diff --git a/examples/hash_functions/fnv-1.hpp b/examples/hash_functions/fnv-1.hpp new file mode 100644 index 00000000..fcfd8cdf --- /dev/null +++ b/examples/hash_functions/fnv-1.hpp @@ -0,0 +1,66 @@ +// See: http://www.isthe.com/chongo/tech/comp/fnv/ + +#include + +namespace hash +{ + template + struct basic_fnv_1 + { + std::size_t operator()(std::string const& text) + { + std::size_t hash = OffsetBias; + for(std::string::const_iterator it = text.begin(), end = text.end(); + it != end; ++it) + { + hash *= FnvPrime; + hash ^= *it; + } + + return hash; + } + }; + + template + struct basic_fnv_1a + { + std::size_t operator()(std::string const& text) + { + std::size_t hash = OffsetBias; + for(std::string::const_iterator it = text.begin(), end = text.end(); + it != end; ++it) + { + hash ^= *it; + hash *= FnvPrime; + } + + return hash; + } + }; + + // TODO: Select Bias & Prime base on the size of std::size_t. + // + // 32 bit FNV_prime = 16777619 + // 64 bit FNV_prime = 1099511628211 + // 128 bit FNV_prime = 309485009821345068724781401 + // 256 bit FNV_prime = 374144419156711147060143317175368453031918731002211 + // + // 32 bit offset_basis = 2166136261 + // 64 bit offset_basis = 14695981039346656037 + // 128 bit offset_basis = 275519064689413815358837431229664493455 + // 256 bit offset_basis = 100029257958052580907070968620625704837092796014241193945225284501741471925557 + + const std::size_t fnv_prime = 16777619; + // 64 bit FNV_prime = 1099511628211 + // 128 bit FNV_prime = 309485009821345068724781401 + // 256 bit FNV_prime = 374144419156711147060143317175368453031918731002211 + + const std::size_t fnv_offset_bias = 2166136261; + // 64 bit offset_basis = 14695981039346656037 + // 128 bit offset_basis = 275519064689413815358837431229664493455 + // 256 bit offset_basis = 100029257958052580907070968620625704837092796014241193945225284501741471925557 + + typedef basic_fnv_1 fnv_1; + typedef basic_fnv_1a fnv_1a; + +}