Extremely fast non-cryptographic hash algorithm
C Makefile Groff CMake
Latest commit 7fc5ce8 Jan 5, 2017 @Cyan4973 minor cleaning


xxHash - Extremely fast hash algorithm

xxHash is an Extremely fast Hash algorithm, running at RAM speed limits. It successfully completes the SMHasher test suite which evaluates collision, dispersion and randomness qualities of hash functions. Code is highly portable, and hashes are identical on all platforms (little / big endian).

Branch Status
master Build Status
dev Build Status


The benchmark uses SMHasher speed test, compiled with Visual 2010 on a Windows Seven 32-bits box. The reference system uses a Core 2 Duo @3GHz

Name Speed Quality Author
xxHash 5.4 GB/s 10 Y.C.
MurmurHash 3a 2.7 GB/s 10 Austin Appleby
SBox 1.4 GB/s 9 Bret Mulvey
Lookup3 1.2 GB/s 9 Bob Jenkins
CityHash64 1.05 GB/s 10 Pike & Alakuijala
FNV 0.55 GB/s 5 Fowler, Noll, Vo
CRC32 0.43 GB/s 9
MD5-32 0.33 GB/s 10 Ronald L.Rivest
SHA1-32 0.28 GB/s 10

Q.Score is a measure of quality of the hash function. It depends on successfully passing SMHasher test set. 10 is a perfect score. Algorithms with a score < 5 are not listed on this table.

A new version, XXH64, has been created thanks to Mathias Westerdahl's contribution, which offers superior speed and dispersion for 64-bits systems. Note however that 32-bits applications will still run faster using the 32-bits version.

SMHasher speed test, compiled using GCC 4.8.2, on Linux Mint 64-bits. The reference system uses a Core i5-3340M @2.7GHz

Version Speed on 64-bits Speed on 32-bits
XXH64 13.8 GB/s 1.9 GB/s
XXH32 6.8 GB/s 6.0 GB/s

This project also includes a command line utility, named xxhsum, offering similar features as md5sum, thanks to Takayuki Matsuoka contributions.


The library files xxhash.c and xxhash.h are BSD licensed. The utility xxhsum is GPL licensed.

Build modifiers

The following macros influence xxhash behavior. They are all disabled by default.

  • XXH_FORCE_NATIVE_FORMAT : on big-endian systems : use native number representation, resulting in system-specific results. Breaks consistency with little-endian results.
  • XXH_ACCEPT_NULL_INPUT_POINTER : if presented with a null-pointer, xxhash result is the same as a null-length key, instead of a dereference segfault.
  • XXH_NO_LONG_LONG : removes support for XXH64, useful for targets without 64-bits support.
  • XXH_STATIC_LINKING_ONLY : gives access to state definition for static allocation. Incompatible with dynamic linking, due to risks of ABI changes.
  • XXH_PRIVATE_API : Make all functions static and accessible through xxhash.h for inlining. Do not compile xxhash.c as a separate module in this case.
  • XXH_NAMESPACE : prefix all symbols with the value of XXH_NAMESPACE, in order to evade symbol naming collisions, in case of multiple inclusions of xxHash library (typically via intermediate libraries).

Other languages

Beyond the C reference version, xxHash is also available on many programming languages, thanks to great contributors. They are listed here.

Branch Policy

  • The "master" branch is considered stable, at all times.
  • The "dev" branch is the one where all contributions must be merged before being promoted to master.
    • If you plan to propose a patch, please commit into the "dev" branch, or its own feature branch. Direct commit to "master" are not permitted.