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CityHash

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This is an old revision of this page, as edited by Royanee (talk | contribs) at 19:58, 6 February 2017 (Cite source for FarmHash announcement.). The present address (URL) is a permanent link to this revision, which may differ significantly from the current revision.

CityHash is a family of non-cryptographic hash functions, designed for fast hashing of strings. It has 32-, 64-, 128-, and 256-bit variants. CityHash been referenced widely in academic papers.

Google developed the algorithm in-house starting in 2010.[1] The C++ source code for the reference implementation of the algorithm was released in 2011 under an MIT license, with credit to Geoff Pike and Jyrki Alakuijala.[2] The authors expect the algorithm to outperform previous work by a factor of 1.05 to 2.5, depending on the CPU and mix of string lengths being hashed.[3] CityHash is influenced by and partly based on MurmurHash.[4]

Some particularly fast CityHash functions depend on CRC32 instructions that are present in SSE4.2. However, most CityHash functions are designed to be portable, though they will run best on little-endian 32-bit or 64-bit CPUs.[3]

Google has announced FarmHash as the successor to CityHash.[5]

Concerns

CityHash releases do not maintain backward compatibility with previous versions.[6] Users should not use CityHash for persistent storage, or else not upgrade CityHash.

The README warns that CityHash has not been tested much on big-endian platforms.[3]

References

  1. ^ https://code.google.com/p/cityhash/
  2. ^ http://google-opensource.blogspot.com/2011/04/introducing-cityhash.html
  3. ^ a b c https://github.com/google/cityhash/blob/master/README
  4. ^ https://github.com/google/cityhash/blob/master/src/city.cc
  5. ^ https://opensource.googleblog.com/2014/03/introducing-farmhash.html
  6. ^ https://github.com/google/cityhash/blob/master/NEWS
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