8fe3c82b |
1 | /* -*-c-*- |
2 | * |
573eadb5 |
3 | * $Id: unihash.c,v 1.2 2003/12/14 14:45:30 mdw Exp $ |
8fe3c82b |
4 | * |
5 | * Simple and efficient universal hashing for hashtables |
6 | * |
7 | * (c) 2003 Straylight/Edgeware |
8 | */ |
9 | |
10 | /*----- Licensing notice --------------------------------------------------* |
11 | * |
12 | * This file is part of the mLib utilities library. |
13 | * |
14 | * mLib is free software; you can redistribute it and/or modify |
15 | * it under the terms of the GNU Library General Public License as |
16 | * published by the Free Software Foundation; either version 2 of the |
17 | * License, or (at your option) any later version. |
18 | * |
19 | * mLib is distributed in the hope that it will be useful, |
20 | * but WITHOUT ANY WARRANTY; without even the implied warranty of |
21 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
22 | * GNU Library General Public License for more details. |
23 | * |
24 | * You should have received a copy of the GNU Library General Public |
25 | * License along with mLib; if not, write to the Free |
26 | * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, |
27 | * MA 02111-1307, USA. |
28 | */ |
29 | |
30 | /*----- Revision history --------------------------------------------------* |
31 | * |
32 | * $Log: unihash.c,v $ |
573eadb5 |
33 | * Revision 1.2 2003/12/14 14:45:30 mdw |
34 | * Test universal hashing and fix bugs. |
35 | * |
8fe3c82b |
36 | * Revision 1.1 2003/10/12 14:43:24 mdw |
37 | * Universal hashing. |
38 | * |
39 | */ |
40 | |
41 | /*----- Header files ------------------------------------------------------*/ |
42 | |
43 | #include <assert.h> |
44 | #include <stdlib.h> |
45 | |
46 | #include "unihash.h" |
47 | |
48 | /*----- Main code ---------------------------------------------------------*/ |
49 | |
50 | /* --- @unihash_setkey@ --- * |
51 | * |
52 | * Arguments: @unihash_info *i@ = where to store the precomputed tables |
53 | * @uint32 k@ = the key to set, randomly chosen |
54 | * |
55 | * Returns: --- |
56 | * |
57 | * Use: Calculates the tables required for efficient hashing. |
58 | */ |
59 | |
60 | static uint32 mul(uint32 x, uint32 y) |
61 | { |
62 | uint32 z = 0; |
63 | while (y) { |
64 | if (y & 1) z ^= x; |
65 | if (x & (1 << 31)) |
66 | x = U32(x << 1) ^ UNIHASH_POLY; |
67 | else |
68 | x = U32(x << 1); |
69 | y = U32(y >> 1); |
70 | } |
71 | return (z); |
72 | } |
73 | |
74 | void unihash_setkey(unihash_info *i, uint32 k) |
75 | { |
76 | size_t a; |
77 | size_t b; |
78 | uint32 x = 1; |
79 | |
80 | for (a = 0; a < UNIHASH_NBATCH; a++) { |
81 | x = mul(x, k); |
82 | for (b = 0; b < 256; b++) { |
83 | i->s[a][0][b] = mul(x, b << 0); |
84 | i->s[a][1][b] = mul(x, b << 8); |
85 | i->s[a][2][b] = mul(x, b << 16); |
86 | i->s[a][3][b] = mul(x, b << 24); |
87 | } |
88 | } |
89 | } |
90 | |
91 | /* --- @unihash_hash@ --- * |
92 | * |
93 | * Arguments: @const unihash_info *i@ = pointer to precomputed table |
94 | * @uint32 a@ = @i->[0][0][1]@ or value from previous call |
95 | * @const void *p@ = pointer to data to hash |
96 | * @size_t sz@ = size of the data |
97 | * |
573eadb5 |
98 | * Returns: Hash of data so far. |
8fe3c82b |
99 | * |
100 | * Use: Hashes data. Call this as many times as needed. |
101 | */ |
102 | |
103 | uint32 unihash_hash(const unihash_info *i, uint32 a, |
104 | const void *p, size_t sz) |
105 | { |
106 | const octet *pp = p; |
107 | |
108 | assert(UNIHASH_NBATCH == 4); |
109 | |
110 | #define FULLMULT(u, x) \ |
