zhashmap

Fast open addressing hash table in C++.

Overview

This hashmap is an open-addressing hashtable similar to google/dense_hash_map, however, it uses tombstone bitmaps to eliminate necessity for empty or deleted key sentinels. This means the hash map could potentially be made into a drop-in replacement for std::map or std::unordered_map. The code supports enough of the C++ unordered associative container requirements such that it can be substituted for many typical use-cases.

These small maps are useful for histograms and other frequently accessed data structures where performance is critical.

Benchmarks

The following benchmarks were performed on an Intel Core i9-7980XE using GCC 9.2. Note this benchmark is somewhat contrived, but is intended to measure minimum latency for small histogram hashtables.

update 10M mod 16383 records

License

This software is released under the ISC license:

Copyright (c) 2020 Michael Clark <michaeljclark@mac.com>

Permission to use, copy, modify, and distribute this software for any
purpose with or without fee is hereby granted, provided that the above
copyright notice and this permission notice appear in all copies.

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WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
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