Multiple fixes when cleaning app and UST sessions
[lttng-tools.git] / hashtable / hash.c
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1/*
2 * Copyright (C) - Bob Jenkins, May 2006, Public Domain.
3 * Copyright (C) 2011 - David Goulet <david.goulet@polymtl.ca>
4 *
5 * These are functions for producing 32-bit hashes for hash table lookup.
6 * hashword(), hashlittle(), hashlittle2(), hashbig(), mix(), and final() are
7 * externally useful functions. Routines to test the hash are included if
8 * SELF_TEST is defined. You can use this free for any purpose. It's in the
9 * public domain. It has no warranty.
10 *
11 * You probably want to use hashlittle(). hashlittle() and hashbig() hash byte
12 * arrays. hashlittle() is is faster than hashbig() on little-endian machines.
13 * Intel and AMD are little-endian machines. On second thought, you probably
14 * want hashlittle2(), which is identical to hashlittle() except it returns two
15 * 32-bit hashes for the price of one. You could implement hashbig2() if you
16 * wanted but I haven't bothered here.
17 *
18 * If you want to find a hash of, say, exactly 7 integers, do
19 * a = i1; b = i2; c = i3;
20 * mix(a,b,c);
21 * a += i4; b += i5; c += i6;
22 * mix(a,b,c);
23 * a += i7;
24 * final(a,b,c);
25 * then use c as the hash value. If you have a variable length array of
26 * 4-byte integers to hash, use hashword(). If you have a byte array (like
27 * a character string), use hashlittle(). If you have several byte arrays, or
28 * a mix of things, see the comments above hashlittle().
29 *
30 * Why is this so big? I read 12 bytes at a time into 3 4-byte integers, then
31 * mix those integers. This is fast (you can do a lot more thorough mixing
32 * with 12*3 instructions on 3 integers than you can with 3 instructions on 1
33 * byte), but shoehorning those bytes into integers efficiently is messy.
34 */
35
36#include <stdio.h> /* defines printf for tests */
37#include <time.h> /* defines time_t for timings in the test */
38#include <stdint.h> /* defines uint32_t etc */
39#include <sys/param.h> /* attempt to define endianness */
40#include <endian.h> /* attempt to define endianness */
41#include <string.h>
42#include <assert.h>
43
44/*
45 * My best guess at if you are big-endian or little-endian. This may
46 * need adjustment.
47 */
48#if (defined(__BYTE_ORDER) && defined(__LITTLE_ENDIAN) && \
49 __BYTE_ORDER == __LITTLE_ENDIAN) || \
50 (defined(i386) || defined(__i386__) || defined(__i486__) || \
51 defined(__i586__) || defined(__i686__) || defined(vax) || defined(MIPSEL))
52# define HASH_LITTLE_ENDIAN 1
53# define HASH_BIG_ENDIAN 0
54#elif (defined(__BYTE_ORDER) && defined(__BIG_ENDIAN) && \
55 __BYTE_ORDER == __BIG_ENDIAN) || \
56 (defined(sparc) || defined(POWERPC) || defined(mc68000) || defined(sel))
57# define HASH_LITTLE_ENDIAN 0
58# define HASH_BIG_ENDIAN 1
59#else
60# define HASH_LITTLE_ENDIAN 0
61# define HASH_BIG_ENDIAN 0
62#endif
63
64#define hashsize(n) ((uint32_t)1<<(n))
65#define hashmask(n) (hashsize(n)-1)
66#define rot(x,k) (((x)<<(k)) | ((x)>>(32-(k))))
67
68/*
69 * mix -- mix 3 32-bit values reversibly.
70 *
71 * This is reversible, so any information in (a,b,c) before mix() is
72 * still in (a,b,c) after mix().
73 *
74 * If four pairs of (a,b,c) inputs are run through mix(), or through
75 * mix() in reverse, there are at least 32 bits of the output that
76 * are sometimes the same for one pair and different for another pair.
77 * This was tested for:
78 * * pairs that differed by one bit, by two bits, in any combination
79 * of top bits of (a,b,c), or in any combination of bottom bits of
80 * (a,b,c).
81 * * "differ" is defined as +, -, ^, or ~^. For + and -, I transformed
82 * the output delta to a Gray code (a^(a>>1)) so a string of 1's (as
83 * is commonly produced by subtraction) look like a single 1-bit
84 * difference.
85 * * the base values were pseudorandom, all zero but one bit set, or
86 * all zero plus a counter that starts at zero.
