1 /*
2 * hash_32 - 32 bit Fowler/Noll/Vo FNV-1a hash code
3 *
4 * @(#) $Revision: 5.1 $
5 * @(#) $Id: hash_32a.c,v 5.1 2009/06/30 09:13:32 chongo Exp $
6 * @(#) $Source: /usr/local/src/cmd/fnv/RCS/hash_32a.c,v $
7 *
8 ***
9 *
10 * Fowler/Noll/Vo hash
11 *
12 * The basis of this hash algorithm was taken from an idea sent
13 * as reviewer comments to the IEEE POSIX P1003.2 committee by:
14 *
15 * Phong Vo (http://www.research.att.com/info/kpv/)
16 * Glenn Fowler (http://www.research.att.com/~gsf/)
17 *
18 * In a subsequent ballot round:
19 *
20 * Landon Curt Noll (http://www.isthe.com/chongo/)
21 *
22 * improved on their algorithm. Some people tried this hash
23 * and found that it worked rather well. In an EMail message
24 * to Landon, they named it the ``Fowler/Noll/Vo'' or FNV hash.
25 *
26 * FNV hashes are designed to be fast while maintaining a low
27 * collision rate. The FNV speed allows one to quickly hash lots
28 * of data while maintaining a reasonable collision rate. See:
29 *
30 * http://www.isthe.com/chongo/tech/comp/fnv/index.html
31 *
32 * for more details as well as other forms of the FNV hash.
33 ***
34 *
35 * To use the recommended 32 bit FNV-1a hash, pass FNV1_32A_INIT as the
36 * Fnv32_t hashval argument to fnv_32a_buf() or fnv_32a_str().
37 *
38 ***
39 *
40 * Please do not copyright this code. This code is in the public domain.
41 *
42 * LANDON CURT NOLL DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE,
43 * INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO
44 * EVENT SHALL LANDON CURT NOLL BE LIABLE FOR ANY SPECIAL, INDIRECT OR
45 * CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF
46 * USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
47 * OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
48 * PERFORMANCE OF THIS SOFTWARE.
49 *
50 * By:
51 * chongo <Landon Curt Noll> /\oo/\
52 * http://www.isthe.com/chongo/
53 *
54 * Share and Enjoy! :-)
55 */
56
57 #include <stdlib.h>
58 #include "fnv.h"
59
60
61 /*
62 * 32 bit magic FNV-1a prime
63 */
64 #define FNV_32_PRIME ((Fnv32_t)0x01000193)
65
66 #if 0
67 /*
68 * fnv_32a_buf - perform a 32 bit Fowler/Noll/Vo FNV-1a hash on a buffer
69 *
70 * input:
71 * buf - start of buffer to hash
72 * len - length of buffer in octets
73 * hval - previous hash value or 0 if first call
74 *
75 * returns:
76 * 32 bit hash as a static hash type
77 *
78 * NOTE: To use the recommended 32 bit FNV-1a hash, use FNV1_32A_INIT as the
79 * hval arg on the first call to either fnv_32a_buf() or fnv_32a_str().
80 */
81 Fnv32_t
82 fnv_32a_buf(void *buf, size_t len, Fnv32_t hval)
83 {
84 unsigned char *bp = (unsigned char *)buf; /* start of buffer */
85 unsigned char *be = bp + len; /* beyond end of buffer */
86
87 /*
88 * FNV-1a hash each octet in the buffer
89 */
90 while (bp < be) {
91
92 /* xor the bottom with the current octet */
93 hval ^= (Fnv32_t)*bp++;
94
95 /* multiply by the 32 bit FNV magic prime mod 2^32 */
96 #if defined(NO_FNV_GCC_OPTIMIZATION)
97 hval *= FNV_32_PRIME;
98 #else
99 hval += (hval<<1) + (hval<<4) + (hval<<7) + (hval<<8) + (hval<<24);
100 #endif
101 }
102
103 /* return our new hash value */
104 return hval;
105 }
106 #endif
107
108
109 /*
110 * fnv_32a_str - perform a 32 bit Fowler/Noll/Vo FNV-1a hash on a string
111 *
112 * input:
113 * str - string to hash
114 * hval - previous hash value or 0 if first call
115 *
116 * returns:
117 * 32 bit hash as a static hash type
118 *
119 * NOTE: To use the recommended 32 bit FNV-1a hash, use FNV1_32A_INIT as the
120 * hval arg on the first call to either fnv_32a_buf() or fnv_32a_str().
121 */
122 Fnv32_t
fnv_32a_str(const char * str,Fnv32_t hval)123 fnv_32a_str(const char *str, Fnv32_t hval)
124 {
125 unsigned const char *s = (unsigned char *)str; /* unsigned string */
126
127 /*
128 * FNV-1a hash each octet in the buffer
129 */
130 while (*s) {
131
132 /* xor the bottom with the current octet */
133 hval ^= (Fnv32_t)*s++;
134
135 /* multiply by the 32 bit FNV magic prime mod 2^32 */
136 #if defined(NO_FNV_GCC_OPTIMIZATION)
137 hval *= FNV_32_PRIME;
138 #else
139 hval += (hval<<1) + (hval<<4) + (hval<<7) + (hval<<8) + (hval<<24);
140 #endif
141 }
142
143 /* return our new hash value */
144 return hval;
145 }
146