch] to attempt to repair the CI. |
|
Thanks @PhysicistJohn for the PR, and @vstinner for merging it 🌮🎉.. I'm working now to backport this PR to: 3.15. |
|
GH-155756 is a backport of this pull request to the 3.15 branch. |
bedevere-app
Bot
removed
the
needs backport to 3.15
Member
|
Merged, thanks for the fix. |
hugovk
pushed a commit
that referenced
this pull request
Aug 14, 2026
…re than one element (GH-154567) (#155756) gh-154566: Fix array.byteswap() corrupting 'Zd' arrays with more than one element (GH-154567) Fix array.array.byteswap() corrupting data for 'Zd' (complex double) arrays with more than one element: the 16-byte item loop advanced the buffer pointer by only 8 bytes per iteration, causing items after the first to be scrambled. (cherry picked from commit 46c355f) Co-authored-by: PhysicistJohn <54456354+PhysicistJohn@users.noreply.github.com> Co-authored-by: Victor Stinner <vstinner@python.org>
mbeijen
pushed a commit
to mbeijen/cpython
that referenced
this pull request
Aug 14, 2026
…e than one element (python#154567) Fix array.array.byteswap() corrupting data for 'Zd' (complex double) arrays with more than one element: the 16-byte item loop advanced the buffer pointer by only 8 bytes per iteration, causing items after the first to be scrambled. Co-authored-by: Victor Stinner <vstinner@python.org>
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
3 participants
Add this suggestion to a batch that can be applied as a single commit.This suggestion is invalid because no changes were made to the code.Suggestions cannot be applied while the pull request is closed.Suggestions cannot be applied while viewing a subset of changes.Only one suggestion per line can be applied in a batch.Add this suggestion to a batch that can be applied as a single commit.Applying suggestions on deleted lines is not supported.You must change the existing code in this line in order to create a valid suggestion.Outdated suggestions cannot be applied.This suggestion has been applied or marked resolved.Suggestions cannot be applied from pending reviews.Suggestions cannot be applied on multi-line comments.Suggestions cannot be applied while the pull request is queued to merge.Suggestion cannot be applied right now. Please check back later.
array.array('Zd', ...).byteswap()scrambled every item after the firstbecause the 16-byte-item loop advanced the pointer by 8 bytes instead of
16. Fixes gh-154566.
Adds a regression test that checks the actual byte-level result of a
single
byteswap()call (the existing test only checked a double-callround-trip, which passes even under the bug since the corruption happens
to be self-canceling on the second call).