87 *
88 * Some k values for my "a-=c; a^=rot(c,k); c+=b;" arrangement that
89 * satisfy this are
90 * 4 6 8 16 19 4
91 * 9 15 3 18 27 15
92 * 14 9 3 7 17 3
93 * Well, "9 15 3 18 27 15" didn't quite get 32 bits diffing
94 * for "differ" defined as + with a one-bit base and a two-bit delta. I
95 * used http://burtleburtle.net/bob/hash/avalanche.html to choose
96 * the operations, constants, and arrangements of the variables.
97 *
98 * This does not achieve avalanche. There are input bits of (a,b,c)
99 * that fail to affect some output bits of (a,b,c), especially of a. The
100 * most thoroughly mixed value is c, but it doesn't really even achieve
101 * avalanche in c.
102 *
103 * This allows some parallelism. Read-after-writes are good at doubling
104 * the number of bits affected, so the goal of mixing pulls in the opposite
105 * direction as the goal of parallelism. I did what I could. Rotates
106 * seem to cost as much as shifts on every machine I could lay my hands
107 * on, and rotates are much kinder to the top and bottom bits, so I used
108 * rotates.
109 */
110#define mix(a,b,c) \
111{ \
112 a -= c; a ^= rot(c, 4); c += b; \
113 b -= a; b ^= rot(a, 6); a += c; \
114 c -= b; c ^= rot(b, 8); b += a; \
115 a -= c; a ^= rot(c,16); c += b; \
116 b -= a; b ^= rot(a,19); a += c; \
117 c -= b; c ^= rot(b, 4); b += a; \
118}
119
120/*
121 * final -- final mixing of 3 32-bit values (a,b,c) into c
122 *
123 * Pairs of (a,b,c) values differing in only a few bits will usually
124 * produce values of c that look totally different. This was tested for
125 * * pairs that differed by one bit, by two bits, in any combination
126 * of top bits of (a,b,c), or in any combination of bottom bits of
127 * (a,b,c).
128 * * "differ" is defined as +, -, ^, or ~^. For + and -, I transformed
129 * the output delta to a Gray code (a^(a>>1)) so a string of 1's (as
130 * is commonly produced by subtraction) look like a single 1-bit
131 * difference.
132 * * the base values were pseudorandom, all zero but one bit set, or
133 * all zero plus a counter that starts at zero.
134 *
135 * These constants passed:
136 * 14 11 25 16 4 14 24
137 * 12 14 25 16 4 14 24
138 * and these came close:
139 * 4 8 15 26 3 22 24
140 * 10 8 15 26 3 22 24
141 * 11 8 15 26 3 22 24
142 */
143#define final(a,b,c) \
144{ \
145 c ^= b; c -= rot(b,14); \
146 a ^= c; a -= rot(c,11); \
147 b ^= a; b -= rot(a,25); \
148 c ^= b; c -= rot(b,16); \
149 a ^= c; a -= rot(c,4); \
150 b ^= a; b -= rot(a,14); \
151 c ^= b; c -= rot(b,24); \
152}
153
154/*
155 * hashword2() -- same as hashword(), but take two seeds and return two 32-bit
156 * values. pc and pb must both be nonnull, and *pc and *pb must both be
157 * initialized with seeds. If you pass in (*pb)==0, the output (*pc) will be
158 * the same as the return value from hashword().
159 */
160static void hashword2(const uint32_t *k, size_t length,
161 uint32_t *pc, uint32_t *pb)
162{
163 uint32_t a, b, c;
164
165 /* Set up the internal state */
166 a = b = c = 0xdeadbeef + ((uint32_t) (length << 2)) + *pc;
167 c += *pb;
168
169 while (length > 3) {
170 a += k[0];
171 b += k[1];
172 c += k[2];
173 mix(a, b, c);
174 length -= 3;
175 k += 3;
176 }
177
178 switch (length) {
179 case 3 :
180 c += k[2];
181 case 2 :
182 b += k[1];
183 case 1 :
184 a += k[0];
185 final(a, b, c);
186 case 0: /* case 0: nothing left to add */
187 break;
188 }
189
190 *pc = c;
191 *pb = b;
192}
193
194/*
195 * hashlittle() -- hash a variable-length key into a 32-bit value
196 * k : the key (the unaligned variable-length array of bytes)
197 * length : the length of the key, counting by bytes
198 * initval : can be any 4-byte value
199 * Returns a 32-bit value. Every bit of the key affects every bit of
200 * the return value. Two keys differing by one or two bits will have
201 * totally different hash values.
202 *
203 * The best hash table sizes are powers of 2. There is no need to do
204 * mod a prime (mod is sooo slow!). If you need less than 32 bits,
205 * use a bitmask. For example, if you need only 10 bits, do
206 * h = (h & hashmask(10));
207 * In which case, the hash table should have hashsize(10) elements.
