hash.c revision 1.3 
1/*	$NetBSD: hash.c,v 1.3 2019/01/09 16:55:14 christos Exp $	*/
2
3/*
4 * Copyright (C) Internet Systems Consortium, Inc. ("ISC")
5 *
6 * This Source Code Form is subject to the terms of the Mozilla Public
7 * License, v. 2.0. If a copy of the MPL was not distributed with this
8 * file, You can obtain one at http://mozilla.org/MPL/2.0/.
9 *
10 * See the COPYRIGHT file distributed with this work for additional
11 * information regarding copyright ownership.
12 */
13
14/*
15 * 32 bit Fowler/Noll/Vo FNV-1a hash code with modification for BIND
16 */
17
18#include <config.h> // IWYU pragma: keep
19
20#include <stdbool.h>
21#include <stddef.h>
22#include <inttypes.h>
23
24#include "isc/hash.h" // IWYU pragma: keep
25#include "isc/likely.h"
26#include "isc/once.h"
27#include "isc/random.h"
28#include "isc/result.h"
29#include "isc/types.h"
30#include "isc/util.h"
31
32static uint32_t fnv_offset_basis;
33static isc_once_t fnv_once = ISC_ONCE_INIT;
34static bool fnv_initialized = false;
35
36static unsigned char maptolower[] = {
37	0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07,
38	0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f,
39	0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17,
40	0x18, 0x19, 0x1a, 0x1b, 0x1c, 0x1d, 0x1e, 0x1f,
41	0x20, 0x21, 0x22, 0x23, 0x24, 0x25, 0x26, 0x27,
42	0x28, 0x29, 0x2a, 0x2b, 0x2c, 0x2d, 0x2e, 0x2f,
43	0x30, 0x31, 0x32, 0x33, 0x34, 0x35, 0x36, 0x37,
44	0x38, 0x39, 0x3a, 0x3b, 0x3c, 0x3d, 0x3e, 0x3f,
45	0x40, 0x61, 0x62, 0x63, 0x64, 0x65, 0x66, 0x67,
46	0x68, 0x69, 0x6a, 0x6b, 0x6c, 0x6d, 0x6e, 0x6f,
47	0x70, 0x71, 0x72, 0x73, 0x74, 0x75, 0x76, 0x77,
48	0x78, 0x79, 0x7a, 0x5b, 0x5c, 0x5d, 0x5e, 0x5f,
49	0x60, 0x61, 0x62, 0x63, 0x64, 0x65, 0x66, 0x67,
50	0x68, 0x69, 0x6a, 0x6b, 0x6c, 0x6d, 0x6e, 0x6f,
51	0x70, 0x71, 0x72, 0x73, 0x74, 0x75, 0x76, 0x77,
52	0x78, 0x79, 0x7a, 0x7b, 0x7c, 0x7d, 0x7e, 0x7f,
53	0x80, 0x81, 0x82, 0x83, 0x84, 0x85, 0x86, 0x87,
54	0x88, 0x89, 0x8a, 0x8b, 0x8c, 0x8d, 0x8e, 0x8f,
55	0x90, 0x91, 0x92, 0x93, 0x94, 0x95, 0x96, 0x97,
56	0x98, 0x99, 0x9a, 0x9b, 0x9c, 0x9d, 0x9e, 0x9f,
57	0xa0, 0xa1, 0xa2, 0xa3, 0xa4, 0xa5, 0xa6, 0xa7,
58	0xa8, 0xa9, 0xaa, 0xab, 0xac, 0xad, 0xae, 0xaf,
59	0xb0, 0xb1, 0xb2, 0xb3, 0xb4, 0xb5, 0xb6, 0xb7,
60	0xb8, 0xb9, 0xba, 0xbb, 0xbc, 0xbd, 0xbe, 0xbf,
61	0xc0, 0xc1, 0xc2, 0xc3, 0xc4, 0xc5, 0xc6, 0xc7,
62	0xc8, 0xc9, 0xca, 0xcb, 0xcc, 0xcd, 0xce, 0xcf,
63	0xd0, 0xd1, 0xd2, 0xd3, 0xd4, 0xd5, 0xd6, 0xd7,
64	0xd8, 0xd9, 0xda, 0xdb, 0xdc, 0xdd, 0xde, 0xdf,
65	0xe0, 0xe1, 0xe2, 0xe3, 0xe4, 0xe5, 0xe6, 0xe7,
66	0xe8, 0xe9, 0xea, 0xeb, 0xec, 0xed, 0xee, 0xef,
67	0xf0, 0xf1, 0xf2, 0xf3, 0xf4, 0xf5, 0xf6, 0xf7,
68	0xf8, 0xf9, 0xfa, 0xfb, 0xfc, 0xfd, 0xfe, 0xff
69};
70
71static void
72fnv_initialize(void) {
73	/*
74	 * This function should not leave fnv_offset_basis set to
75	 * 0. Also, after this function has been called, if it is called
76	 * again, it should not change fnv_offset_basis.
