hash_combine.hxx

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/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
/*
 * This file is part of the LibreOffice project.
 *
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/.
 */
 
#pragma once
 
#include <cstddef>
#include <functional>
#include <type_traits>
 
namespace o3tl
{
template <typename T, typename N>
inline std::enable_if_t<(sizeof(N) == 4)> hash_combine(N& nSeed, T const* pValue, size_t nCount)
{
    static_assert(sizeof(nSeed) == 4);
    for (size_t i = 0; i < nCount; ++i)
    {
        nSeed ^= std::hash<T>{}(*pValue) + 0x9E3779B9u + (nSeed << 6) + (nSeed >> 2);
        ++pValue;
    }
}
 
template <typename T, typename N>
inline std::enable_if_t<(sizeof(N) == 4)> hash_combine(N& nSeed, T const& nValue)
{
    static_assert(sizeof(nSeed) == 4);
    nSeed ^= std::hash<T>{}(nValue) + 0x9E3779B9u + (nSeed << 6) + (nSeed >> 2);
}
 
template <typename T, typename N>
inline std::enable_if_t<(sizeof(N) == 8)> hash_combine(N& nSeed, T const* pValue, size_t nCount)
{
    static_assert(sizeof(nSeed) == 8);
    for (size_t i = 0; i < nCount; ++i)
    {
        nSeed ^= std::hash<T>{}(*pValue) + 0x9E3779B97F4A7C15llu + (nSeed << 12) + (nSeed >> 4);
        ++pValue;
    }
}
 
template <typename T, typename N>
inline std::enable_if_t<(sizeof(N) == 8)> hash_combine(N& nSeed, T const& nValue)
{
    static_assert(sizeof(nSeed) == 8);
    nSeed ^= std::hash<T>{}(nValue) + 0x9E3779B97F4A7C15llu + (nSeed << 12) + (nSeed >> 4);
}
}
 
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