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deepmind.google·6d ago
AI Engineering
Hacker News·Jun 26·5 min read
A C++ implementation of a fast hash map and hash set using hopscotch hashing
TL;DR
Hash maps and sets often struggle with performance due to collision resolution. The hopscotch-map library offers a C++ implementation using hopscotch hashing, which is faster and more memory-efficient than std::unordered_map.
✦ Why It Matters
Engineers can leverage the hopscotch-map library for improved performance in hash-based data structures.
Key Takeaways
- Use hopscotch-map for faster hash map and set operations.
- Choose prime growth policy for poor hash function scenarios.
- Utilize LessThanComparable keys for better performance with bhopscotch classes.
- Expect improved memory efficiency compared to std::unordered_map.
Full Summary
Hash maps and sets are essential data structures in programming, but they can suffer from performance issues, especially when handling collisions. The hopscotch-map library is a C++ implementation that utilizes hopscotch hashing, a technique that resolves collisions through open-addressing, making it more cache-friendly.
It includes several classes, such as tsl::hopscotch_map and tsl::hopscotch_set, which generally outperform std::unordered_map and are similar to google::dense_hash_map but with lower memory usage. Additionally, the library offers prime growth policy versions for better handling of poor hash functions.
For specific cases, the tsl::bhopscotch_map and tsl::bhopscotch_set provide improved asymptotic performance but require keys to be LessThanComparable. Overall, this library enhances the efficiency of hash-based data structures, making it a valuable tool for developers.