CityHash

This article is about the family of hash functions. For the running club, see Hash House Harriers.

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.

Concerns

CityHash releases do not maintain backward compatibility with previous versions.[5] 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. 1 2 3 https://code.google.com/p/cityhash/source/browse/trunk/README
  4. ↑ https://code.google.com/p/cityhash/source/browse/trunk/src/city.cc
  5. ↑ https://code.google.com/p/cityhash/source/browse/trunk/NEWS

External links

This article is issued from Wikipedia - version of the Saturday, November 14, 2015. The text is available under the Creative Commons Attribution/Share Alike but additional terms may apply for the media files.