3 * $Id: unihash.c,v 1.2 2003/12/14 14:45:30 mdw Exp $
5 * Simple and efficient universal hashing for hashtables
7 * (c) 2003 Straylight/Edgeware
10 /*----- Licensing notice --------------------------------------------------*
12 * This file is part of the mLib utilities library.
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.
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.
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,
30 /*----- Revision history --------------------------------------------------*
33 * Revision 1.2 2003/12/14 14:45:30 mdw
34 * Test universal hashing and fix bugs.
36 * Revision 1.1 2003/10/12 14:43:24 mdw
41 /*----- Header files ------------------------------------------------------*/
48 /*----- Main code ---------------------------------------------------------*/
50 /* --- @unihash_setkey@ --- *
52 * Arguments: @unihash_info *i@ = where to store the precomputed tables
53 * @uint32 k@ = the key to set, randomly chosen
57 * Use: Calculates the tables required for efficient hashing.
60 static uint32
mul(uint32 x
, uint32 y
)
66 x
= U32(x
<< 1) ^ UNIHASH_POLY
;
74 void unihash_setkey(unihash_info
*i
, uint32 k
)
80 for (a
= 0; a
< UNIHASH_NBATCH
; a
++) {
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);
91 /* --- @unihash_hash@ --- *
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
98 * Returns: Hash of data so far.
100 * Use: Hashes data. Call this as many times as needed.
103 uint32
unihash_hash(const unihash_info
*i
, uint32 a
,
104 const void *p
, size_t sz
)
108 assert(UNIHASH_NBATCH
== 4);
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)]);
114 #define BYTEMULT(u, x) i->s[u][0][x]
116 /* --- Do the main bulk in batches of %$n$% bytes --- *
118 * We have %$a$% and %$m_{n-1}, \ldots, m_1, m_0$%; we want
120 * %$a' = (a + m_{n-1}) k^n + m_{n-2} k^{n-1} + \cdots + m_1 k^2 + m_0 k$%
123 while (sz
>= UNIHASH_NBATCH
) {
126 a
^= BYTEMULT(2, *pp
++);
127 a
^= BYTEMULT(1, *pp
++);
128 a
^= BYTEMULT(0, *pp
++);
129 sz
-= UNIHASH_NBATCH
;
132 /* --- The tail end is a smaller batch --- */
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
++);
146 /* --- @unihash@ --- *
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
152 * Returns: The hash value computed.
154 * Use: All-in-one hashing function. No faster than using the
155 * separate calls, but more convenient.
158 uint32
unihash(const unihash_info
*i
, const void *p
, size_t sz
)
160 return (UNIHASH(i
, p
, sz
));
163 /*----- Test rig ----------------------------------------------------------*/
169 static int verify(dstr
*v
)
179 static const int step
[] = { 0, 1, 5, 6, 7, 8, 23, -1 };
181 /* --- Set up for using this key --- */
183 k
= *(uint32
*)v
[0].buf
;
184 h
= *(uint32
*)v
[2].buf
;
185 unihash_setkey(&ui
, k
);
187 /* --- Hash the data a lot --- */
189 for (i
= 0; step
[i
] >= 0; i
++) {
192 hh
= unihash(&ui
, v
[1].buf
, v
[1].len
);
194 hh
= UNIHASH_INIT(&ui
);
199 hh
= unihash_hash(&ui
, hh
, p
, c
);
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
);
217 static const test_chunk tests
[] = {
218 { "hash", verify
, { &type_uint32
, &type_string
, &type_uint32
} },
222 int main(int argc
, char *argv
[])
224 test_run(argc
, argv
, tests
, "unihash.in");
230 /*----- That's all, folks -------------------------------------------------*/