hash_func.c revision 1574 
1/*-
2 * Copyright (c) 1990, 1993
3 *	The Regents of the University of California.  All rights reserved.
4 *
5 * This code is derived from software contributed to Berkeley by
6 * Margo Seltzer.
7 *
8 * Redistribution and use in source and binary forms, with or without
9 * modification, are permitted provided that the following conditions
10 * are met:
11 * 1. Redistributions of source code must retain the above copyright
12 *    notice, this list of conditions and the following disclaimer.
13 * 2. Redistributions in binary form must reproduce the above copyright
14 *    notice, this list of conditions and the following disclaimer in the
15 *    documentation and/or other materials provided with the distribution.
16 * 3. All advertising materials mentioning features or use of this software
17 *    must display the following acknowledgement:
18 *	This product includes software developed by the University of
19 *	California, Berkeley and its contributors.
20 * 4. Neither the name of the University nor the names of its contributors
21 *    may be used to endorse or promote products derived from this software
22 *    without specific prior written permission.
23 *
24 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
25 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
26 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
27 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
28 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
29 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
30 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
31 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
32 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
33 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
34 * SUCH DAMAGE.
35 */
36
37#if defined(LIBC_SCCS) && !defined(lint)
38static char sccsid[] = "@(#)hash_func.c	8.2 (Berkeley) 2/21/94";
39#endif /* LIBC_SCCS and not lint */
40
41#include <sys/types.h>
42
43#include <db.h>
44#include "hash.h"
45#include "page.h"
46#include "extern.h"
47
48static u_int32_t hash1 __P((const void *, size_t));
49static u_int32_t hash2 __P((const void *, size_t));
50static u_int32_t hash3 __P((const void *, size_t));
51static u_int32_t hash4 __P((const void *, size_t));
52
53/* Global default hash function */
54u_int32_t (*__default_hash) __P((const void *, size_t)) = hash4;
55
56/*
57 * HASH FUNCTIONS
58 *
59 * Assume that we've already split the bucket to which this key hashes,
60 * calculate that bucket, and check that in fact we did already split it.
61 *
62 * This came from ejb's hsearch.
63 */
64
65#define PRIME1		37
66#define PRIME2		1048583
67
68static u_int32_t
69hash1(keyarg, len)
70	const void *keyarg;
71	register size_t len;
72{
73	register const u_char *key;
74	register u_int32_t h;
75
76	/* Convert string to integer */
77	for (key = keyarg, h = 0; len--;)
78		h = h * PRIME1 ^ (*key++ - ' ');
79	h %= PRIME2;
80	return (h);
81}
82
83/*
84 * Phong's linear congruential hash
85 */
86#define dcharhash(h, c)	((h) = 0x63c63cd9*(h) + 0x9c39c33d + (c))
87
88static u_int32_t
89hash2(keyarg, len)
90	const void *keyarg;
91	size_t len;
92{
93	register const u_char *e, *key;
94	register u_int32_t h;
95	register u_char c;
96
97	key = keyarg;
98	e = key + len;
99	for (h = 0; key != e;) {
100		c = *key++;
101		if (!c && key > e)
102			break;
103		dcharhash(h, c);
104	}
105	return (h);
106}
107
108/*
109 * This is INCREDIBLY ugly, but fast.  We break the string up into 8 byte
110 * units.  On the first time through the loop we get the "leftover bytes"
111 * (strlen % 8).  On every other iteration, we perform 8 HASHC's so we handle
112 * all 8 bytes.  Essentially, this saves us 7 cmp & branch instructions.  If
113 * this routine is heavily used enough, it's worth the ugly coding.
114 *
115 * OZ's original sdbm hash
116 */
117static u_int32_t
118hash3(keyarg, len)
119	const void *keyarg;
120	register size_t len;
121{
122	register const u_char *key;
123	register size_t loop;
124	register u_int32_t h;
125
126#define HASHC   h = *key++ + 65599 * h
127
128	h = 0;
129	key = keyarg;
130	if (len > 0) {
131		loop = (len + 8 - 1) >> 3;
132
133		switch (len & (8 - 1)) {
134		case 0:
135			do {
136				HASHC;
137				/* FALLTHROUGH */
138		case 7:
139				HASHC;
140				/* FALLTHROUGH */
141		case 6:
142				HASHC;
143				/* FALLTHROUGH */
144		case 5:
145				HASHC;
146				/* FALLTHROUGH */
147		case 4:
148				HASHC;
149				/* FALLTHROUGH */
150		case 3:
151				HASHC;
152				/* FALLTHROUGH */
153		case 2:
154				HASHC;
155				/* FALLTHROUGH */
156		case 1:
157				HASHC;
158			} while (--loop);
159		}
160	}
161	return (h);
162}
163
164/* Hash function from Chris Torek. */
165static u_int32_t
166hash4(keyarg, len)
167	const void *keyarg;
168	register size_t len;
169{
170	register const u_char *key;
171	register size_t loop;
172	register u_int32_t h;
173
174#define HASH4a   h = (h << 5) - h + *key++;
175#define HASH4b   h = (h << 5) + h + *key++;
176#define HASH4 HASH4b
177
178	h = 0;
179	key = keyarg;
180	if (len > 0) {
181		loop = (len + 8 - 1) >> 3;
182
183		switch (len & (8 - 1)) {
184		case 0:
185			do {
186				HASH4;
187				/* FALLTHROUGH */
188		case 7:
189				HASH4;
190				/* FALLTHROUGH */
191		case 6:
192				HASH4;
193				/* FALLTHROUGH */
194		case 5:
195				HASH4;
196				/* FALLTHROUGH */
197		case 4:
198				HASH4;
199				/* FALLTHROUGH */
200		case 3:
201				HASH4;
202				/* FALLTHROUGH */
203		case 2:
204				HASH4;
205				/* FALLTHROUGH */
206		case 1:
207				HASH4;
208			} while (--loop);
209		}
210	}
211	return (h);
212}
213