常用Hash算法(C语言的简单实现)

如下所示：

#include "GeneralHashFunctions.h"

unsigned int RSHash(char* str, unsigned int len)
{
 unsigned int b  = 378551;
 unsigned int a  = 63689;
 unsigned int hash = 0;
 unsigned int i  = 0;

for(i = 0; i < len; str++, i++)
 {
  hash = hash * a + (*str);
  a  = a * b;
 }

return hash;
}
/* End Of RS Hash Function */

unsigned int JSHash(char* str, unsigned int len)
{
 unsigned int hash = 1315423911;
 unsigned int i  = 0;

for(i = 0; i < len; str++, i++)
 {
  hash ^= ((hash << 5) + (*str) + (hash >> 2));
 }

return hash;
}
/* End Of JS Hash Function */

unsigned int PJWHash(char* str, unsigned int len)
{
 const unsigned int BitsInUnsignedInt = (unsigned int)(sizeof(unsigned int) * 8);
 const unsigned int ThreeQuarters   = (unsigned int)((BitsInUnsignedInt * 3) / 4);
 const unsigned int OneEighth     = (unsigned int)(BitsInUnsignedInt / 8);
 const unsigned int HighBits     = (unsigned int)(0xFFFFFFFF) << (BitsInUnsignedInt - OneEighth);
 unsigned int hash       = 0;
 unsigned int test       = 0;
 unsigned int i         = 0;

for(i = 0; i < len; str++, i++)
 {
  hash = (hash << OneEighth) + (*str);

if((test = hash & HighBits) != 0)
  {
    hash = (( hash ^ (test >> ThreeQuarters)) & (~HighBits));
  }
 }

return hash;
}
/* End Of P. J. Weinberger Hash Function */

unsigned int ELFHash(char* str, unsigned int len)
{
 unsigned int hash = 0;
 unsigned int x  = 0;
 unsigned int i  = 0;

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

return hash;
}
/* End Of ELF Hash Function */

unsigned int BKDRHash(char* str, unsigned int len)
{
 unsigned int seed = 131; /* 31 131 1313 13131 131313 etc.. */
 unsigned int hash = 0;
 unsigned int i  = 0;

for(i = 0; i < len; str++, i++)
 {
  hash = (hash * seed) + (*str);
 }

return hash;
}
/* End Of BKDR Hash Function */

unsigned int SDBMHash(char* str, unsigned int len)
{
 unsigned int hash = 0;
 unsigned int i  = 0;

for(i = 0; i < len; str++, i++)
 {
  hash = (*str) + (hash << 6) + (hash << 16) - hash;
 }

return hash;
}
/* End Of SDBM Hash Function */

unsigned int DJBHash(char* str, unsigned int len)
{
 unsigned int hash = 5381;
 unsigned int i  = 0;

for(i = 0; i < len; str++, i++)
 {
  hash = ((hash << 5) + hash) + (*str);
 }

return hash;
}
/* End Of DJB Hash Function */

unsigned int DEKHash(char* str, unsigned int len)
{
 unsigned int hash = len;
 unsigned int i  = 0;

for(i = 0; i < len; str++, i++)
 {
  hash = ((hash << 5) ^ (hash >> 27)) ^ (*str);
 }
 return hash;
}
/* End Of DEK Hash Function */

unsigned int BPHash(char* str, unsigned int len)
{
 unsigned int hash = 0;
 unsigned int i  = 0;
 for(i = 0; i < len; str++, i++)
 {
  hash = hash << 7 ^ (*str);
 }

return hash;
}
/* End Of BP Hash Function */

unsigned int FNVHash(char* str, unsigned int len)
{
 const unsigned int fnv_prime = 0x811C9DC5;
 unsigned int hash   = 0;
 unsigned int i     = 0;

for(i = 0; i < len; str++, i++)
 {
  hash *= fnv_prime;
  hash ^= (*str);
 }

return hash;
}
/* End Of FNV Hash Function */

unsigned int APHash(char* str, unsigned int len)
{
 unsigned int hash = 0xAAAAAAAA;
 unsigned int i  = 0;

for(i = 0; i < len; str++, i++)
 {
  hash ^= ((i & 1) == 0) ? ( (hash << 7) ^ (*str) * (hash >> 3)) :
               (~((hash << 11) + ((*str) ^ (hash >> 5))));
 }

return hash;
}
/* End Of AP Hash Function */