1 /* Licensed to the Apache Software Foundation (ASF) under one or more
2 * contributor license agreements. See the NOTICE file distributed with
3 * this work for additional information regarding copyright ownership.
4 * The ASF licenses this file to You under the Apache License, Version 2.0
5 * (the "License"); you may not use this file except in compliance with
6 * the License. You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17 /*
18 * sdbm - ndbm work-alike hashed database library
19 * based on Per-Aake Larson's Dynamic Hashing algorithms. BIT 18 (1978).
20 * author: oz@nexus.yorku.ca
21 * status: ex-public domain. keep it that way.
22 *
23 * hashing routine
24 */
25
26 #include "apr_sdbm.h"
27 #include "sdbm_private.h"
28
29 /*
30 * polynomial conversion ignoring overflows
31 * [this seems to work remarkably well, in fact better
32 * then the ndbm hash function. Replace at your own risk]
33 * use: 65599 nice.
34 * 65587 even better.
35 */
sdbm_hash(const char * str,int len)36 long sdbm_hash(const char *str, int len)
37 {
38 register unsigned long n = 0;
39
40 #define DUFF /* go ahead and use the loop-unrolled version */
41 #ifdef DUFF
42
43 #define HASHC n = *str++ + 65599 * n
44
45 if (len > 0) {
46 register int loop = (len + 8 - 1) >> 3;
47
48 switch(len & (8 - 1)) {
49 case 0: do {
50 HASHC; case 7: HASHC;
51 case 6: HASHC; case 5: HASHC;
52 case 4: HASHC; case 3: HASHC;
53 case 2: HASHC; case 1: HASHC;
54 } while (--loop);
55 }
56
57 }
58 #else
59 while (len--)
60 n = *str++ + 65599 * n;
61 #endif
62 return n;
63 }
64