CMUtil/src/hash/MurmurHash3.cpp

#include<hgl/util/hash/Hash.h>

namespace hgl
{
    namespace util
    {
        namespace
        {
            //本代码来自Github Copilot
            //MurmurHash 是一种高性能的哈希算法，特别适用于哈希表。它具有良好的分布性和较低的碰撞率。

            uint32_t CountMurmurHash3(const void *key, int len, uint32_t seed)
            {
                const uint8_t *data = (const uint8_t *)key;
                const int nblocks = len / 4;
                uint32_t h1 = seed;

                const uint32_t c1 = 0xcc9e2d51;
                const uint32_t c2 = 0x1b873593;

                // Body
                const uint32_t *blocks = (const uint32_t *)(data + nblocks * 4);
                for (int i = -nblocks; i; i++) {
                    uint32_t k1 = blocks[i];

                    k1 *= c1;
                    k1 = (k1 << 15) | (k1 >> (32 - 15));
                    k1 *= c2;

                    h1 ^= k1;
                    h1 = (h1 << 13) | (h1 >> (32 - 13));
                    h1 = h1 * 5 + 0xe6546b64;
                }

                // Tail
                const uint8_t *tail = (const uint8_t *)(data + nblocks * 4);
                uint32_t k1 = 0;

                switch (len & 3)
                {
                    case 3:
                        k1 ^= tail[2] << 16;
                    case 2:
                        k1 ^= tail[1] << 8;
                    case 1:
                        k1 ^= tail[0];
                        k1 *= c1;
                        k1 = (k1 << 15) | (k1 >> (32 - 15));
                        k1 *= c2;
                        h1 ^= k1;
                }

                // Finalization
                h1 ^= len;
                h1 ^= h1 >> 16;
                h1 *= 0x85ebca6b;
                h1 ^= h1 >> 13;
                h1 *= 0xc2b2ae35;
                h1 ^= h1 >> 16;

                return h1;
            }
        }//namespace

        class MurmurHash3:public Hash
        {
            uint32_t result;

        public:

            MurmurHash3():Hash(4,"MurmurHash3")
            {}
            void Init()override
            {
                result=0;
            }
            void Update(const void *input,uint inputLen)override
            {
                result=CountMurmurHash3(input,inputLen,result);
            }
            void Final(void *digest)override
            {
                *(uint32_t *)digest=result;
            }
        };//class MurmurHash3

        template<> Hash *CreateHash<HASH::Murmur3>()
        {
            return(new MurmurHash3);
        }
    }//namespace util
}//namespace hgl