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  • 一些常用的字符串hash函数

     General Hash Function Source Code:

    unsigned int RSHash(const std::string& str)
    {
        unsigned int b    = 378551;
        unsigned int a    = 63689;
        unsigned int hash = 0;
    
        for(std::size_t i = 0; i < str.length(); i++)
        {
            hash = hash * a + str[i];
            a    = a * b;
        }
    
        return hash;
    }
    /* End Of RS Hash Function */
    
    
    unsigned int JSHash(const std::string& str)
    {
        unsigned int hash = 1315423911;
    
        for(std::size_t i = 0; i < str.length(); i++)
        {
            hash ^= ((hash << 5) + str[i] + (hash >> 2));
        }
    
        return hash;
    }
    /* End Of JS Hash Function */
    
    
    unsigned int PJWHash(const std::string& str)
    {
        unsigned int BitsInUnsignedInt = (unsigned int)(sizeof(unsigned int) * 8);
        unsigned int ThreeQuarters     = (unsigned int)((BitsInUnsignedInt  * 3) / 4);
        unsigned int OneEighth         = (unsigned int)(BitsInUnsignedInt / 8);
        unsigned int HighBits          = (unsigned int)(0xFFFFFFFF) << (BitsInUnsignedInt - OneEighth);
        unsigned int hash              = 0;
        unsigned int test              = 0;
    
        for(std::size_t i = 0; i < str.length(); i++)
        {
            hash = (hash << OneEighth) + str[i];
    
            if((test = hash & HighBits)  != 0)
            {
                hash = (( hash ^ (test >> ThreeQuarters)) & (~HighBits));
            }
        }
    
        return hash;
    }
    /* End Of  P. J. Weinberger Hash Function */
    
    
    unsigned int ELFHash(const std::string& str)
    {
        unsigned int hash = 0;
        unsigned int x    = 0;
    
        for(std::size_t i = 0; i < str.length(); i++)
        {
            hash = (hash << 4) + str[i];
            if((x = hash & 0xF0000000L) != 0)
            {
                hash ^= (x >> 24);
            }
            hash &= ~x;
        }
    
        return hash;
    }
    /* End Of ELF Hash Function */
    
    
    unsigned int BKDRHash(const std::string& str)
    {
        unsigned int seed = 131; // 31 131 1313 13131 131313 etc..
        unsigned int hash = 0;
    
        for(std::size_t i = 0; i < str.length(); i++)
        {
            hash = (hash * seed) + str[i];
        }
    
        return hash;
    }
    /* End Of BKDR Hash Function */
    
    
    unsigned int SDBMHash(const std::string& str)
    {
        unsigned int hash = 0;
    
        for(std::size_t i = 0; i < str.length(); i++)
        {
            hash = str[i] + (hash << 6) + (hash << 16) - hash;
        }
    
        return hash;
    }
    /* End Of SDBM Hash Function */
    
    
    unsigned int DJBHash(const std::string& str)
    {
        unsigned int hash = 5381;
    
        for(std::size_t i = 0; i < str.length(); i++)
        {
            hash = ((hash << 5) + hash) + str[i];
        }
    
        return hash;
    }
    /* End Of DJB Hash Function */
    
    
    unsigned int DEKHash(const std::string& str)
    {
        unsigned int hash = static_cast<unsigned int>(str.length());
    
        for(std::size_t i = 0; i < str.length(); i++)
        {
            hash = ((hash << 5) ^ (hash >> 27)) ^ str[i];
        }
    
        return hash;
    }
    /* End Of DEK Hash Function */
    
    
    unsigned int BPHash(const std::string& str)
    {
        unsigned int hash = 0;
        for(std::size_t i = 0; i < str.length(); i++)
        {
            hash = hash << 7 ^ str[i];
        }
    
        return hash;
    }
    /* End Of BP Hash Function */
    
    
    unsigned int FNVHash(const std::string& str)
    {
        const unsigned int fnv_prime = 0x811C9DC5;
        unsigned int hash = 0;
        for(std::size_t i = 0; i < str.length(); i++)
        {
            hash *= fnv_prime;
            hash ^= str[i];
        }
    
        return hash;
    }
    /* End Of FNV Hash Function */
    
    
    unsigned int APHash(const std::string& str)
    {
        unsigned int hash = 0xAAAAAAAA;
    
        for(std::size_t i = 0; i < str.length(); i++)
        {
            hash ^= ((i & 1) == 0) ? (  (hash <<  7) ^ str[i] * (hash >> 3)) :
                (~((hash << 11) + (str[i] ^ (hash >> 5))));
        }
    
        return hash;
    }
    /* End Of AP Hash Function */
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  • 原文地址:https://www.cnblogs.com/luxiaoxun/p/2625659.html
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