1 2 // Copyright 2008-2009 Daniel James. 3 // Distributed under the Boost Software License, Version 1.0. (See accompanying 4 // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) 5 6 // This code is also released into the public domain. 7 8 // Algorithm from: http://www.isthe.com/chongo/tech/comp/fnv/ 9 10 #include <string> 11 12 namespace hash 13 { 14 template <std::size_t FnvPrime, std::size_t OffsetBasis> 15 struct basic_fnv_1 16 { operator ()hash::basic_fnv_117 std::size_t operator()(std::string const& text) const 18 { 19 std::size_t hash = OffsetBasis; 20 for(std::string::const_iterator it = text.begin(), end = text.end(); 21 it != end; ++it) 22 { 23 hash *= FnvPrime; 24 hash ^= *it; 25 } 26 27 return hash; 28 } 29 }; 30 31 template <std::size_t FnvPrime, std::size_t OffsetBasis> 32 struct basic_fnv_1a 33 { operator ()hash::basic_fnv_1a34 std::size_t operator()(std::string const& text) const 35 { 36 std::size_t hash = OffsetBasis; 37 for(std::string::const_iterator it = text.begin(), end = text.end(); 38 it != end; ++it) 39 { 40 hash ^= *it; 41 hash *= FnvPrime; 42 } 43 44 return hash; 45 } 46 }; 47 48 // For 32 bit machines: 49 const std::size_t fnv_prime = 16777619u; 50 const std::size_t fnv_offset_basis = 2166136261u; 51 52 // For 64 bit machines: 53 // const std::size_t fnv_prime = 1099511628211u; 54 // const std::size_t fnv_offset_basis = 14695981039346656037u; 55 56 // For 128 bit machines: 57 // const std::size_t fnv_prime = 309485009821345068724781401u; 58 // const std::size_t fnv_offset_basis = 59 // 275519064689413815358837431229664493455u; 60 61 // For 256 bit machines: 62 // const std::size_t fnv_prime = 63 // 374144419156711147060143317175368453031918731002211u; 64 // const std::size_t fnv_offset_basis = 65 // 100029257958052580907070968620625704837092796014241193945225284501741471925557u; 66 67 typedef basic_fnv_1<fnv_prime, fnv_offset_basis> fnv_1; 68 typedef basic_fnv_1a<fnv_prime, fnv_offset_basis> fnv_1a; 69 } 70