111 | (i->s[u][0][U8((x) >> 0)] ^ i->s[u][1][U8((x) >> 8)] ^ \ |
112 | i->s[u][2][U8((x) >> 16)] ^ i->s[u][3][U8((x) >> 24)]); |
113 | |
114 | #define BYTEMULT(u, x) i->s[u][0][x] |
115 | |
116 | /* --- Do the main bulk in batches of %$n$% bytes --- * |
117 | * |
118 | * We have %$a$% and %$m_{n-1}, \ldots, m_1, m_0$%; we want |
119 | * |
120 | * %$a' = (a + m_{n-1}) k^n + m_{n-2} k^{n-1} + \cdots + m_1 k^2 + m_0 k$% |
121 | */ |
122 | |
123 | while (sz >= UNIHASH_NBATCH) { |
124 | a ^= *pp++; |
125 | a = FULLMULT(3, a); |
126 | a ^= BYTEMULT(2, *pp++); |
127 | a ^= BYTEMULT(1, *pp++); |
128 | a ^= BYTEMULT(0, *pp++); |
573eadb5 |
129 | sz -= UNIHASH_NBATCH; |
8fe3c82b |
130 | } |
131 | |
132 | /* --- The tail end is a smaller batch --- */ |
133 | |
134 | switch (sz) { |
135 | case 3: a ^= *pp++; a = FULLMULT(2, a); goto batch_2; |
136 | case 2: a ^= *pp++; a = FULLMULT(1, a); goto batch_1; |
137 | case 1: a ^= *pp++; a = FULLMULT(0, a); goto batch_0; |
138 | batch_2: a ^= BYTEMULT(1, *pp++); |
139 | batch_1: a ^= BYTEMULT(0, *pp++); |
140 | batch_0: break; |
141 | } |
142 | |
143 | return (a); |
144 | } |
145 | |
146 | /* --- @unihash@ --- * |
147 | * |
148 | * Arguments: @const unihash_info *i@ = precomputed tables |
149 | * @const void *p@ = pointer to data to hash |
150 | * @size_t sz@ = size of the data |
151 | * |
152 | * Returns: The hash value computed. |
153 | * |
154 | * Use: All-in-one hashing function. No faster than using the |
155 | * separate calls, but more convenient. |
156 | */ |
157 | |
158 | uint32 unihash(const unihash_info *i, const void *p, size_t sz) |
159 | { |
160 | return (UNIHASH(i, p, sz)); |
161 | } |
162 | |
573eadb5 |
163 | /*----- Test rig ----------------------------------------------------------*/ |
164 | |
165 | #ifdef TEST_RIG |
166 | |
167 | #include "testrig.h" |
168 | |
169 | static int verify(dstr *v) |
170 | { |
171 | unihash_info ui; |
172 | uint32 k; |
173 | uint32 h, hh; |
174 | size_t n; |
175 | int i, c; |
176 | const char *p; |
177 | int ok = 1; |
178 | |
179 | static const int step[] = { 0, 1, 5, 6, 7, 8, 23, -1 }; |
180 | |
181 | /* --- Set up for using this key --- */ |
182 | |
183 | k = *(uint32 *)v[0].buf; |
184 | h = *(uint32 *)v[2].buf; |
185 | unihash_setkey(&ui, k); |
186 | |
187 | /* --- Hash the data a lot --- */ |
188 | |
189 | for (i = 0; step[i] >= 0; i++) { |
190 | c = step[i]; |
191 | if (!c) |
192 | hh = unihash(&ui, v[1].buf, v[1].len); |
193 | else { |
194 | hh = UNIHASH_INIT(&ui); |
195 | p = v[1].buf; |
196 | n = v[1].len; |
197 | while (n) { |
198 | if (c > n) c = n; |
199 | hh = unihash_hash(&ui, hh, p, c); |
200 | p += c; |
201 | n -= c; |
202 | } |
203 | } |
204 | if (h != hh) { |
205 | ok = 0; |
206 | fprintf(stderr, "\nunihash failed\n"); |
207 | fprintf(stderr, " key = %08lx\n", (unsigned long)k); |
208 | fprintf(stderr, " data = %s\n", v[1].buf); |
209 | fprintf(stderr, " step = %d\n", step[i]); |
210 | fprintf(stderr, " expected = %08lx\n", (unsigned long)h); |
211 | fprintf(stderr, " computed = %08lx\n", (unsigned long)hh); |
212 | } |
213 | } |
214 | return (ok); |
215 | } |
216 | |
217 | static const test_chunk tests[] = { |
218 | { "hash", verify, { &type_uint32, &type_string, &type_uint32 } }, |
219 | { 0, 0, { 0 } } |
220 | }; |
221 | |
222 | int main(int argc, char *argv[]) |
223 | { |
224 | test_run(argc, argv, tests, "unihash.in"); |
225 | return (0); |
226 | } |
227 | |
228 | #endif |
229 | |
8fe3c82b |
230 | /*----- That's all, folks -------------------------------------------------*/ |