hash_32.c

/*
 * hash_32 - 32 bit Fowler/Noll/Vo hash code
 *
 *
 ***
 *
 * Fowler/Noll/Vo hash
 *
 * The basis of this hash algorithm was taken from an idea sent
 * as reviewer comments to the IEEE POSIX P1003.2 committee by:
 *
 *      Phong Vo (http://www.research.att.com/info/kpv/)
 *      Glenn Fowler (http://www.research.att.com/~gsf/)
 *
 * In a subsequent ballot round:
 *
 *      Landon Curt Noll (http://reality.sgi.com/chongo/)
 *
 * improved on their algorithm.  Some people tried this hash
 * and found that it worked rather well.  In an EMail message
 * to Landon, they named it the ``Fowler/Noll/Vo'' or FNV hash.
 *
 * FNV hashes are architected to be fast while maintaining a low
 * collision rate. The FNV speed allows one to quickly hash lots
 * of data while maintaining a reasonable collision rate.  See:
 *
 *      http://reality.sgi.com/chongo/tech/comp/fnv/
 *
 * for more details as well as other forms of the FNV hash.
 ***
 *
 * NOTE: The FNV-0 historic hash is not recommended.  One should use
 *	 the FNV-1 hash instead.
 *
 * To use the 32 bit FNV-0 historic hash, pass FNV0_32_INIT as the
 * Fnv32_t hashval argument to fnv_32_buf() or fnv_32_str().
 *
 * To use the recommended 32 bit FNV-1 hash, pass FNV1_32_INIT as the
 * Fnv32_t hashval argument to fnv_32_buf() or fnv_32_str().
 *
 ***
 *
 * Please do not copyright this code.  This code is in the public domain.
 *
 * LANDON CURT NOLL DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE,
 * INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO
 * EVENT SHALL LANDON CURT NOLL BE LIABLE FOR ANY SPECIAL, INDIRECT OR
 * CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF
 * USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
 * OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
 * PERFORMANCE OF THIS SOFTWARE.
 *
 * By:
 *	chongo <Landon Curt Noll> /\oo/\
 *	http://reality.sgi.com/chongo/
 *	EMail: chongo_fnv at prime dot engr dot sgi dot com
 *
 * Share and Enjoy!	:-)
 */

#include <stdlib.h>
#include "fnv.h"


/* 
 * 32 bit magic FNV-0 and FNV-1 prime 
 */
#define FNV_32_PRIME ((Fnv32_t)0x01000193)


/*
 * fnv_32_buf - perform a 32 bit Fowler/Noll/Vo hash on a buffer
 *
 * input:
 *	buf	- start of buffer to hash
 *	len	- length of buffer in octets
 *	hval	- previous hash value or 0 if first call
 *
 * returns:
 *	32 bit hash as a static hash type
 *
 * NOTE: To use the 32 bit FNV-0 historic hash, use FNV0_32_INIT as the hval
 *	 argument on the first call to either fnv_32_buf() or fnv_32_str().
 *
 * NOTE: To use the recommended 32 bit FNV-1 hash, use FNV1_32_INIT as the hval
 *	 argument on the first call to either fnv_32_buf() or fnv_32_str().
 */
Fnv32_t fnv_32_buf(
    const void *buf,
    size_t len,
    Fnv32_t hval)
{
    const unsigned char *bp = (const unsigned char *) buf;  /* start of buffer */
    const unsigned char *be = bp + len; /* beyond end of buffer */

    /*
     * FNV-1 hash each octet in the buffer
     */
    while (bp < be) {

        /* multiply by the 32 bit FNV magic prime mod 2^64 */
        hval *= FNV_32_PRIME;

        /* xor the bottom with the current octet */
        hval ^= (Fnv32_t) *bp++;
    }

    /* return our new hash value */
    return hval;
}


/*
 * fnv_32_str - perform a 32 bit Fowler/Noll/Vo hash on a string
 *
 * input:
 *	str	- string to hash
 *	hval	- previous hash value or 0 if first call
 *
 * returns:
 *	32 bit hash as a static hash type
 *
 * NOTE: To use the 32 bit FNV-0 historic hash, use FNV0_32_INIT as the hval
 *	 argument on the first call to either fnv_32_buf() or fnv_32_str().
 *
 * NOTE: To use the recommended 32 bit FNV-1 hash, use FNV1_32_INIT as the hval
 *	 argument on the first call to either fnv_32_buf() or fnv_32_str().
 */
Fnv32_t fnv_32_str(
    const char *str,
    Fnv32_t hval)
{
    const unsigned char *s = (const unsigned char *) str;   /* unsigned string */

    /*
     * FNV-1 hash each octet in the buffer
     */
    while (*s) {

        /* multiply by the 32 bit FNV magic prime mod 2^64 */
        hval *= FNV_32_PRIME;

        /* xor the bottom with the current octet */
        hval ^= (Fnv32_t) *s++;
    }

    /* return our new hash value */
    return hval;
}

/* a wrapper function for fnv_32_str */
unsigned long FnvHash( const char *str) {
    return fnv_32_str(str, FNV1_32_INIT);
}