155 lines
4.3 KiB
C
155 lines
4.3 KiB
C
/*
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* hash_32 - 32 bit Fowler/Noll/Vo hash code
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*
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*
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***
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*
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* Fowler/Noll/Vo hash
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*
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* The basis of this hash algorithm was taken from an idea sent
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* as reviewer comments to the IEEE POSIX P1003.2 committee by:
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*
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* Phong Vo (http://www.research.att.com/info/kpv/)
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* Glenn Fowler (http://www.research.att.com/~gsf/)
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*
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* In a subsequent ballot round:
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*
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* Landon Curt Noll (http://reality.sgi.com/chongo/)
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*
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* improved on their algorithm. Some people tried this hash
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* and found that it worked rather well. In an EMail message
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* to Landon, they named it the ``Fowler/Noll/Vo'' or FNV hash.
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*
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* FNV hashes are architected to be fast while maintaining a low
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* collision rate. The FNV speed allows one to quickly hash lots
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* of data while maintaining a reasonable collision rate. See:
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*
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* http://reality.sgi.com/chongo/tech/comp/fnv/
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*
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* for more details as well as other forms of the FNV hash.
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***
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*
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* NOTE: The FNV-0 historic hash is not recommended. One should use
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* the FNV-1 hash instead.
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*
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* To use the 32 bit FNV-0 historic hash, pass FNV0_32_INIT as the
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* Fnv32_t hashval argument to fnv_32_buf() or fnv_32_str().
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*
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* To use the recommended 32 bit FNV-1 hash, pass FNV1_32_INIT as the
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* Fnv32_t hashval argument to fnv_32_buf() or fnv_32_str().
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*
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***
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*
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* Please do not copyright this code. This code is in the public domain.
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*
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* LANDON CURT NOLL DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE,
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* INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO
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* EVENT SHALL LANDON CURT NOLL BE LIABLE FOR ANY SPECIAL, INDIRECT OR
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* CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF
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* USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
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* OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
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* PERFORMANCE OF THIS SOFTWARE.
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*
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* By:
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* chongo <Landon Curt Noll> /\oo/\
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* http://reality.sgi.com/chongo/
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* EMail: chongo_fnv at prime dot engr dot sgi dot com
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*
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* Share and Enjoy! :-)
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*/
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#include <stdlib.h>
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#include "fnv.h"
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/*
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* 32 bit magic FNV-0 and FNV-1 prime
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*/
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#define FNV_32_PRIME ((Fnv32_t)0x01000193)
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/*
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* fnv_32_buf - perform a 32 bit Fowler/Noll/Vo hash on a buffer
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*
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* input:
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* buf - start of buffer to hash
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* len - length of buffer in octets
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* hval - previous hash value or 0 if first call
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*
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* returns:
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* 32 bit hash as a static hash type
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*
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* NOTE: To use the 32 bit FNV-0 historic hash, use FNV0_32_INIT as the hval
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* argument on the first call to either fnv_32_buf() or fnv_32_str().
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*
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* NOTE: To use the recommended 32 bit FNV-1 hash, use FNV1_32_INIT as the hval
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* argument on the first call to either fnv_32_buf() or fnv_32_str().
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*/
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Fnv32_t fnv_32_buf(
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const void *buf,
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size_t len,
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Fnv32_t hval)
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{
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const unsigned char *bp = (const unsigned char *) buf; /* start of buffer */
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const unsigned char *be = bp + len; /* beyond end of buffer */
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/*
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* FNV-1 hash each octet in the buffer
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*/
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while (bp < be) {
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/* multiply by the 32 bit FNV magic prime mod 2^64 */
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hval *= FNV_32_PRIME;
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/* xor the bottom with the current octet */
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hval ^= (Fnv32_t) *bp++;
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}
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/* return our new hash value */
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return hval;
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}
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/*
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* fnv_32_str - perform a 32 bit Fowler/Noll/Vo hash on a string
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*
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* input:
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* str - string to hash
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* hval - previous hash value or 0 if first call
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*
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* returns:
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* 32 bit hash as a static hash type
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*
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* NOTE: To use the 32 bit FNV-0 historic hash, use FNV0_32_INIT as the hval
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* argument on the first call to either fnv_32_buf() or fnv_32_str().
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*
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* NOTE: To use the recommended 32 bit FNV-1 hash, use FNV1_32_INIT as the hval
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* argument on the first call to either fnv_32_buf() or fnv_32_str().
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*/
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Fnv32_t fnv_32_str(
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const char *str,
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Fnv32_t hval)
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{
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const unsigned char *s = (const unsigned char *) str; /* unsigned string */
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/*
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* FNV-1 hash each octet in the buffer
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*/
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while (*s) {
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/* multiply by the 32 bit FNV magic prime mod 2^64 */
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hval *= FNV_32_PRIME;
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/* xor the bottom with the current octet */
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hval ^= (Fnv32_t) *s++;
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}
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/* return our new hash value */
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return hval;
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}
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/* a wrapper function for fnv_32_str */
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unsigned long FnvHash( const char *str) {
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return fnv_32_str(str, FNV1_32_INIT);
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}
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