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Diffstat (limited to 'lib/fnv/hash_32.c')
| -rw-r--r-- | lib/fnv/hash_32.c | 156 |
1 files changed, 156 insertions, 0 deletions
diff --git a/lib/fnv/hash_32.c b/lib/fnv/hash_32.c new file mode 100644 index 0000000000..077170ff6d --- /dev/null +++ b/lib/fnv/hash_32.c @@ -0,0 +1,156 @@ +/* + * hash_32 - 32 bit Fowler/Noll/Vo hash code + * + * @(#) $Revision: 5.1 $ + * @(#) $Id: hash_32.c,v 5.1 2009/06/30 09:13:32 chongo Exp $ + * @(#) $Source: /usr/local/src/cmd/fnv/RCS/hash_32.c,v $ + * + *** + * + * 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://www.isthe.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 designed 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://www.isthe.com/chongo/tech/comp/fnv/index.html + * + * 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://www.isthe.com/chongo/ + * + * 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(void *buf, size_t len, Fnv32_t hval) +{ + unsigned char *bp = (unsigned char *)buf; /* start of buffer */ + 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 2^32 */ +#if defined(NO_FNV_GCC_OPTIMIZATION) + hval *= FNV_32_PRIME; +#else + hval += (hval<<1) + (hval<<4) + (hval<<7) + (hval<<8) + (hval<<24); +#endif + + /* 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(char *str, Fnv32_t hval) +{ + unsigned char *s = (unsigned char *)str; /* unsigned string */ + + /* + * FNV-1 hash each octet in the buffer + */ + while (*s) { + + /* multiply by the 32 bit FNV magic prime mod 2^32 */ +#if defined(NO_FNV_GCC_OPTIMIZATION) + hval *= FNV_32_PRIME; +#else + hval += (hval<<1) + (hval<<4) + (hval<<7) + (hval<<8) + (hval<<24); +#endif + + /* xor the bottom with the current octet */ + hval ^= (Fnv32_t)*s++; + } + + /* return our new hash value */ + return hval; +} |