各种Hash函数

各种Hash函数

C语言源程序：

// RS Hash Function
unsigned int RSHash(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(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(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(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(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);
}

// SDBM Hash Function
unsigned int SDBMHash(char *str)
{
unsigned int hash = 0;

while (*str)
{
   hash = (*str++) + (hash << 6) + (hash << 16) - hash;
}

return (hash & 0x7FFFFFFF);
}

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

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

return (hash & 0x7FFFFFFF);
}

// AP Hash Function
unsigned int APHash(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);
}

 

note：
1、PJWHash采用了sizeof()运算符
2、RSHash、JSHash、BKDRHash、SDBMHash、DJBHash均使用了C语言滴一个特殊特性——溢出部分自动舍去，即对溢出滴变量采取and $FFFFFFFF(& 0xFFFFFFFF)处理

 

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