fix: Further improve performance of the UTF-8 string comparison logic #2182
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The semantics of this logic were originally fixed by #1967, but this fix caused a material performance degradation, which was then improved by #2021. The performance was, however, still suboptimal, and this PR further improves the speed back to close to its original speed and, serendipitously, simplifies the algorithm too. This commit effectively ports the following two PRs from the firebase-android-sdk repository: - firebase/firebase-android-sdk#7098 - firebase/firebase-android-sdk#7109
dconeybe
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wu-hui
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Jul 7, 2025
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This PR both improves performance and simplifies the UTF-8 string comparison logic. It addresses prior performance regressions by introducing a more optimized algorithm for string ordering.
The semantics of the UTF-8 string comparison logic were originally fixed by #1967, but this fix caused a material performance degradation, which was then improved by #2021. The performance was, however, presumably still sub-optimal, and this PR further improves the speed back to close to its original speed and, serendipitously, simplifies the algorithm too.
This PR effectively ports the following two PRs from the firebase-android-sdk repository:
Highlights
compareUtf8Strings()method inOrder.javahas been rewritten to improve performance and simplify its logic. The new algorithm leverages the relationship between UTF-8 and UTF-16 representations for more efficient string comparison, avoiding costly byte string conversions.codePointAtandByteString.copyFromUtf8for non-ASCII characters has been replaced with a more straightforward character-by-character comparison that intelligently handles surrogate pairs.OrderTest.javahas been updated to improve the robustness of thecompareUtf8Strings()test. Instead of asserting exact return values, it now checks thesignum(sign) of the comparison result, which is a more appropriate way to validate comparator behavior.