liblttng-ht/utils.c

   1 /*
   2  * Copyright (C) - Bob Jenkins, May 2006, Public Domain.
   3  * Copyright (C) 2011 - David Goulet <david.goulet@polymtl.ca>
   4  * Copyright (C) 2011 - Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
   5  *
   6  * These are functions for producing 32-bit hashes for hash table lookup.
   7  * hashword(), hashlittle(), hashlittle2(), hashbig(), mix(), and final() are
   8  * externally useful functions.  Routines to test the hash are included if
   9  * SELF_TEST is defined.  You can use this free for any purpose.  It's in the
  10  * public domain.  It has no warranty.
  11  *
  12  * You probably want to use hashlittle().  hashlittle() and hashbig() hash byte
  13  * arrays.  hashlittle() is is faster than hashbig() on little-endian machines.
  14  * Intel and AMD are little-endian machines.  On second thought, you probably
  15  * want hashlittle2(), which is identical to hashlittle() except it returns two
  16  * 32-bit hashes for the price of one.  You could implement hashbig2() if you
  17  * wanted but I haven't bothered here.
  18  *
  19  * If you want to find a hash of, say, exactly 7 integers, do
  20  *   a = i1;  b = i2;  c = i3;
  21  *   mix(a,b,c);
  22  *   a += i4; b += i5; c += i6;
  23  *   mix(a,b,c);
  24  *   a += i7;
  25  *   final(a,b,c);
  26  * then use c as the hash value.  If you have a variable length array of
  27  * 4-byte integers to hash, use hashword().  If you have a byte array (like
  28  * a character string), use hashlittle().  If you have several byte arrays, or
  29  * a mix of things, see the comments above hashlittle().
  30  *
  31  * Why is this so big?  I read 12 bytes at a time into 3 4-byte integers, then
  32  * mix those integers.  This is fast (you can do a lot more thorough mixing
  33  * with 12*3 instructions on 3 integers than you can with 3 instructions on 1
  34  * byte), but shoehorning those bytes into integers efficiently is messy.
  35  */
  36
  37 #include <assert.h>
  38 #include <endian.h>    /* attempt to define endianness */
  39 #include <stdint.h>     /* defines uint32_t etc */
  40 #include <stdio.h>      /* defines printf for tests */
  41 #include <string.h>
  42 #include <sys/param.h>  /* attempt to define endianness */
  43 #include <time.h>       /* defines time_t for timings in the test */
  44 #include <urcu/compiler.h>
  45
  46 #include "utils.h"
  47
  48 /*
  49  * My best guess at if you are big-endian or little-endian.  This may
  50  * need adjustment.
  51  */
  52 #if (defined(__BYTE_ORDER) && defined(__LITTLE_ENDIAN) && \
  53      __BYTE_ORDER == __LITTLE_ENDIAN) || \
  54     (defined(i386) || defined(__i386__) || defined(__i486__) || \
  55      defined(__i586__) || defined(__i686__) || defined(vax) || defined(MIPSEL))
  56 # define HASH_LITTLE_ENDIAN 1
  57 # define HASH_BIG_ENDIAN 0
  58 #elif (defined(__BYTE_ORDER) && defined(__BIG_ENDIAN) && \
  59        __BYTE_ORDER == __BIG_ENDIAN) || \
  60       (defined(sparc) || defined(POWERPC) || defined(mc68000) || defined(sel))
  61 # define HASH_LITTLE_ENDIAN 0
  62 # define HASH_BIG_ENDIAN 1
  63 #else
  64 # define HASH_LITTLE_ENDIAN 0
  65 # define HASH_BIG_ENDIAN 0
  66 #endif
  67
  68 #define hashsize(n) ((uint32_t)1<<(n))
  69 #define hashmask(n) (hashsize(n)-1)
  70 #define rot(x,k) (((x)<<(k)) | ((x)>>(32-(k))))
  71
  72 /*
  73  * mix -- mix 3 32-bit values reversibly.
