hashfuncs.c


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/* hashfuncs.c
 *
 * Hash Functions
 *
 * notes: aphash may not be correct 
 *
 */

#include "hashfuncs.h"

/* does not mod by the size of the hash table, simple and clever,
 * this allows seamless retrieval of collided elements */
unsigned int defaulthash(const char *key)
{
    unsigned int hash = 0;
    
    for ( ; *key; key++)
        hash += (unsigned char) *key;

    return hash;
}

unsigned int rshash(const char *key)
{
    unsigned int b = 378551;
    unsigned int a = 63689;
    unsigned int hash = 0;

    for ( ; *key; key++)
    {
        hash = hash * a + (*key);
        a = a * b;
    }

    return hash;
}

unsigned int jshash(const char *key)
{
    unsigned int hash = 1315423911;

    for ( ; *key; key++)
        hash ^= ((hash << 5) + ((unsigned char) (*key)) + (hash >> 2));

    return hash;
}

unsigned int pjwhash(const char *key)
{
    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;

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

    return hash;
}

unsigned int elfhash(const char *key)
{
    unsigned int hash = 0;
    unsigned int x = 0;

    for ( ; *key; key++)
    {
        hash = (hash << 4) + (*key);

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

      hash &= ~x;
    }

    return hash;
}

unsigned int bkdrhash(const char *key)
{
    unsigned int seed = 131; /* 31 131 1313 13131 131313 etc.. */
    unsigned int hash = 0;

    for ( ; *key; key++)
        hash = (hash * seed) + (*key);
 
    return hash;
}

unsigned int sdbmhash(const char *key)
{
    unsigned int hash = 0;

    for ( ; *key; key++)
        hash = (*key) + (hash << 6) + (hash << 16) - hash;

    return hash;
}

unsigned int djbhash(const char *key)
{
    unsigned int hash = 5381;

    for ( ; *key; key++)
        hash = ((hash << 5) + hash) + (*key);

    return hash;
}

unsigned int dekhash(const char *key)
{
    unsigned int hash = strlen(key);

    for ( ; *key; key++)
        hash = ((hash << 5) ^ (hash >> 27)) ^ (*key);

    return hash;
}

unsigned int bphash(const char *key)
{
    unsigned int hash = 0;

    for ( ; *key; key++)
        hash = hash << 7 ^ (*key);

    return hash;
}

unsigned int fnvhash(const char *key)
{
    const unsigned int fnv_prime = 0x811C9DC5;
    unsigned int hash = 0;

    for ( ; *key; key++)
    {
        hash *= fnv_prime;
        hash ^= (*key);
    }

    return hash;
}

unsigned int aphash(const char *key)
{
    unsigned int hash = 0xAAAAAAAA;
    unsigned int i = strlen(key);

    for ( ; *key; key++)
    {
        hash ^= ((i & 1) == 0) ? (  (hash <<  7) ^ (const unsigned int) (*key) * (hash >> 3)) :
                               (~((hash << 11) + ((const unsigned int) (*key) ^ (hash >> 5) )));
    }

    return hash;
}