A C++ implementation of a fast hash map and hash set using hopscotch hashing

Post by nly » Sat, Jun 27, 2026, 10:17 PM UTC

spacechild1 wrote: post #20

nly wrote: post #15

My goto these days (and afaik the state of the art) is boost::unordered_flat_set paired with rapidhash for hashing (since the GNU std::hash functions based on murmurhash are ridiculously slow) The cacheline performance is pretty hard to beat (SIMD optimised linear scan before hopping), which is where all the wins come in the real world. But basically any of the faster hash maps from absl, boost or folly are going to…

> with rapidhash for hashing (since the GNU std::hash functions based on murmurhash are ridiculously slow) Doesn't boost::unordered_flat_map use boost::hash by default? How does it compare to rapid hash and std::hash?

Post by AlexeyBelov » Sun, Jun 28, 2026, 6:23 AM UTC

stevefan1999 wrote: post #18

Ah, hopscotch hash, I tried using it on my CSGO cheat literally 10 years ago, for the object reflection (retrospection) system based on compiler type ID and unique hashing scheme with function signature. I merely used it for hopefully getting a performance on the "dependency injection" side of things, until I realized it is actually a service locator pattern and performance won't improve due to this architecture anyw…

Post by lefty2 » Mon, Jun 29, 2026, 9:18 AM UTC

nly wrote: post #15

My goto these days (and afaik the state of the art) is boost::unordered_flat_set paired with rapidhash for hashing (since the GNU std::hash functions based on murmurhash are ridiculously slow) The cacheline performance is pretty hard to beat (SIMD optimised linear scan before hopping), which is where all the wins come in the real world. But basically any of the faster hash maps from absl, boost or folly are going to…