  74  *
  75  * This is reversible, so any information in (a,b,c) before mix() is
  76  * still in (a,b,c) after mix().
  77  *
  78  * If four pairs of (a,b,c) inputs are run through mix(), or through
  79  * mix() in reverse, there are at least 32 bits of the output that
  80  * are sometimes the same for one pair and different for another pair.
  81  * This was tested for:
  82  * * pairs that differed by one bit, by two bits, in any combination
  83  *   of top bits of (a,b,c), or in any combination of bottom bits of
  84  *   (a,b,c).
  85  * * "differ" is defined as +, -, ^, or ~^.  For + and -, I transformed
  86  *   the output delta to a Gray code (a^(a>>1)) so a string of 1's (as
  87  *   is commonly produced by subtraction) look like a single 1-bit
  88  *   difference.
  89  * * the base values were pseudorandom, all zero but one bit set, or
  90  *   all zero plus a counter that starts at zero.
  91  *
  92  * Some k values for my "a-=c; a^=rot(c,k); c+=b;" arrangement that
  93  * satisfy this are
  94  *     4  6  8 16 19  4
  95  *     9 15  3 18 27 15
  96  *    14  9  3  7 17  3
  97  * Well, "9 15 3 18 27 15" didn't quite get 32 bits diffing
  98  * for "differ" defined as + with a one-bit base and a two-bit delta.  I
  99  * used http://burtleburtle.net/bob/hash/avalanche.html to choose
 100  * the operations, constants, and arrangements of the variables.
 101  *
 102  * This does not achieve avalanche.  There are input bits of (a,b,c)
 103  * that fail to affect some output bits of (a,b,c), especially of a.  The
 104  * most thoroughly mixed value is c, but it doesn't really even achieve
 105  * avalanche in c.
 106  *
 107  * This allows some parallelism.  Read-after-writes are good at doubling
 108  * the number of bits affected, so the goal of mixing pulls in the opposite
 109  * direction as the goal of parallelism.  I did what I could.  Rotates
 110  * seem to cost as much as shifts on every machine I could lay my hands
 111  * on, and rotates are much kinder to the top and bottom bits, so I used
 112  * rotates.
 113  */
 114 #define mix(a,b,c) \
 115 { \
 116   a -= c;  a ^= rot(c, 4);  c += b; \
 117   b -= a;  b ^= rot(a, 6);  a += c; \
 118   c -= b;  c ^= rot(b, 8);  b += a; \
 119   a -= c;  a ^= rot(c,16);  c += b; \
 120   b -= a;  b ^= rot(a,19);  a += c; \
 121   c -= b;  c ^= rot(b, 4);  b += a; \
 122 }
 123
 124 /*
 125  * final -- final mixing of 3 32-bit values (a,b,c) into c
 126  *
 127  * Pairs of (a,b,c) values differing in only a few bits will usually
 128  * produce values of c that look totally different.  This was tested for
 129  * * pairs that differed by one bit, by two bits, in any combination
 130  *   of top bits of (a,b,c), or in any combination of bottom bits of
 131  *   (a,b,c).
 132  * * "differ" is defined as +, -, ^, or ~^.  For + and -, I transformed
 133  *   the output delta to a Gray code (a^(a>>1)) so a string of 1's (as
 134  *   is commonly produced by subtraction) look like a single 1-bit
 135  *   difference.
 136  * * the base values were pseudorandom, all zero but one bit set, or
 137  *   all zero plus a counter that starts at zero.
