include/o3tl/hash_combine.hxx

   1 /* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
   2 /*
   3  * This file is part of the LibreOffice project.
   4  *
   5  * This Source Code Form is subject to the terms of the Mozilla Public
   6  * License, v. 2.0. If a copy of the MPL was not distributed with this
   7  * file, You can obtain one at http://mozilla.org/MPL/2.0/.
   8  */
   9
  10 #pragma once
  11
  12 #include <cstddef>
  13 #include <functional>
  14 #include <type_traits>
  15
  16 namespace o3tl
  17 {
  18 template <typename T, typename N>
  19 inline std::enable_if_t<(sizeof(N) == 4)> hash_combine(N& nSeed, T const* pValue, size_t nCount)
  20 {
  21     static_assert(sizeof(nSeed) == 4);
  22     for (size_t i = 0; i < nCount; ++i)
  23     {
  24         nSeed ^= std::hash<T>{}(*pValue) + 0x9E3779B9u + (nSeed << 6) + (nSeed >> 2);
  25         ++pValue;
  26     }
  27 }
  28
  29 template <typename T, typename N>
  30 inline std::enable_if_t<(sizeof(N) == 4)> hash_combine(N& nSeed, T const& nValue)
  31 {
  32     static_assert(sizeof(nSeed) == 4);
  33     nSeed ^= std::hash<T>{}(nValue) + 0x9E3779B9u + (nSeed << 6) + (nSeed >> 2);
  34 }
  35
  36 template <typename T, typename N>
  37 inline std::enable_if_t<(sizeof(N) == 8)> hash_combine(N& nSeed, T const* pValue, size_t nCount)
  38 {
  39     static_assert(sizeof(nSeed) == 8);
  40     for (size_t i = 0; i < nCount; ++i)
  41     {
  42         nSeed ^= std::hash<T>{}(*pValue) + 0x9E3779B97F4A7C15llu + (nSeed << 12) + (nSeed >> 4);
  43         ++pValue;
  44     }
  45 }
  46
  47 template <typename T, typename N>
  48 inline std::enable_if_t<(sizeof(N) == 8)> hash_combine(N& nSeed, T const& nValue)
  49 {
  50     static_assert(sizeof(nSeed) == 8);
  51     nSeed ^= std::hash<T>{}(nValue) + 0x9E3779B97F4A7C15llu + (nSeed << 12) + (nSeed >> 4);
  52 }
  53 }
  54
  55 /* vim:set shiftwidth=4 softtabstop=4 expandtab cinoptions=b1,g0,N-s cinkeys+=0=break: */