AI tool finds an O(n²) edge case in Roaring bitmap unions

lemire · x · 2026-07-24

Daniel Lemire says AI tool @perfloop found a degenerate case in mainstream Roaring bitmap implementations: unioning many containers can turn the key-union step into an O(n²) routine. He patched the issue in C/C++, Go, and Java, and notes the slowdown is usually not dominant in practice but remains avoidable.

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