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标题: 各种hash函数 [打印本页]

作者: lenky0401 时间: 2013-10-8 20:23
标题: 各种hash函数
unsigned int SDBMHash(const char *str)
{
unsigned int hash = 0;

while (*str)
{
      // equivalent to: hash = 65599*hash + (*str++);
      hash = (*str++) + (hash << 6) + (hash << 16) - hash;
}

return (hash & 0x7FFFFFFF);
}

// RS Hash Function
unsigned int RSHash(const char *str)
{
unsigned int b = 378551;
unsigned int a = 63689;
unsigned int hash = 0;

while (*str)
{
      hash = hash * a + (*str++);
      a *= b;
}

return (hash & 0x7FFFFFFF);
}

// JS Hash Function
unsigned int JSHash(const char *str)
{
unsigned int hash = 1315423911;

while (*str)
{
      hash ^= ((hash << 5) + (*str++) + (hash >> 2));
}

return (hash & 0x7FFFFFFF);
}

// P. J. Weinberger Hash Function
unsigned int PJWHash(const char *str)
{
unsigned int BitsInUnignedInt = (unsigned int)(sizeof(unsigned int) * 8);
unsigned int ThreeQuarters = (unsigned int)((BitsInUnignedInt * 3) / 4);
unsigned int OneEighth = (unsigned int)(BitsInUnignedInt / 8);
unsigned int HighBits = (unsigned int)(0xFFFFFFFF) << (BitsInUnignedInt - OneEighth);
unsigned int hash = 0;
unsigned int test = 0;

while (*str)
{
hash = (hash << OneEighth) + (*str++);
if ((test = hash & HighBits) != 0)
{
hash = ((hash ^ (test >> ThreeQuarters)) & (~HighBits));
}
}

return (hash & 0x7FFFFFFF);
}

// ELF Hash Function
unsigned int ELFHash(const char *str)
{
unsigned int hash = 0;
unsigned int x  = 0;

while (*str)
{
      hash = (hash << 4) + (*str++);
            if ((x = hash & 0xF0000000L) != 0)
            {
                     hash ^= (x >> 24);
         hash &= ~x;
      }
}

return (hash & 0x7FFFFFFF);
}

// BKDR Hash Function
unsigned int BKDRHash(const char *str)
{
unsigned int seed = 131; // 31 131 1313 13131 131313 etc..
unsigned int hash = 0;

while (*str)
{
      hash = hash * seed + (*str++);
}

return (hash & 0x7FFFFFFF);
}

// DJB Hash Function
unsigned int DJBHash(const char *str)
{
unsigned int hash = 5381;

while (*str)
{
      hash += (hash << 5) + (*str++);
}

return (hash & 0x7FFFFFFF);
}

// AP Hash Function
unsigned int APHash(const char *str)
{
unsigned int hash = 0;
int i;

for (i=0; *str; i++)
{
      if ((i & 1) == 0)
      {
         hash ^= ((hash << 7) ^ (*str++) ^ (hash >> 3));
      }
      else
      {
         hash ^= (~((hash << 11) ^ (*str++) ^ (hash >> 5)));
      }
}

return (hash & 0x7FFFFFFF);
}

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