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1 | /* -*-c-*- |
2 | * |
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3 | * Simple and efficient universal hashing for hashtables |
4 | * |
5 | * (c) 2003 Straylight/Edgeware |
6 | */ |
7 | |
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8 | /*----- Licensing notice --------------------------------------------------* |
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9 | * |
10 | * This file is part of the mLib utilities library. |
11 | * |
12 | * mLib is free software; you can redistribute it and/or modify |
13 | * it under the terms of the GNU Library General Public License as |
14 | * published by the Free Software Foundation; either version 2 of the |
15 | * License, or (at your option) any later version. |
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16 | * |
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17 | * mLib is distributed in the hope that it will be useful, |
18 | * but WITHOUT ANY WARRANTY; without even the implied warranty of |
19 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
20 | * GNU Library General Public License for more details. |
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21 | * |
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22 | * You should have received a copy of the GNU Library General Public |
23 | * License along with mLib; if not, write to the Free |
24 | * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, |
25 | * MA 02111-1307, USA. |
26 | */ |
27 | |
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28 | /*----- Header files ------------------------------------------------------*/ |
29 | |
30 | #include <assert.h> |
31 | #include <stdlib.h> |
32 | |
33 | #include "unihash.h" |
34 | |
35 | /*----- Main code ---------------------------------------------------------*/ |
36 | |
37 | /* --- @unihash_setkey@ --- * |
38 | * |
39 | * Arguments: @unihash_info *i@ = where to store the precomputed tables |
40 | * @uint32 k@ = the key to set, randomly chosen |
41 | * |
42 | * Returns: --- |
43 | * |
44 | * Use: Calculates the tables required for efficient hashing. |
45 | */ |
46 | |
47 | static uint32 mul(uint32 x, uint32 y) |
48 | { |
49 | uint32 z = 0; |
50 | while (y) { |
51 | if (y & 1) z ^= x; |
52 | if (x & (1 << 31)) |
53 | x = U32(x << 1) ^ UNIHASH_POLY; |
54 | else |
55 | x = U32(x << 1); |
56 | y = U32(y >> 1); |
57 | } |
58 | return (z); |
59 | } |
60 | |
61 | void unihash_setkey(unihash_info *i, uint32 k) |
62 | { |
63 | size_t a; |
64 | size_t b; |
65 | uint32 x = 1; |
66 | |
67 | for (a = 0; a < UNIHASH_NBATCH; a++) { |
68 | x = mul(x, k); |
69 | for (b = 0; b < 256; b++) { |
70 | i->s[a][0][b] = mul(x, b << 0); |
71 | i->s[a][1][b] = mul(x, b << 8); |
72 | i->s[a][2][b] = mul(x, b << 16); |
73 | i->s[a][3][b] = mul(x, b << 24); |
74 | } |
75 | } |
76 | } |
77 | |
78 | /* --- @unihash_hash@ --- * |
79 | * |
80 | * Arguments: @const unihash_info *i@ = pointer to precomputed table |
81 | * @uint32 a@ = @i->[0][0][1]@ or value from previous call |
82 | * @const void *p@ = pointer to data to hash |
83 | * @size_t sz@ = size of the data |
84 | * |
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85 | * Returns: Hash of data so far. |
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86 | * |
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87 | * Use: Hashes data. Call this as many times as needed. |
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88 | */ |
89 | |
90 | uint32 unihash_hash(const unihash_info *i, uint32 a, |
91 | const void *p, size_t sz) |
92 | { |
93 | const octet *pp = p; |
94 | |
95 | assert(UNIHASH_NBATCH == 4); |
96 | |
97 | #define FULLMULT(u, x) \ |
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98 | (i->s[u][0][U8((x) >> 0)] ^ i->s[u][1][U8((x) >> 8)] ^ \ |
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99 | i->s[u][2][U8((x) >> 16)] ^ i->s[u][3][U8((x) >> 24)]); |
100 | |
101 | #define BYTEMULT(u, x) i->s[u][0][x] |
102 | |
103 | /* --- Do the main bulk in batches of %$n$% bytes --- * |
104 | * |
105 | * We have %$a$% and %$m_{n-1}, \ldots, m_1, m_0$%; we want |
106 | * |
107 | * %$a' = (a + m_{n-1}) k^n + m_{n-2} k^{n-1} + \cdots + m_1 k^2 + m_0 k$% |
108 | */ |
109 | |
110 | while (sz >= UNIHASH_NBATCH) { |
111 | a ^= *pp++; |
112 | a = FULLMULT(3, a); |
113 | a ^= BYTEMULT(2, *pp++); |
114 | a ^= BYTEMULT(1, *pp++); |
115 | a ^= BYTEMULT(0, *pp++); |
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116 | sz -= UNIHASH_NBATCH; |
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117 | } |
118 | |
119 | /* --- The tail end is a smaller batch --- */ |
120 | |
121 | switch (sz) { |
122 | case 3: a ^= *pp++; a = FULLMULT(2, a); goto batch_2; |
123 | case 2: a ^= *pp++; a = FULLMULT(1, a); goto batch_1; |
124 | case 1: a ^= *pp++; a = FULLMULT(0, a); goto batch_0; |
125 | batch_2: a ^= BYTEMULT(1, *pp++); |
126 | batch_1: a ^= BYTEMULT(0, *pp++); |
127 | batch_0: break; |
128 | } |
129 | |
130 | return (a); |
131 | } |
132 | |
133 | /* --- @unihash@ --- * |
134 | * |
135 | * Arguments: @const unihash_info *i@ = precomputed tables |
136 | * @const void *p@ = pointer to data to hash |
137 | * @size_t sz@ = size of the data |
138 | * |
139 | * Returns: The hash value computed. |
140 | * |
141 | * Use: All-in-one hashing function. No faster than using the |
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142 | * separate calls, but more convenient. |
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143 | */ |
144 | |
145 | uint32 unihash(const unihash_info *i, const void *p, size_t sz) |
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146 | { return (UNIHASH(i, p, sz)); } |
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147 | |
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148 | /*----- That's all, folks -------------------------------------------------*/ |