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⚡ Optimize O(N^2) vector erase loop in ISO Demuxer chunk validation #281

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⚡ Optimize O(N^2) vector erase loop in ISO Demuxer chunk validation #281

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20 changes: 12 additions & 8 deletions src/demuxer/iso/ErrorRecovery.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -199,14 +199,18 @@ bool ErrorRecovery::RepairSampleToChunkTable(SampleTableInfo& tables) {
}

// Check for invalid entries in sample-to-chunk table
for (auto it = tables.sampleToChunkEntries.begin(); it != tables.sampleToChunkEntries.end(); ) {
if (it->samplesPerChunk == 0 || it->sampleDescIndex == 0) {
// Invalid entry, remove it
it = tables.sampleToChunkEntries.erase(it);
LogError("ChunkTableRepair", "Removed invalid sample-to-chunk entry");
} else {
++it;
}
size_t originalSize = tables.sampleToChunkEntries.size();
tables.sampleToChunkEntries.erase(
std::remove_if(tables.sampleToChunkEntries.begin(), tables.sampleToChunkEntries.end(),
[](const auto& entry) {
return entry.samplesPerChunk == 0 || entry.sampleDescIndex == 0;
}),
tables.sampleToChunkEntries.end()
);

size_t removedCount = originalSize - tables.sampleToChunkEntries.size();
for (size_t i = 0; i < removedCount; ++i) {
LogError("ChunkTableRepair", "Removed invalid sample-to-chunk entry");
}
Comment on lines +212 to 214
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@gemini-code-assist gemini-code-assist Bot Apr 8, 2026

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medium

While this loop accurately duplicates the original logging behavior as noted in the PR description, calling LogError $N$ times introduces a significant $O(N)$ overhead due to the std::map lookup and string handling inside LogError. For large datasets (e.g., the $N=50,000$ case mentioned in the benchmarks), this overhead will likely dominate the execution time, negating much of the performance gain achieved by the std::remove_if optimization. Unless individual log entries are strictly required for each removed item, consider logging a single summary message and updating the statistics in bulk.

    if (removedCount > 0) {
        LogError("ChunkTableRepair", "Removed " + std::to_string(removedCount) + " invalid sample-to-chunk entries");
        if (removedCount > 1) {
            errorStats["ChunkTableRepair"] += static_cast<int>(removedCount - 1);
        }
    }


// If all entries were invalid, create a default entry
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Empty file modified util/build-deps.sh
100644 → 100755
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