208 *
209 * If you are hashing n strings (uint8_t **)k, do it like this:
210 * for (i=0, h=0; i<n; ++i) h = hashlittle( k[i], len[i], h);
211 *
212 * By Bob Jenkins, 2006. bob_jenkins@burtleburtle.net. You may use this
213 * code any way you wish, private, educational, or commercial. It's free.
214 *
215 * Use for hash table lookup, or anything where one collision in 2^^32 is
216 * acceptable. Do NOT use for cryptographic purposes.
217 */
218
219static uint32_t hashlittle(const void *key, size_t length, uint32_t initval)
220{
221 uint32_t a,b,c;
222 union {
223 const void *ptr;
224 size_t i;
225 } u; /* needed for Mac Powerbook G4 */
226
227 /* Set up the internal state */
228 a = b = c = 0xdeadbeef + ((uint32_t)length) + initval;
229
230 u.ptr = key;
231 if (HASH_LITTLE_ENDIAN && ((u.i & 0x3) == 0)) {
232 const uint32_t *k = (const uint32_t *)key; /* read 32-bit chunks */
233
234 /*------ all but last block: aligned reads and affect 32 bits of (a,b,c) */
235 while (length > 12) {
236 a += k[0];
237 b += k[1];
238 c += k[2];
239 mix(a,b,c);
240 length -= 12;
241 k += 3;
242 }
243
244 /*
245 * "k[2]&0xffffff" actually reads beyond the end of the string, but
246 * then masks off the part it's not allowed to read. Because the
247 * string is aligned, the masked-off tail is in the same word as the
248 * rest of the string. Every machine with memory protection I've seen
249 * does it on word boundaries, so is OK with this. But VALGRIND will
250 * still catch it and complain. The masking trick does make the hash
251 * noticably faster for short strings (like English words).
252 */
253#ifndef VALGRIND
254
255 switch (length) {
256 case 12: c+=k[2]; b+=k[1]; a+=k[0]; break;
257 case 11: c+=k[2]&0xffffff; b+=k[1]; a+=k[0]; break;
258 case 10: c+=k[2]&0xffff; b+=k[1]; a+=k[0]; break;
259 case 9 : c+=k[2]&0xff; b+=k[1]; a+=k[0]; break;
260 case 8 : b+=k[1]; a+=k[0]; break;
261 case 7 : b+=k[1]&0xffffff; a+=k[0]; break;
262 case 6 : b+=k[1]&0xffff; a+=k[0]; break;
263 case 5 : b+=k[1]&0xff; a+=k[0]; break;
264 case 4 : a+=k[0]; break;
265 case 3 : a+=k[0]&0xffffff; break;
266 case 2 : a+=k[0]&0xffff; break;
267 case 1 : a+=k[0]&0xff; break;
268 case 0 : return c; /* zero length strings require no mixing */
269 }
270#else /* make valgrind happy */
271 const uint8_t *k8;
272
273 k8 = (const uint8_t *)k;
274 switch (length) {
275 case 12: c+=k[2]; b+=k[1]; a+=k[0]; break;
276 case 11: c+=((uint32_t)k8[10])<<16; /* fall through */
277 case 10: c+=((uint32_t)k8[9])<<8; /* fall through */
278 case 9 : c+=k8[8]; /* fall through */
279 case 8 : b+=k[1]; a+=k[0]; break;
280 case 7 : b+=((uint32_t)k8[6])<<16; /* fall through */
281 case 6 : b+=((uint32_t)k8[5])<<8; /* fall through */
282 case 5 : b+=k8[4]; /* fall through */
283 case 4 : a+=k[0]; break;
284 case 3 : a+=((uint32_t)k8[2])<<16; /* fall through */
285 case 2 : a+=((uint32_t)k8[1])<<8; /* fall through */
286 case 1 : a+=k8[0]; break;
287 case 0 : return c;
288 }
289#endif /* !valgrind */
290 } else if (HASH_LITTLE_ENDIAN && ((u.i & 0x1) == 0)) {
291 const uint16_t *k = (const uint16_t *)key; /* read 16-bit chunks */
292 const uint8_t *k8;
293
294 /*--------------- all but last block: aligned reads and different mixing */
295 while (length > 12) {
296 a += k[0] + (((uint32_t)k[1])<<16);
297 b += k[2] + (((uint32_t)k[3])<<16);
298 c += k[4] + (((uint32_t)k[5])<<16);
