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 | |
dev |
The benchmark uses SMHasher speed test, compiled with Visual 2010 on a Windows Seven 32-bit 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 โ | 9 | |
MD5-32 | 0.33 GB/s | 10 | Ronald L.Rivest |
SHA1-32 | 0.28 GB/s | 10 |
Note โ : SMHasher's CRC32 implementation is known to be slow. Faster implementations exist.
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 more recent version, XXH64, has been created thanks to Mathias Westerdahl, which offers superior speed and dispersion for 64-bit systems. Note however that 32-bit applications will still run faster using the 32-bit version.
SMHasher speed test, compiled using GCC 4.8.2, on Linux Mint 64-bit. The reference system uses a Core i5-3340M @2.7GHz
Version | Speed on 64-bit | Speed on 32-bit |
---|---|---|
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.
You can download and install xxHash using the vcpkg dependency manager:
git clone https://github.com/Microsoft/vcpkg.git
cd vcpkg
./bootstrap-vcpkg.sh
./vcpkg integrate install
./vcpkg install xxhash
The xxHash port in vcpkg is kept up to date by Microsoft team members and community contributors. If the version is out of date, please create an issue or pull request on the vcpkg repository.
The following macros can be set at compilation time, they modify libxxhash behavior. They are all disabled by default.
XXH_INLINE_ALL
: Make all functionsinline
, with bodies directly included withinxxhash.h
. Inlining functions is beneficial for speed on small keys. It's extremely effective when key length is expressed as a compile time constant, with performance improvements observed in the +200% range . See this article for details. Note: there is no need for anxxhash.o
object file in this case.XXH_NO_INLINE_HINTS
: By default, xxHash uses tricks like__attribute__((always_inline))
and__forceinline
to try and improve performance at the cost of code size. Defining this to 1 will mark all internal functions asstatic
, allowing the compiler to decide whether to inline a function or not. This is very useful when optimizing for the smallest binary size, and it is automatically defined when compiling with-O0
,-Os
,-Oz
, or-fno-inline
on GCC and Clang. This may also increase performance depending on the compiler and the architecture.XXH_REROLL
: reduce size of generated code. Impact on performance vary, depending on platform and algorithm.XXH_ACCEPT_NULL_INPUT_POINTER
: if set to1
, when input is aNULL
pointer, xxhash result is the same as a zero-length input (instead of a dereference segfault). Adds one branch at the beginning of the hash.XXH_FORCE_MEMORY_ACCESS
: default method0
uses a portablememcpy()
notation. Method1
uses a gcc-specificpacked
attribute, which can provide better performance for some targets. Method2
forces unaligned reads, which is not standard compliant, but might sometimes be the only way to extract better read performance. Method3
uses a byteshift operation, which is best for old compilers which don't inlinememcpy()
or big-endian systems without a byteswap instructionXXH_CPU_LITTLE_ENDIAN
: by default, endianess is determined at compile time. It's possible to skip auto-detection and force format to little-endian, by setting this macro to 1. Setting it to 0 forces big-endian.XXH_PRIVATE_API
: same impact asXXH_INLINE_ALL
. Name underlines that XXH_* symbols will not be published.XXH_NAMESPACE
: prefix all symbols with the value ofXXH_NAMESPACE
. Useful to evade symbol naming collisions, in case of multiple inclusions of xxHash source code. Client applications can still use regular function name, symbols are automatically translated throughxxhash.h
.XXH_STATIC_LINKING_ONLY
: gives access to state declaration for static allocation. Incompatible with dynamic linking, due to risks of ABI changes.XXH_NO_LONG_LONG
: removes support for XXH64, for targets without 64-bit support.XXH_IMPORT
: MSVC specific : should only be defined for dynamic linking, it prevents linkage errors.
Calling xxhash 64-bit variant from a C program :
#include "xxhash.h"
(...)
XXH64_hash_t hash = XXH64(buffer, size, seed);
}
Using streaming variant is more involved, but makes it possible to provide data incrementally :
#include "stdlib.h" /* abort() */
#include "xxhash.h"
XXH64_hash_t calcul_hash_streaming(FileHandler fh)
{
/* create a hash state */
XXH64_state_t* const state = XXH64_createState();
if (state==NULL) abort();
size_t const bufferSize = SOME_SIZE;
void* const buffer = malloc(bufferSize);
if (buffer==NULL) abort();
/* Initialize state with selected seed */
XXH64_hash_t const seed = 0; /* or any other value */
if (XXH64_reset(state, seed) == XXH_ERROR) abort();
/* Feed the state with input data, any size, any number of times */
(...)
while ( /* any condition */ ) {
size_t const length = get_more_data(buffer, bufferSize, fh);
if (XXH64_update(state, buffer, length) == XXH_ERROR) abort();
(...)
}
(...)
/* Get the hash */
XXH64_hash_t const hash = XXH64_digest(state);
/* State can be re-used; in this example, it is simply freed */
free(buffer);
XXH64_freeState(state);
return hash;
}
Starting with v0.7.0
, the library includes a new algorithm, named XXH3
,
able to generate 64 and 128-bits hashes.
The new algorithm is much faster than its predecessors, for both long and small inputs, as can be observed in following graphs :
The algorithm is currently labeled experimental, its return values can still change in future versions. It can already be used for ephemeral data, and for tests, but avoid storing long-term hash values yet.
To access experimental prototypes, one need to unlock their declaration using macro XXH_STATIC_LINKING_ONLY
.
XXH3
will be stabilized in a future version.
This period is used to collect users' feedback.
Beyond the C reference version, xxHash is also available on many programming languages, thanks to great contributors. They are listed here.
- 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.