github.com/moontrade/nogc@v0.1.7/collections/tree/hash.h (about)

     1  #ifndef HASH_H
     2  #define HASH_H
     3  
     4  #pragma once
     5  
     6  #include <cstddef>
     7  #include <cstdint>
     8  #include <string>
     9  #include <type_traits>
    10  
    11  static const char* HashName = "FNV1a";
    12  
    13  static size_t fnv1a(uint8_t const* data, size_t size) {
    14  #if SIZE_MAX == UINT32_MAX
    15      static constexpr size_t FNV_offset_basis = UINT64_C(14695981039346656037);
    16      static constexpr size_t FNV_prime = UINT64_C(1099511628211);
    17  #else
    18      static constexpr size_t FNV_offset_basis = UINT32_C(2166136261);
    19      static constexpr size_t FNV_prime = UINT32_C(16777619);
    20  #endif
    21      size_t val = FNV_offset_basis;
    22      for (size_t i = 0; i < size; ++i) {
    23          val ^= static_cast<size_t>(data[i]);
    24          val *= FNV_prime;
    25      }
    26      return val;
    27  }
    28  
    29  // Visual Studio uses a FNV1a implementation.
    30  template <typename T>
    31  struct Hash {
    32      size_t operator()(T const& key) const {
    33          return fnv1a(reinterpret_cast<uint8_t const*>(&key), sizeof(T));
    34      }
    35  };
    36  
    37  // Visual Studio uses a FNV1a implementation.
    38  template <>
    39  struct Hash<std::string> {
    40      size_t operator()(std::string const& key) const {
    41          return fnv1a(reinterpret_cast<uint8_t const*>(key.data()), key.size());
    42      }
    43  };
    44  
    45  #endif //HASH_H