Avoid UBSan report in arrayElement#19347
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alexey-milovidov merged 4 commits intomasterfrom Jan 21, 2021
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| else if (index.getType() == Field::Types::Int64) | ||
| { | ||
| /// Cast to UInt64 before negation allows to avoid undefined behaviour for negation of the most negative number. | ||
| /// NOTE: this would be undefined behaviour in C++ sense, but nevertheless, compiler cannot see it on user provided data, |
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AFAIK, it's never an undefined behaviour according to the standard. Conversion from negative signed to unsigned integer is defined as addition of 2^{N-1} and negation of unsigned integer value is defined as 2^N - value. Am I missing something?
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It is the comment explaining why do we have this code (this code prevents UB that will be otherwise possible).
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Changelog entry (a user-readable short description of the changes that goes to CHANGELOG.md):
Avoid UBSan reports in
arrayElementfunction,substringandarraySum. Fixes #19305. Fixes #19287. This closes #19336.