 138  *
 139  * These constants passed:
 140  *  14 11 25 16 4 14 24
 141  *  12 14 25 16 4 14 24
 142  * and these came close:
 143  *   4  8 15 26 3 22 24
 144  *  10  8 15 26 3 22 24
 145  *  11  8 15 26 3 22 24
 146  */
 147 #define final(a,b,c) \
 148 { \
 149   c ^= b; c -= rot(b,14); \
 150   a ^= c; a -= rot(c,11); \
 151   b ^= a; b -= rot(a,25); \
 152   c ^= b; c -= rot(b,16); \
 153   a ^= c; a -= rot(c,4);  \
 154   b ^= a; b -= rot(a,14); \
 155   c ^= b; c -= rot(b,24); \
 156 }
 157
 158 /*
 159  * k - the key, an array of uint32_t values
 160  * length - the length of the key, in uint32_ts
 161  * initval - the previous hash, or an arbitrary value
 162  */
 163 static uint32_t __attribute__((unused)) hashword(const uint32_t *k,
 164                 size_t length, uint32_t initval)
 165 {
 166         uint32_t a, b, c;
 167
 168         /* Set up the internal state */
 169         a = b = c = 0xdeadbeef + (((uint32_t) length) << 2) + initval;
 170
 171         /*----------------------------------------- handle most of the key */
 172         while (length > 3) {
 173                 a += k[0];
 174                 b += k[1];
 175                 c += k[2];
 176                 mix(a, b, c);
 177                 length -= 3;
 178                 k += 3;
 179         }
 180
 181         /*----------------------------------- handle the last 3 uint32_t's */
 182         switch (length) {       /* all the case statements fall through */
 183         case 3: c += k[2];
 184         case 2: b += k[1];
 185         case 1: a += k[0];
 186                 final(a, b, c);
 187         case 0:                 /* case 0: nothing left to add */
 188                 break;
 189         }
 190         /*---------------------------------------------- report the result */
 191         return c;
 192 }
 193
 194
 195 /*
 196  * hashword2() -- same as hashword(), but take two seeds and return two 32-bit
 197  * values.  pc and pb must both be nonnull, and *pc and *pb must both be
 198  * initialized with seeds.  If you pass in (*pb)==0, the output (*pc) will be
 199  * the same as the return value from hashword().
 200  */
 201 static void __attribute__((unused)) hashword2(const uint32_t *k, size_t length,
 202                 uint32_t *pc, uint32_t *pb)
 203 {
 204         uint32_t a, b, c;
 205
 206         /* Set up the internal state */
 207         a = b = c = 0xdeadbeef + ((uint32_t) (length << 2)) + *pc;
 208         c += *pb;
 209
 210         while (length > 3) {
 211                 a += k[0];
 212                 b += k[1];
 213                 c += k[2];
 214                 mix(a, b, c);
 215                 length -= 3;
 216                 k += 3;
 217         }
 218
 219         switch (length) {
 220         case 3 :
 221                 c += k[2];
 222         case 2 :
 223                 b += k[1];
 224         case 1 :
 225                 a += k[0];
 226                 final(a, b, c);
 227         case 0:     /* case 0: nothing left to add */
 228                 break;
 229         }
 230
 231         *pc = c;
 232         *pb = b;
 233 }
 234
 235 /*
 236  * hashlittle() -- hash a variable-length key into a 32-bit value
 237  *   k       : the key (the unaligned variable-length array of bytes)
 238  *   length  : the length of the key, counting by bytes
 239  *   initval : can be any 4-byte value
 240  * Returns a 32-bit value.  Every bit of the key affects every bit of
 241  * the return value.  Two keys differing by one or two bits will have
 242  * totally different hash values.
 243  *
 244  * The best hash table sizes are powers of 2.  There is no need to do
 245  * mod a prime (mod is sooo slow!).  If you need less than 32 bits,
 246  * use a bitmask.  For example, if you need only 10 bits, do
 247  *   h = (h & hashmask(10));
 248  * In which case, the hash table should have hashsize(10) elements.
 249  *
 250  * If you are hashing n strings (uint8_t **)k, do it like this:
 251  *   for (i=0, h=0; i<n; ++i) h = hashlittle( k[i], len[i], h);
 252  *
 253  * By Bob Jenkins, 2006.  bob_jenkins@burtleburtle.net.  You may use this
 254  * code any way you wish, private, educational, or commercial.  It's free.
