1/*-
2 * SPDX-License-Identifier: BSD-3-Clause
3 *
4 * Copyright (c) 1990, 1993
5 *	The Regents of the University of California.  All rights reserved.
6 *
7 * This code is derived from software contributed to Berkeley by
8 * Margo Seltzer.
9 *
10 * Redistribution and use in source and binary forms, with or without
11 * modification, are permitted provided that the following conditions
12 * are met:
13 * 1. Redistributions of source code must retain the above copyright
14 *    notice, this list of conditions and the following disclaimer.
15 * 2. Redistributions in binary form must reproduce the above copyright
16 *    notice, this list of conditions and the following disclaimer in the
17 *    documentation and/or other materials provided with the distribution.
18 * 3. Neither the name of the University nor the names of its contributors
19 *    may be used to endorse or promote products derived from this software
20 *    without specific prior written permission.
21 *
22 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
23 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
24 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
25 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
26 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
27 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
28 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
29 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
30 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
31 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
32 * SUCH DAMAGE.
33 */
34
35#if defined(LIBC_SCCS) && !defined(lint)
36static char sccsid[] = "@(#)hash_func.c	8.2 (Berkeley) 2/21/94";
37#endif /* LIBC_SCCS and not lint */
38#include <sys/cdefs.h>
39__FBSDID("$FreeBSD$");
40
41#include <sys/types.h>
42
43#include <db.h>
44#include "hash.h"
45#include "page.h"
46#include "extern.h"
47
48#ifdef notdef
49static u_int32_t hash1(const void *, size_t) __unused;
50static u_int32_t hash2(const void *, size_t) __unused;
51static u_int32_t hash3(const void *, size_t) __unused;
52#endif
53static u_int32_t hash4(const void *, size_t);
54
55/* Default hash function. */
56u_int32_t (*__default_hash)(const void *, size_t) = hash4;
57
58#ifdef notdef
59/*
60 * Assume that we've already split the bucket to which this key hashes,
61 * calculate that bucket, and check that in fact we did already split it.
62 *
63 * EJB's original hsearch hash.
64 */
65#define PRIME1		37
66#define PRIME2		1048583
67
68u_int32_t
69hash1(const void *key, size_t len)
70{
71	u_int32_t h;
72	u_int8_t *k;
73
74	h = 0;
75	k = (u_int8_t *)key;
76	/* Convert string to integer */
77	while (len--)
78		h = h * PRIME1 ^ (*k++ - ' ');
79	h %= PRIME2;
80	return (h);
81}
82
83/*
84 * Phong Vo's linear congruential hash
85 */
86#define dcharhash(h, c)	((h) = 0x63c63cd9*(h) + 0x9c39c33d + (c))
87
88u_int32_t
89hash2(const void *key, size_t len)
90{
91	u_int32_t h;
92	u_int8_t *e, c, *k;
93
94	k = (u_int8_t *)key;
95	e = k + len;
96	for (h = 0; k != e;) {
97		c = *k++;
98		if (!c && k > e)
99			break;
100		dcharhash(h, c);
101	}
102	return (h);
103}
104
105/*
106 * This is INCREDIBLY ugly, but fast.  We break the string up into 8 byte
107 * units.  On the first time through the loop we get the "leftover bytes"
108 * (strlen % 8).  On every other iteration, we perform 8 HASHC's so we handle
109 * all 8 bytes.  Essentially, this saves us 7 cmp & branch instructions.  If
110 * this routine is heavily used enough, it's worth the ugly coding.
111 *
112 * Ozan Yigit's original sdbm hash.
113 */
114u_int32_t
115hash3(const void *key, size_t len)
116{
117	u_int32_t n, loop;
118	u_int8_t *k;
119
120#define HASHC   n = *k++ + 65599 * n
121
122	n = 0;
123	k = (u_int8_t *)key;
124	if (len > 0) {
125		loop = (len + 8 - 1) >> 3;
126
127		switch (len & (8 - 1)) {
128		case 0:
129			do {	/* All fall throughs */
130				HASHC;
131		case 7:
132				HASHC;
133		case 6:
134				HASHC;
135		case 5:
136				HASHC;
137		case 4:
138				HASHC;
139		case 3:
140				HASHC;
141		case 2:
142				HASHC;
143		case 1:
144				HASHC;
145			} while (--loop);
146		}
147
148	}
149	return (n);
150}
151#endif /* notdef */
152
153/* Chris Torek's hash function. */
154u_int32_t
155hash4(const void *key, size_t len)
156{
157	u_int32_t h, loop;
158	const u_int8_t *k;
159
160#define HASH4a   h = (h << 5) - h + *k++;
161#define HASH4b   h = (h << 5) + h + *k++;
162#define HASH4 HASH4b
163
164	h = 0;
165	k = key;
166	if (len > 0) {
167		loop = (len + 8 - 1) >> 3;
168
169		switch (len & (8 - 1)) {
170		case 0:
171			do {	/* All fall throughs */
172				HASH4;
173		case 7:
174				HASH4;
175		case 6:
176				HASH4;
177		case 5:
178				HASH4;
179		case 4:
180				HASH4;
181		case 3:
182				HASH4;
183		case 2:
184				HASH4;
185		case 1:
186				HASH4;
187			} while (--loop);
188		}
189
190	}
191	return (h);
192}
193