Port of the xxHash library to C++17.
Compiler Min. Version MSVC (Visual Studio) 19.1 (VS 2017.3 P2) clang 3.9 gcc 7// standalone hash
std::array<int, 4> input {322, 2137, 42069, 65536};
xxh::hash_t<32> hash = xxh::xxhash<32>(input);
// hash streaming
std::array<unsigned char, 512> buffer;
xxh::hash_state_t<64> hash_stream;
while (fill_buffer(buffer))
{
hash_stream.update(buffer);
}
xxh::hash_t<64> final_hash = hash_stream.digest();
The template argument specifies whether the algorithm will use the 32 or 64 bit version. Other values are not allowed. Typedefs hash32_t, hash64_t, hash_state32_t and hash_state64_t are provided.
xxh::xxhash and xxh::hash_state_t::update provide several convenient overloads, all accepting optional seed and endianness arguments:
const void* + size_t pairconst std::vector<T>&const std::basic_string<T>&const std::array<T, N>&const std::initializer_list<T>&The library is provided as a single standalone header, for static linking only. No build instructions are nessessary.
xxHash - Extremely fast hash algorithmxxHash 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).
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 10Q.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-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/sThe library file xxhash.hpp is BSD licensed.
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_CPU_LITTLE_ENDIAN : if defined to 0, sets the native endianness to big endian, if defined to 1, sets the native endianness to little endian, if left undefined, the endianness is resolved at runtime, before main is called, at the cost of endianness not being constexpr.
XXH_FORCE_MEMORY_ACCESS : if defined to 2, enables unaligned reads as an optimization, this is not standard compliant, if defined to 1, enables the use of packed attribute for optimization, only defined for gcc and icc otherwise, uses the default fallback method (memcpy)
Beyond the C reference version, xxHash is also available on many programming languages, thanks to great contributors. They are listed here.
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