Fast open addressing hash table in C++.
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::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.
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
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Copyright (c) 2020 Michael Clark <email@example.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. THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.