299 mix(a,b,c);
300 length -= 12;
301 k += 6;
302 }
303
304 k8 = (const uint8_t *)k;
305 switch (length) {
306 case 12:
307 c+=k[4]+(((uint32_t)k[5])<<16);
308 b+=k[2]+(((uint32_t)k[3])<<16);
309 a+=k[0]+(((uint32_t)k[1])<<16);
310 break;
311 case 11:
312 c+=((uint32_t)k8[10])<<16; /* fall through */
313 case 10:
314 c+=k[4];
315 b+=k[2]+(((uint32_t)k[3])<<16);
316 a+=k[0]+(((uint32_t)k[1])<<16);
317 break;
318 case 9:
319 c+=k8[8]; /* fall through */
320 case 8:
321 b+=k[2]+(((uint32_t)k[3])<<16);
322 a+=k[0]+(((uint32_t)k[1])<<16);
323 break;
324 case 7:
325 b+=((uint32_t)k8[6])<<16; /* fall through */
326 case 6:
327 b+=k[2];
328 a+=k[0]+(((uint32_t)k[1])<<16);
329 break;
330 case 5:
331 b+=k8[4]; /* fall through */
332 case 4:
333 a+=k[0]+(((uint32_t)k[1])<<16);
334 break;
335 case 3:
336 a+=((uint32_t)k8[2])<<16; /* fall through */
337 case 2:
338 a+=k[0];
339 break;
340 case 1:
341 a+=k8[0];
342 break;
343 case 0:
344 return c; /* zero length requires no mixing */
345 }
346
347 } else { /* need to read the key one byte at a time */
348 const uint8_t *k = (const uint8_t *)key;
349
350 while (length > 12) {
351 a += k[0];
352 a += ((uint32_t)k[1])<<8;
353 a += ((uint32_t)k[2])<<16;
354 a += ((uint32_t)k[3])<<24;
355 b += k[4];
356 b += ((uint32_t)k[5])<<8;
357 b += ((uint32_t)k[6])<<16;
358 b += ((uint32_t)k[7])<<24;
359 c += k[8];
360 c += ((uint32_t)k[9])<<8;
361 c += ((uint32_t)k[10])<<16;
362 c += ((uint32_t)k[11])<<24;
363 mix(a,b,c);
364 length -= 12;
365 k += 12;
366 }
367
368 switch(length) { /* all the case statements fall through */
369 case 12: c+=((uint32_t)k[11])<<24;
370 case 11: c+=((uint32_t)k[10])<<16;
371 case 10: c+=((uint32_t)k[9])<<8;
372 case 9: c+=k[8];
373 case 8: b+=((uint32_t)k[7])<<24;
374 case 7: b+=((uint32_t)k[6])<<16;
375 case 6: b+=((uint32_t)k[5])<<8;
376 case 5: b+=k[4];
377 case 4: a+=((uint32_t)k[3])<<24;
378 case 3: a+=((uint32_t)k[2])<<16;
379 case 2: a+=((uint32_t)k[1])<<8;
380 case 1:
381 a+=k[0];
382 break;
383 case 0:
384 return c;
385 }
386 }
387
388 final(a,b,c);
389 return c;
390}
391
392/*
393 * Hash function for number value.
394 */
395unsigned long hash_key(void *_key, size_t length, unsigned long seed)
396{
397 union {
398 uint64_t v64;
399 uint32_t v32[2];
400 } v;
401 union {
402 uint64_t v64;
403 uint32_t v32[2];
404 } key;
405
406 assert(length == sizeof(unsigned long));
407 v.v64 = (uint64_t) seed;
408 key.v64 = (uint64_t) _key;
409 hashword2(key.v32, 2, &v.v32[0], &v.v32[1]);
410 return v.v64;
411}
412
413/*
414 * Hash function for string.
415 */
416unsigned long hash_key_str(void *key, size_t length, unsigned long seed)
417{
418 return hashlittle(key, length, seed);
419}
420
421/*
422 * Hash function compare for number value.
423 */
424unsigned long hash_compare_key(void *key1, size_t key1_len,
425 void *key2, size_t key2_len)
426{
427 if (key1_len != key2_len) {
428 return -1;
429 }
430
431 if (key1 == key2) {
432 return 0;
433 }
434
435 return 1;
436}
437
438/*
439 * Hash compare function for string.
440 */
441unsigned long hash_compare_key_str(void *key1, size_t key1_len,
442 void *key2, size_t key2_len)
443{
444 if (key1_len != key2_len) {
445 return -1;
446 }
447
448 if (strncmp(key1, key2, key1_len) == 0) {
449 return 0;
450 }
451
452 return 1;
453}
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