常见HASH算法

/*
**************************************************************************
*                                                                        *
*          General Purpose Hash Function Algorithms Library              *
*                                                                        *
* Author: Arash Partow - 2002                                            *
* URL: http://www.partow.net                                             *
* URL: http://www.partow.net/programming/hashfunctions/index.html        *
*                                                                        *
* Copyright notice:                                                      *
* Free use of the General Purpose Hash Function Algorithms Library is    *
* permitted under the guidelines and in accordance with the most current *
* version of the Common Public License.                                  *
* http://www.opensource.org/licenses/cpl1.0.php                          *
*                                                                        *
**************************************************************************
*/

class GeneralHashFunctionLibrary
{

public long RSHash(String str)
{
int b     = 378551;
int a     = 63689;
long hash = 0;

for(int i = 0; i < str.length(); i++)
{
hash = hash * a + str.charAt(i);
a    = a * b;
}

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

public long JSHash(String str)
{
long hash = 1315423911;

for(int i = 0; i < str.length(); i++)
{
hash ^= ((hash << 5) + str.charAt(i) + (hash >> 2));
}

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

public long PJWHash(String str)
{
long BitsInUnsignedInt = (long)(4 * 8);
long ThreeQuarters     = (long)((BitsInUnsignedInt  * 3) / 4);
long OneEighth         = (long)(BitsInUnsignedInt / 8);
long HighBits          = (long)(0xFFFFFFFF) << (BitsInUnsignedInt - OneEighth);
long hash              = 0;
long test              = 0;

for(int i = 0; i < str.length(); i++)
{
hash = (hash << OneEighth) + str.charAt(i);

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

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

public long ELFHash(String str)
{
long hash = 0;
long x    = 0;

for(int i = 0; i < str.length(); i++)
{
hash = (hash << 4) + str.charAt(i);

if((x = hash & 0xF0000000L) != 0)
{
hash ^= (x >> 24);
}
hash &= ~x;
}

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

public long BKDRHash(String str)
{
long seed = 131; // 31 131 1313 13131 131313 etc..
long hash = 0;

for(int i = 0; i < str.length(); i++)
{
hash = (hash * seed) + str.charAt(i);
}

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

public long SDBMHash(String str)
{
long hash = 0;

for(int i = 0; i < str.length(); i++)
{
hash = str.charAt(i) + (hash << 6) + (hash << 16) - hash;
}

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

public long DJBHash(String str)
{
long hash = 5381;

for(int i = 0; i < str.length(); i++)
{
hash = ((hash << 5) + hash) + str.charAt(i);
}

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

public long DEKHash(String str)
{
long hash = str.length();

for(int i = 0; i < str.length(); i++)
{
hash = ((hash << 5) ^ (hash >> 27)) ^ str.charAt(i);
}

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

public long BPHash(String str)
{
long hash = 0;

for(int i = 0; i < str.length(); i++)
{
hash = hash << 7 ^ str.charAt(i);
}

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

public long FNVHash(String str)
{
long fnv_prime = 0x811C9DC5;
long hash = 0;

for(int i = 0; i < str.length(); i++)
{
hash *= fnv_prime;
hash ^= str.charAt(i);
}

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

public long APHash(String str)
{
long hash = 0xAAAAAAAA;

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

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

}