77	 */
78	while (fnv_offset_basis == 0) {
79		fnv_offset_basis = isc_random32();
80	}
81
82	fnv_initialized = true;
83}
84
85const void *
86isc_hash_get_initializer(void) {
87	if (ISC_UNLIKELY(!fnv_initialized))
88		RUNTIME_CHECK(isc_once_do(&fnv_once, fnv_initialize) ==
89			      ISC_R_SUCCESS);
90
91	return (&fnv_offset_basis);
92}
93
94void
95isc_hash_set_initializer(const void *initializer) {
96	REQUIRE(initializer != NULL);
97
98	/*
99	 * Ensure that fnv_initialize() is not called after
100	 * isc_hash_set_initializer() is called.
101	 */
102	if (ISC_UNLIKELY(!fnv_initialized))
103		RUNTIME_CHECK(isc_once_do(&fnv_once, fnv_initialize) ==
104			      ISC_R_SUCCESS);
105
106	fnv_offset_basis = *((const unsigned int *)initializer);
107}
108
109#define FNV_32_PRIME ((uint32_t)0x01000193)
110
111uint32_t
112isc_hash_function(const void *data, size_t length, bool case_sensitive,
113		  const uint32_t *previous_hashp)
114{
115	uint32_t hval;
116	const unsigned char *bp;
117	const unsigned char *be;
118
119	REQUIRE(length == 0 || data != NULL);
120
121	if (ISC_UNLIKELY(!fnv_initialized)) {
122		RUNTIME_CHECK(isc_once_do(&fnv_once, fnv_initialize) ==
123			      ISC_R_SUCCESS);
124	}
125
126	hval = ISC_UNLIKELY(previous_hashp != NULL) ? *previous_hashp
127						    : fnv_offset_basis;
128
129	if (length == 0) {
130		return (hval);
131	}
132
133	bp = (const unsigned char *)data;
134	be = bp + length;
135
136	/*
137	 * Fowler-Noll-Vo FNV-1a hash function.
138	 *
139	 * NOTE: A random FNV offset basis is used by default to avoid
140	 * collision attacks as the hash function is reversible. This
141	 * makes the mapping non-deterministic, but the distribution in
142	 * the domain is still uniform.
143	 */
144
145	if (case_sensitive) {
146		while (bp < be) {
147			hval ^= *bp++;
148			hval *= FNV_32_PRIME;
149		}
150	} else {
151		while (bp < be) {
152			hval ^= maptolower[*bp++];
153			hval *= FNV_32_PRIME;
154		}
155	}
156
157	return (hval);
158}
159
160uint32_t
161isc_hash_function_reverse(const void *data, size_t length, bool case_sensitive,
162			  const uint32_t *previous_hashp)
163{
164	uint32_t hval;
165	const unsigned char *bp;
166	const unsigned char *be;
167
168	REQUIRE(length == 0 || data != NULL);
169
170	if (ISC_UNLIKELY(!fnv_initialized)) {
171		RUNTIME_CHECK(isc_once_do(&fnv_once, fnv_initialize) ==
172			      ISC_R_SUCCESS);
173	}
174
175	hval = ISC_UNLIKELY(previous_hashp != NULL) ? *previous_hashp
176						    : fnv_offset_basis;
177
178	if (length == 0) {
179		return (hval);
180	}
181
182	bp = (const unsigned char *)data;
183	be = bp + length;
184
185	/*
186	 * Fowler-Noll-Vo FNV-1a hash function.
187	 *
188	 * NOTE: A random FNV offset basis is used by default to avoid
189	 * collision attacks as the hash function is reversible. This
190	 * makes the mapping non-deterministic, but the distribution in
191	 * the domain is still uniform.
192	 */
193
194	if (case_sensitive) {
195		while (--be >= bp) {
196			hval ^= *be;
197			hval *= FNV_32_PRIME;
198		}
199	} else {
200		while (--be >= bp) {
201			hval ^= maptolower[*be];
202			hval *= FNV_32_PRIME;
203		}
204	}
205
206	return (hval);
207}
208