Line data Source code
1 : /*
2 : Unix SMB/CIFS implementation.
3 :
4 : trivial database library
5 :
6 : Copyright (C) Rusty Russell 2010
7 :
8 : ** NOTE! The following LGPL license applies to the tdb
9 : ** library. This does NOT imply that all of Samba is released
10 : ** under the LGPL
11 :
12 : This library is free software; you can redistribute it and/or
13 : modify it under the terms of the GNU Lesser General Public
14 : License as published by the Free Software Foundation; either
15 : version 3 of the License, or (at your option) any later version.
16 :
17 : This library 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 GNU
20 : Lesser General Public License for more details.
21 :
22 : You should have received a copy of the GNU Lesser General Public
23 : License along with this library; if not, see <http://www.gnu.org/licenses/>.
24 : */
25 : #include "tdb_private.h"
26 :
27 : /* This is based on the hash algorithm from gdbm */
28 586436634 : unsigned int tdb_old_hash(TDB_DATA *key)
29 : {
30 14877790 : uint32_t value; /* Used to compute the hash value. */
31 14877790 : uint32_t i; /* Used to cycle through random values. */
32 :
33 : /* Set the initial value from the key size. */
34 19385370208 : for (value = 0x238F13AF * key->dsize, i=0; i < key->dsize; i++)
35 18798933574 : value = (value + (key->dptr[i] << (i*5 % 24)));
36 :
37 586436634 : return (1103515243 * value + 12345);
38 : }
39 :
40 : #ifndef WORDS_BIGENDIAN
41 : # define HASH_LITTLE_ENDIAN 1
42 : # define HASH_BIG_ENDIAN 0
43 : #else
44 : # define HASH_LITTLE_ENDIAN 0
45 : # define HASH_BIG_ENDIAN 1
46 : #endif
47 :
48 : /*
49 : -------------------------------------------------------------------------------
50 : lookup3.c, by Bob Jenkins, May 2006, Public Domain.
51 :
52 : These are functions for producing 32-bit hashes for hash table lookup.
53 : hash_word(), hashlittle(), hashlittle2(), hashbig(), mix(), and final()
54 : are externally useful functions. Routines to test the hash are included
55 : if SELF_TEST is defined. You can use this free for any purpose. It's in
56 : the public domain. It has no warranty.
57 :
58 : You probably want to use hashlittle(). hashlittle() and hashbig()
59 : hash byte arrays. hashlittle() is faster than hashbig() on
60 : little-endian machines. Intel and AMD are little-endian machines.
61 : On second thought, you probably want hashlittle2(), which is identical to
62 : hashlittle() except it returns two 32-bit hashes for the price of one.
63 : You could implement hashbig2() if you wanted but I haven't bothered here.
64 :
65 : If you want to find a hash of, say, exactly 7 integers, do
66 : a = i1; b = i2; c = i3;
67 : mix(a,b,c);
68 : a += i4; b += i5; c += i6;
69 : mix(a,b,c);
70 : a += i7;
71 : final(a,b,c);
72 : then use c as the hash value. If you have a variable length array of
73 : 4-byte integers to hash, use hash_word(). If you have a byte array (like
74 : a character string), use hashlittle(). If you have several byte arrays, or
75 : a mix of things, see the comments above hashlittle().
76 :
77 : Why is this so big? I read 12 bytes at a time into 3 4-byte integers,
78 : then mix those integers. This is fast (you can do a lot more thorough
79 : mixing with 12*3 instructions on 3 integers than you can with 3 instructions
80 : on 1 byte), but shoehorning those bytes into integers efficiently is messy.
81 : */
82 :
83 : #define hashsize(n) ((uint32_t)1<<(n))
84 : #define hashmask(n) (hashsize(n)-1)
85 : #define rot(x,k) (((x)<<(k)) | ((x)>>(32-(k))))
86 :
87 : /*
88 : -------------------------------------------------------------------------------
89 : mix -- mix 3 32-bit values reversibly.
90 :
91 : This is reversible, so any information in (a,b,c) before mix() is
92 : still in (a,b,c) after mix().
93 :
94 : If four pairs of (a,b,c) inputs are run through mix(), or through
95 : mix() in reverse, there are at least 32 bits of the output that
96 : are sometimes the same for one pair and different for another pair.
