diff --git a/hash.cpp b/hash.cpp index 2a7cada1..b85178a7 100644 --- a/hash.cpp +++ b/hash.cpp @@ -46,3 +46,44 @@ util::wang64 (uint64_t key) { } + +// 32: 2^ 24 + 2^8 + 0x93 +// 64: 2^ 40 + 2^8 + 0xb3 +// 128: 2^ 88 + 2^8 + 0x3B +// 256: 2^168 + 2^8 + 0x63 +// 512: 2^344 + 2^8 + 0x57 +// 1024: 2^680 + 2^8 + 0x8D +static const uint32_t FNV_1a_32_PRIME = 16777619U; +static const uint64_t FNV_1a_64_PRIME = 1099511628211U; + +// Bias is the FNV-0 hash of "chongo /\\../\\" +static const uint32_t FNV_1a_32_BIAS = 2166136261U; +static const uint64_t FNV_1a_64_BIAS = 14695981039346656037U; + + +uint32_t +util::fnv1a32 (const void *_data, size_t size) { + const uint8_t *data = static_cast (_data); + uint32_t result = FNV_1a_32_BIAS; + + for (size_t i = 0; i < size; ++i) { + result ^= data[i]; + result *= FNV_1a_32_PRIME; + } + + return result; +} + + +uint64_t +util::fnv1a64 (const void *_data, size_t size) { + const uint8_t *data = static_cast (_data); + uint64_t result = FNV_1a_64_BIAS; + + for (size_t i = 0; i < size; ++i) { + result ^= data[i]; + result *= FNV_1a_64_PRIME; + } + + return result; +} diff --git a/hash.hpp b/hash.hpp index 25c1cc61..d207e2a9 100644 --- a/hash.hpp +++ b/hash.hpp @@ -29,6 +29,10 @@ namespace util { uint32_t wang32 (uint32_t key); uint64_t wang64 (uint64_t key); + // Fast and general hashing using FNV-1a + uint32_t fnv1a32 (const void *, size_t); + uint64_t fnv1a64 (const void *, size_t); + // General hashes for when you really just don't care about implementation inline uint32_t hash (uint32_t key) { return wang32 (key); } inline uint64_t hash (uint64_t key) { return wang64 (key); }