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 * 4. Neither the name of the University nor the names of its contributors
17 *    may be used to endorse or promote products derived from this software
18 *    without specific prior written permission.
19 *
20 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
21 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
22 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
23 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
24 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
25 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
26 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
27 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
28 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
29 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
30 * SUCH DAMAGE.
31 */
32
33#if defined(LIBC_SCCS) && !defined(lint)
34static char sccsid[] = "@(#)hash_func.c	8.2 (Berkeley) 2/21/94";
35#endif /* LIBC_SCCS and not lint */
36#include <sys/cdefs.h>
37__FBSDID("$FreeBSD$");
38
39#include <sys/types.h>
40
41#include <db.h>
42#include "hash.h"
43#include "page.h"
44#include "extern.h"
45
46#ifdef notdef
47static u_int32_t hash1(const void *, size_t) __unused;
48static u_int32_t hash2(const void *, size_t) __unused;
49static u_int32_t hash3(const void *, size_t) __unused;
50#endif
51static u_int32_t hash4(const void *, size_t);
52
53/* Default hash function. */
54u_int32_t (*__default_hash)(const void *, size_t) = hash4;
55
56#ifdef notdef
57/*
58 * Assume that we've already split the bucket to which this key hashes,
59 * calculate that bucket, and check that in fact we did already split it.
60 *
61 * EJB's original hsearch hash.
62 */
63#define PRIME1		37
64#define PRIME2		1048583
65
66u_int32_t
67hash1(const void *key, size_t len)
68{
69	u_int32_t h;
70	u_int8_t *k;
71
72	h = 0;
73	k = (u_int8_t *)key;
74	/* Convert string to integer */
75	while (len--)
76		h = h * PRIME1 ^ (*k++ - ' ');
77	h %= PRIME2;
78	return (h);
79}
80
81/*
82 * Phong Vo's linear congruential hash
83 */
84#define dcharhash(h, c)	((h) = 0x63c63cd9*(h) + 0x9c39c33d + (c))
85
86u_int32_t
87hash2(const void *key, size_t len)
88{
89	u_int32_t h;
90	u_int8_t *e, c, *k;
91
92	k = (u_int8_t *)key;
93	e = k + len;
94	for (h = 0; k != e;) {
95		c = *k++;
96		if (!c && k > e)
97			break;
98		dcharhash(h, c);
99	}
100	return (h);
101}
102
103/*
104 * This is INCREDIBLY ugly, but fast.  We break the string up into 8 byte
105 * units.  On the first time through the loop we get the "leftover bytes"
106 * (strlen % 8).  On every other iteration, we perform 8 HASHC's so we handle
107 * all 8 bytes.  Essentially, this saves us 7 cmp & branch instructions.  If
108 * this routine is heavily used enough, it's worth the ugly coding.
109 *
110 * Ozan Yigit's original sdbm hash.
111 */
112u_int32_t
113hash3(const void *key, size_t len)
114{
115	u_int32_t n, loop;
116	u_int8_t *k;
117
118#define HASHC   n = *k++ + 65599 * n
119
120	n = 0;
121	k = (u_int8_t *)key;
122	if (len > 0) {
123		loop = (len + 8 - 1) >> 3;
124
125		switch (len & (8 - 1)) {
126		case 0:
127			do {	/* All fall throughs */
128				HASHC;
129		case 7:
130				HASHC;
131		case 6:
132				HASHC;
133		case 5:
134				HASHC;
135		case 4:
136				HASHC;
137		case 3:
138				HASHC;
139		case 2:
140				HASHC;
141		case 1:
142				HASHC;
143			} while (--loop);
144		}
145
146	}
147	return (n);
148}
149#endif /* notdef */
150
151/* Chris Torek's hash function. */
152u_int32_t
153hash4(const void *key, size_t len)
154{
155	u_int32_t h, loop;
156	const u_int8_t *k;
157
158#define HASH4a   h = (h << 5) - h + *k++;
159#define HASH4b   h = (h << 5) + h + *k++;
160#define HASH4 HASH4b
161
162	h = 0;
163	k = key;
164	if (len > 0) {
165		loop = (len + 8 - 1) >> 3;
166
167		switch (len & (8 - 1)) {
168		case 0:
169			do {	/* All fall throughs */
170				HASH4;
171		case 7:
172				HASH4;
173		case 6:
174				HASH4;
175		case 5:
176				HASH4;
177		case 4:
178				HASH4;
179		case 3:
180				HASH4;
181		case 2:
182				HASH4;
183		case 1:
184				HASH4;
185			} while (--loop);
186		}
187
188	}
189	return (h);
190}
191