97 : This was tested for:
98 : * pairs that differed by one bit, by two bits, in any combination
99 : of top bits of (a,b,c), or in any combination of bottom bits of
100 : (a,b,c).
101 : * "differ" is defined as +, -, ^, or ~^. For + and -, I transformed
102 : the output delta to a Gray code (a^(a>>1)) so a string of 1's (as
103 : is commonly produced by subtraction) look like a single 1-bit
104 : difference.
105 : * the base values were pseudorandom, all zero but one bit set, or
106 : all zero plus a counter that starts at zero.
107 :
108 : Some k values for my "a-=c; a^=rot(c,k); c+=b;" arrangement that
109 : satisfy this are
110 : 4 6 8 16 19 4
111 : 9 15 3 18 27 15
112 : 14 9 3 7 17 3
113 : Well, "9 15 3 18 27 15" didn't quite get 32 bits diffing
114 : for "differ" defined as + with a one-bit base and a two-bit delta. I
115 : used http://burtleburtle.net/bob/hash/avalanche.html to choose
116 : the operations, constants, and arrangements of the variables.
117 :
118 : This does not achieve avalanche. There are input bits of (a,b,c)
119 : that fail to affect some output bits of (a,b,c), especially of a. The
120 : most thoroughly mixed value is c, but it doesn't really even achieve
121 : avalanche in c.
122 :
123 : This allows some parallelism. Read-after-writes are good at doubling
124 : the number of bits affected, so the goal of mixing pulls in the opposite
125 : direction as the goal of parallelism. I did what I could. Rotates
126 : seem to cost as much as shifts on every machine I could lay my hands
127 : on, and rotates are much kinder to the top and bottom bits, so I used
128 : rotates.
129 : -------------------------------------------------------------------------------
130 : */
131 : #define mix(a,b,c) \
132 : { \
133 : a -= c; a ^= rot(c, 4); c += b; \
134 : b -= a; b ^= rot(a, 6); a += c; \
135 : c -= b; c ^= rot(b, 8); b += a; \
136 : a -= c; a ^= rot(c,16); c += b; \
137 : b -= a; b ^= rot(a,19); a += c; \
138 : c -= b; c ^= rot(b, 4); b += a; \
139 : }
140 :
141 : /*
142 : -------------------------------------------------------------------------------
143 : final -- final mixing of 3 32-bit values (a,b,c) into c
144 :
145 : Pairs of (a,b,c) values differing in only a few bits will usually
146 : produce values of c that look totally different. This was tested for
147 : * pairs that differed by one bit, by two bits, in any combination
148 : of top bits of (a,b,c), or in any combination of bottom bits of
149 : (a,b,c).
150 : * "differ" is defined as +, -, ^, or ~^. For + and -, I transformed
151 : the output delta to a Gray code (a^(a>>1)) so a string of 1's (as
152 : is commonly produced by subtraction) look like a single 1-bit
153 : difference.
154 : * the base values were pseudorandom, all zero but one bit set, or
155 : all zero plus a counter that starts at zero.
156 :
157 : These constants passed:
158 : 14 11 25 16 4 14 24
159 : 12 14 25 16 4 14 24
160 : and these came close:
161 : 4 8 15 26 3 22 24
162 : 10 8 15 26 3 22 24
163 : 11 8 15 26 3 22 24
164 : -------------------------------------------------------------------------------
165 : */
166 : #define final(a,b,c) \
167 : { \
168 : c ^= b; c -= rot(b,14); \
169 : a ^= c; a -= rot(c,11); \
170 : b ^= a; b -= rot(a,25); \
171 : c ^= b; c -= rot(b,16); \
172 : a ^= c; a -= rot(c,4); \
173 : b ^= a; b -= rot(a,14); \
174 : c ^= b; c -= rot(b,24); \
175 : }
176 :
177 :
178 : /*
179 : -------------------------------------------------------------------------------
180 : hashlittle() -- hash a variable-length key into a 32-bit value
181 : k : the key (the unaligned variable-length array of bytes)
182 : length : the length of the key, counting by bytes
183 : val2 : IN: can be any 4-byte value OUT: second 32 bit hash.
