fast_hash.hpp

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// fast_hash.hpp
/*
 *  Copyright (c) 2018, 2020 Leigh Johnston.
 *
 *  All rights reserved.
 *
 *  Redistribution and use in source and binary forms, with or without
 *  modification, are permitted provided that the following conditions are
 *  met:
 *
 *     * Redistributions of source code must retain the above copyright
 *       notice, this list of conditions and the following disclaimer.
 *
 *     * Redistributions in binary form must reproduce the above copyright
 *       notice, this list of conditions and the following disclaimer in the
 *       documentation and/or other materials provided with the distribution.
 *
 *     * Neither the name of Leigh Johnston nor the names of any
 *       other contributors to this software may be used to endorse or
 *       promote products derived from this software without specific prior
 *       written permission.
 *
 *  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
 *  IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
 *  THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 *  PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
 *  CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 *  EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 *  PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
 *  PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
 *  LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
 *  NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 *  SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
 
#pragma once
 
#include <neolib/neolib.hpp>
 
namespace neolib
{
    namespace detail
    {
        template <typename T>
        inline T fast_hash(const void* aInput, std::size_t aLength);
 
        // https://en.wikipedia.org/wiki/Fowler%E2%80%93Noll%E2%80%93Vo_hash_function
 
        template <>
        inline uint32_t fast_hash<uint32_t>(const void* aInput, std::size_t aLength)
        {
            uint32_t hash = 2166136261u;
            const uint8_t* octet = static_cast<const uint8_t*>(aInput);
            auto endOctet = octet + aLength;
            while (octet != endOctet)
            {
                hash = hash ^ *octet++;
                hash = hash * 16777619u;
            }
            return hash;
        }
 
        template <>
        inline uint64_t fast_hash<uint64_t>(const void* aInput, std::size_t aLength)
        {
            uint64_t hash = 14695981039346656037ull;
            const uint8_t* octet = static_cast<const uint8_t*>(aInput);
            auto endOctet = octet + aLength;
            while (octet != endOctet)
            {
                hash = hash ^ *octet++;
                hash = hash * 1099511628211ull;
            }
            return hash;
        }
    }
 
    template <typename T>
    inline T fast_hash(const void* aInput, std::size_t aLength)
    {
        return detail::fast_hash<T>(aInput, aLength);
    }
 
    inline uint32_t fast_hash(const void* aInput, std::size_t aLength)
    {
        return fast_hash<uint32_t>(aInput, aLength);
    }
}