py/objint_longlong: Fix left shift of negative values. #17734
+25
−5
Conversation
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
|
Hmm, so running the (I don't see these locally, but I have a different gcc locally.) This looks a lot like the problem @koxudaxi was describing in #17649... |
Codecov ReportAll modified and coverable lines are covered by tests ✅
Additional details and impacted files@@ Coverage Diff @@
## master #17734 +/- ##
=======================================
Coverage 98.41% 98.41%
=======================================
Files 171 171
Lines 22210 22210
=======================================
Hits 21857 21857
Misses 353 353 ☔ View full report in Codecov by Sentry. 🚀 New features to boost your workflow:
|
|
Code size report: |
Previous comment was wrong, left shifting a negative value is UB in C. Use the same approach as small int shifts (from runtime.c). Signed-off-by: Angus Gratton <angus@redyak.com.au>
Skip the tests if MicroPython can't represent >64-bit integers (these tests repeatedly left shift values by 8 bits). It would be possible to have these tests work in this case I think, as the results are always masked to shorter values. But quite fiddly. This work was funded through GitHub Sponsors. Signed-off-by: Angus Gratton <angus@redyak.com.au>
projectgus
force-pushed
the
bugfix/longlong_shift
branch
from
d2517f1 to
09c6e9b
Compare
projectgus
changed the title
|
Have pulled out the CI change to its own PR. |
dpgeorge
reviewed
Jul 22, 2025
| || lhs_val > (LLONG_MAX >> rhs_val) | ||
| || lhs_val < (LLONG_MIN >> rhs_val); | ||
| if (!overflow) { | ||
| result = (unsigned long long)lhs_val << rhs_val; |
There was a problem hiding this comment.
Does this need a cast to unsigned? lhs_val can still be negative here, but that should be OK.
dpgeorge
reviewed
Jul 22, 2025
| int("0x10000000000000000", 16) | ||
| except: | ||
| print("SKIP") # No support for >64-bit integers | ||
| raise SystemExit |
There was a problem hiding this comment.
Instead of this, could rename the test to end with _intbig.py. Eg following tests/micropython/viper_misc_intbig.py and tests/micropython/viper_const_intbig.py etc.
|
Another option to fix the overflow check would be: if ((int)rhs_val > 62) {
overflow = 1;
} else {
rhs_val = 1ll << (int)rhs_val;
overflow = mp_mul_ll_overflow(lhs_val, rhs_val, &result);
}I am not sure which one would generate the shortest code, given that the compiler might be able to merge the call to |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
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.
Summary
Closes #17702, thanks to @jepler for running these additional checks.
Note: First version of this PR enabled UBSan for longlong tests, but this surfaced another issue so has been spun out to #17735.
Testing
Trade-offs and Alternatives