184 : Returns a 32-bit value. Every bit of the key affects every bit of
185 : the return value. Two keys differing by one or two bits will have
186 : totally different hash values. Note that the return value is better
187 : mixed than val2, so use that first.
188 :
189 : The best hash table sizes are powers of 2. There is no need to do
190 : mod a prime (mod is sooo slow!). If you need less than 32 bits,
191 : use a bitmask. For example, if you need only 10 bits, do
192 : h = (h & hashmask(10));
193 : In which case, the hash table should have hashsize(10) elements.
194 :
195 : If you are hashing n strings (uint8_t **)k, do it like this:
196 : for (i=0, h=0; i<n; ++i) h = hashlittle( k[i], len[i], h);
197 :
198 : By Bob Jenkins, 2006. bob_jenkins@burtleburtle.net. You may use this
199 : code any way you wish, private, educational, or commercial. It's free.
200 :
201 : Use for hash table lookup, or anything where one collision in 2^^32 is
202 : acceptable. Do NOT use for cryptographic purposes.
203 : -------------------------------------------------------------------------------
204 : */
205 :
206 252614315 : static uint32_t hashlittle( const void *key, size_t length )
207 : {
208 13036083 : uint32_t a,b,c; /* internal state */
209 13036083 : union { const void *ptr; size_t i; } u; /* needed for Mac Powerbook G4 */
210 :
211 : /* Set up the internal state */
212 252614315 : a = b = c = 0xdeadbeef + ((uint32_t)length);
213 :
214 252614315 : u.ptr = key;
215 252614315 : if (HASH_LITTLE_ENDIAN && ((u.i & 0x3) == 0)) {
216 238584097 : const uint32_t *k = (const uint32_t *)key; /* read 32-bit chunks */
217 : const uint8_t *k8;
218 :
219 : /*------ all but last block: aligned reads and affect 32 bits of (a,b,c) */
220 1005113072 : while (length > 12)
221 : {
222 754513979 : a += k[0];
223 754513979 : b += k[1];
224 754513979 : c += k[2];
225 754513979 : mix(a,b,c);
226 754513979 : length -= 12;
227 754513979 : k += 3;
228 : }
229 :
230 : /*----------------------------- handle the last (probably partial) block */
231 250599093 : k8 = (const uint8_t *)k;
232 250599093 : switch(length)
233 : {
234 18159611 : case 12: c+=k[2]; b+=k[1]; a+=k[0]; break;
235 11472732 : case 11: c+=((uint32_t)k8[10])<<16; FALL_THROUGH;
236 52426886 : case 10: c+=((uint32_t)k8[9])<<8; FALL_THROUGH;
237 65113054 : case 9 : c+=k8[8]; FALL_THROUGH;
238 76268451 : case 8 : b+=k[1]; a+=k[0]; break;
239 14825770 : case 7 : b+=((uint32_t)k8[6])<<16; FALL_THROUGH;
240 23494704 : case 6 : b+=((uint32_t)k8[5])<<8; FALL_THROUGH;
241 33420146 : case 5 : b+=k8[4]; FALL_THROUGH;
242 101146517 : case 4 : a+=k[0]; break;
243 8244067 : case 3 : a+=((uint32_t)k8[2])<<16; FALL_THROUGH;
244 42700539 : case 2 : a+=((uint32_t)k8[1])<<8; FALL_THROUGH;
245 55024514 : case 1 : a+=k8[0]; break;
246 0 : case 0 : return c;
247 : }
248 2015222 : } else if (HASH_LITTLE_ENDIAN && ((u.i & 0x1) == 0)) {
249 771880 : const uint16_t *k = (const uint16_t *)key; /* read 16-bit chunks */
250 : const uint8_t *k8;
251 :
252 : /*--------------- all but last block: aligned reads and different mixing */
253 807944 : while (length > 12)
254 : {
255 27659 : a += k[0] + (((uint32_t)k[1])<<16);
