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1 | /* -*-c-*- |
2 | * |
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3 | * $Id: unihash.c,v 1.3 2004/04/08 01:36:13 mdw Exp $ |
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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 | |
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30 | /*----- Header files ------------------------------------------------------*/ |
31 | |
32 | #include <assert.h> |
33 | #include <stdlib.h> |
34 | |
35 | #include "unihash.h" |
36 | |
37 | /*----- Main code ---------------------------------------------------------*/ |
38 | |
39 | /* --- @unihash_setkey@ --- * |
40 | * |
41 | * Arguments: @unihash_info *i@ = where to store the precomputed tables |
42 | * @uint32 k@ = the key to set, randomly chosen |
43 | * |
44 | * Returns: --- |
45 | * |
46 | * Use: Calculates the tables required for efficient hashing. |
47 | */ |
48 | |
49 | static uint32 mul(uint32 x, uint32 y) |
50 | { |
51 | uint32 z = 0; |
52 | while (y) { |
53 | if (y & 1) z ^= x; |
54 | if (x & (1 << 31)) |
55 | x = U32(x << 1) ^ UNIHASH_POLY; |
56 | else |
57 | x = U32(x << 1); |
58 | y = U32(y >> 1); |
59 | } |
60 | return (z); |
61 | } |
62 | |
63 | void unihash_setkey(unihash_info *i, uint32 k) |
64 | { |
65 | size_t a; |
66 | size_t b; |
67 | uint32 x = 1; |
68 | |
69 | for (a = 0; a < UNIHASH_NBATCH; a++) { |
70 | x = mul(x, k); |
71 | for (b = 0; b < 256; b++) { |
72 | i->s[a][0][b] = mul(x, b << 0); |
73 | i->s[a][1][b] = mul(x, b << 8); |
74 | i->s[a][2][b] = mul(x, b << 16); |
75 | i->s[a][3][b] = mul(x, b << 24); |
76 | } |
77 | } |
78 | } |
79 | |
80 | /* --- @unihash_hash@ --- * |
81 | * |
82 | * Arguments: @const unihash_info *i@ = pointer to precomputed table |
83 | * @uint32 a@ = @i->[0][0][1]@ or value from previous call |
84 | * @const void *p@ = pointer to data to hash |
85 | * @size_t sz@ = size of the data |
86 | * |
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87 | * Returns: Hash of data so far. |
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88 | * |
89 | * Use: Hashes data. Call this as many times as needed. |
90 | */ |
91 | |
92 | uint32 unihash_hash(const unihash_info *i, uint32 a, |
93 | const void *p, size_t sz) |
94 | { |
95 | const octet *pp = p; |
96 | |
97 | assert(UNIHASH_NBATCH == 4); |
98 | |
99 | #define FULLMULT(u, x) \ |
100 | (i->s[u][0][U8((x) >> 0)] ^ i->s[u][1][U8((x) >> 8)] ^ \ |
101 | i->s[u][2][U8((x) >> 16)] ^ i->s[u][3][U8((x) >> 24)]); |
102 | |
103 | #define BYTEMULT(u, x) i->s[u][0][x] |
104 | |
105 | /* --- Do the main bulk in batches of %$n$% bytes --- * |
106 | * |
107 | * We have %$a$% and %$m_{n-1}, \ldots, m_1, m_0$%; we want |
108 | * |
109 | * %$a' = (a + m_{n-1}) k^n + m_{n-2} k^{n-1} + \cdots + m_1 k^2 + m_0 k$% |
110 | */ |
111 | |
112 | while (sz >= UNIHASH_NBATCH) { |
113 | a ^= *pp++; |
114 | a = FULLMULT(3, a); |
115 | a ^= BYTEMULT(2, *pp++); |
116 | a ^= BYTEMULT(1, *pp++); |
117 | a ^= BYTEMULT(0, *pp++); |
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118 | sz -= UNIHASH_NBATCH; |
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119 | } |
120 | |
121 | /* --- The tail end is a smaller batch --- */ |
122 | |
123 | switch (sz) { |
124 | case 3: a ^= *pp++; a = FULLMULT(2, a); goto batch_2; |
125 | case 2: a ^= *pp++; a = FULLMULT(1, a); goto batch_1; |
126 | case 1: a ^= *pp++; a = FULLMULT(0, a); goto batch_0; |
127 | batch_2: a ^= BYTEMULT(1, *pp++); |
128 | batch_1: a ^= BYTEMULT(0, *pp++); |
129 | batch_0: break; |
130 | } |
131 | |
132 | return (a); |
133 | } |
134 | |
135 | /* --- @unihash@ --- * |
136 | * |
137 | * Arguments: @const unihash_info *i@ = precomputed tables |
138 | * @const void *p@ = pointer to data to hash |
139 | * @size_t sz@ = size of the data |
140 | * |
141 | * Returns: The hash value computed. |
142 | * |
143 | * Use: All-in-one hashing function. No faster than using the |
144 | * separate calls, but more convenient. |
145 | */ |
146 | |
147 | uint32 unihash(const unihash_info *i, const void *p, size_t sz) |
148 | { |
149 | return (UNIHASH(i, p, sz)); |
150 | } |
151 | |
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152 | /*----- Test rig ----------------------------------------------------------*/ |
153 | |
154 | #ifdef TEST_RIG |
155 | |
156 | #include "testrig.h" |
157 | |
158 | static int verify(dstr *v) |
159 | { |
160 | unihash_info ui; |
161 | uint32 k; |
162 | uint32 h, hh; |
163 | size_t n; |
164 | int i, c; |
165 | const char *p; |
166 | int ok = 1; |
167 | |
168 | static const int step[] = { 0, 1, 5, 6, 7, 8, 23, -1 }; |
169 | |
170 | /* --- Set up for using this key --- */ |
171 | |
172 | k = *(uint32 *)v[0].buf; |
173 | h = *(uint32 *)v[2].buf; |
174 | unihash_setkey(&ui, k); |
175 | |
176 | /* --- Hash the data a lot --- */ |
177 | |
178 | for (i = 0; step[i] >= 0; i++) { |
179 | c = step[i]; |
180 | if (!c) |
181 | hh = unihash(&ui, v[1].buf, v[1].len); |
182 | else { |
183 | hh = UNIHASH_INIT(&ui); |
184 | p = v[1].buf; |
185 | n = v[1].len; |
186 | while (n) { |
187 | if (c > n) c = n; |
188 | hh = unihash_hash(&ui, hh, p, c); |
189 | p += c; |
190 | n -= c; |
191 | } |
192 | } |
193 | if (h != hh) { |
194 | ok = 0; |
195 | fprintf(stderr, "\nunihash failed\n"); |
196 | fprintf(stderr, " key = %08lx\n", (unsigned long)k); |
197 | fprintf(stderr, " data = %s\n", v[1].buf); |
198 | fprintf(stderr, " step = %d\n", step[i]); |
199 | fprintf(stderr, " expected = %08lx\n", (unsigned long)h); |
200 | fprintf(stderr, " computed = %08lx\n", (unsigned long)hh); |
201 | } |
202 | } |
203 | return (ok); |
204 | } |
205 | |
206 | static const test_chunk tests[] = { |
207 | { "hash", verify, { &type_uint32, &type_string, &type_uint32 } }, |
208 | { 0, 0, { 0 } } |
209 | }; |
210 | |
211 | int main(int argc, char *argv[]) |
212 | { |
213 | test_run(argc, argv, tests, "unihash.in"); |
214 | return (0); |
215 | } |
216 | |
217 | #endif |
218 | |
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219 | /*----- That's all, folks -------------------------------------------------*/ |