256 27659 : b += k[2] + (((uint32_t)k[3])<<16);
257 27659 : c += k[4] + (((uint32_t)k[5])<<16);
258 27659 : mix(a,b,c);
259 27659 : length -= 12;
260 27659 : k += 6;
261 : }
262 :
263 : /*----------------------------- handle the last (probably partial) block */
264 780285 : k8 = (const uint8_t *)k;
265 780285 : switch(length)
266 : {
267 264 : case 12: c+=k[4]+(((uint32_t)k[5])<<16);
268 264 : b+=k[2]+(((uint32_t)k[3])<<16);
269 264 : a+=k[0]+(((uint32_t)k[1])<<16);
270 264 : break;
271 743229 : case 11: c+=((uint32_t)k8[10])<<16; FALL_THROUGH;
272 743233 : case 10: c+=k[4];
273 743233 : b+=k[2]+(((uint32_t)k[3])<<16);
274 743233 : a+=k[0]+(((uint32_t)k[1])<<16);
275 743233 : break;
276 22 : case 9 : c+=k8[8]; FALL_THROUGH;
277 22 : case 8 : b+=k[2]+(((uint32_t)k[3])<<16);
278 22 : a+=k[0]+(((uint32_t)k[1])<<16);
279 22 : break;
280 10565 : case 7 : b+=((uint32_t)k8[6])<<16; FALL_THROUGH;
281 10718 : case 6 : b+=k[2];
282 10718 : a+=k[0]+(((uint32_t)k[1])<<16);
283 10718 : break;
284 13 : case 5 : b+=k8[4]; FALL_THROUGH;
285 13 : case 4 : a+=k[0]+(((uint32_t)k[1])<<16);
286 13 : break;
287 1747 : case 3 : a+=((uint32_t)k8[2])<<16; FALL_THROUGH;
288 25921 : case 2 : a+=k[0];
289 25921 : break;
290 114 : case 1 : a+=k8[0];
291 114 : break;
292 0 : case 0 : return c; /* zero length requires no mixing */
293 : }
294 :
295 : } else { /* need to read the key one byte at a time */
296 222255 : const uint8_t *k = (const uint8_t *)key;
297 :
298 : /*--------------- all but the last block: affect some 32 bits of (a,b,c) */
299 1330205 : while (length > 12)
300 : {
301 95268 : a += k[0];
302 95268 : a += ((uint32_t)k[1])<<8;
303 95268 : a += ((uint32_t)k[2])<<16;
304 95268 : a += ((uint32_t)k[3])<<24;
305 95268 : b += k[4];
306 95268 : b += ((uint32_t)k[5])<<8;
307 95268 : b += ((uint32_t)k[6])<<16;
308 95268 : b += ((uint32_t)k[7])<<24;
309 95268 : c += k[8];
310 95268 : c += ((uint32_t)k[9])<<8;
311 95268 : c += ((uint32_t)k[10])<<16;
312 95268 : c += ((uint32_t)k[11])<<24;
313 95268 : mix(a,b,c);
314 95268 : length -= 12;
315 95268 : k += 12;
316 : }
317 :
318 : /*-------------------------------- last block: affect all 32 bits of (c) */
319 1234937 : switch(length)
320 : {
321 83821 : case 12: c+=((uint32_t)k[11])<<24; FALL_THROUGH;
322 101034 : case 11: c+=((uint32_t)k[10])<<16; FALL_THROUGH;
323 101153 : case 10: c+=((uint32_t)k[9])<<8; FALL_THROUGH;
324 106732 : case 9 : c+=k[8]; FALL_THROUGH;
325 134673 : case 8 : b+=((uint32_t)k[7])<<24; FALL_THROUGH;
326 134917 : case 7 : b+=((uint32_t)k[6])<<16; FALL_THROUGH;
327 168267 : case 6 : b+=((uint32_t)k[5])<<8; FALL_THROUGH;
328 229173 : case 5 : b+=k[4]; FALL_THROUGH;
329 1229204 : case 4 : a+=((uint32_t)k[3])<<24; FALL_THROUGH;
330 1234442 : case 3 : a+=((uint32_t)k[2])<<16; FALL_THROUGH;
331 1234807 : case 2 : a+=((uint32_t)k[1])<<8; FALL_THROUGH;
332 1234937 : case 1 : a+=k[0];
333 1234937 : break;
334 0 : case 0 : return c;
335 : }
336 : }
337 :
338 252614315 : final(a,b,c);
339 252614315 : return c;
340 : }
341 :
342 252614315 : _PUBLIC_ unsigned int tdb_jenkins_hash(TDB_DATA *key)
343 : {
344 252614315 : return hashlittle(key->dptr, key->dsize);
345 : }
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