 255  *
 256  * Use for hash table lookup, or anything where one collision in 2^^32 is
 257  * acceptable.  Do NOT use for cryptographic purposes.
 258  */
 259 static uint32_t __attribute__((unused)) hashlittle(const void *key,
 260                 size_t length, uint32_t initval)
 261 {
 262         uint32_t a,b,c;
 263         union {
 264                 const void *ptr;
 265                 size_t i;
 266         } u;     /* needed for Mac Powerbook G4 */
 267
 268         /* Set up the internal state */
 269         a = b = c = 0xdeadbeef + ((uint32_t)length) + initval;
 270
 271         u.ptr = key;
 272         if (HASH_LITTLE_ENDIAN && ((u.i & 0x3) == 0)) {
 273                 const uint32_t *k = (const uint32_t *)key;         /* read 32-bit chunks */
 274
 275                 /*------ all but last block: aligned reads and affect 32 bits of (a,b,c) */
 276                 while (length > 12) {
 277                         a += k[0];
 278                         b += k[1];
 279                         c += k[2];
 280                         mix(a,b,c);
 281                         length -= 12;
 282                         k += 3;
 283                 }
 284
 285                 /*
 286                  * "k[2]&0xffffff" actually reads beyond the end of the string, but
 287                  * then masks off the part it's not allowed to read.  Because the
 288                  * string is aligned, the masked-off tail is in the same word as the
 289                  * rest of the string.  Every machine with memory protection I've seen
 290                  * does it on word boundaries, so is OK with this.  But VALGRIND will
 291                  * still catch it and complain.  The masking trick does make the hash
 292                  * noticably faster for short strings (like English words).
 293                  */
 294 #ifndef VALGRIND
 295
 296                 switch (length) {
 297                 case 12: c+=k[2]; b+=k[1]; a+=k[0]; break;
 298                 case 11: c+=k[2]&0xffffff; b+=k[1]; a+=k[0]; break;
 299                 case 10: c+=k[2]&0xffff; b+=k[1]; a+=k[0]; break;
 300                 case 9 : c+=k[2]&0xff; b+=k[1]; a+=k[0]; break;
 301                 case 8 : b+=k[1]; a+=k[0]; break;
 302                 case 7 : b+=k[1]&0xffffff; a+=k[0]; break;
 303                 case 6 : b+=k[1]&0xffff; a+=k[0]; break;
 304                 case 5 : b+=k[1]&0xff; a+=k[0]; break;
 305                 case 4 : a+=k[0]; break;
 306                 case 3 : a+=k[0]&0xffffff; break;
 307                 case 2 : a+=k[0]&0xffff; break;
 308                 case 1 : a+=k[0]&0xff; break;
 309                 case 0 : return c;              /* zero length strings require no mixing */
 310                 }
 311 #else /* make valgrind happy */
 312                 const uint8_t *k8;
 313
 314                 k8 = (const uint8_t *)k;
 315                 switch (length) {
 316                 case 12: c+=k[2]; b+=k[1]; a+=k[0]; break;
 317                 case 11: c+=((uint32_t)k8[10])<<16;  /* fall through */
 318                 case 10: c+=((uint32_t)k8[9])<<8;    /* fall through */
 319                 case 9 : c+=k8[8];                   /* fall through */
 320                 case 8 : b+=k[1]; a+=k[0]; break;
 321                 case 7 : b+=((uint32_t)k8[6])<<16;   /* fall through */
 322                 case 6 : b+=((uint32_t)k8[5])<<8;    /* fall through */
 323                 case 5 : b+=k8[4];                   /* fall through */
 324                 case 4 : a+=k[0]; break;
 325                 case 3 : a+=((uint32_t)k8[2])<<16;   /* fall through */
 326                 case 2 : a+=((uint32_t)k8[1])<<8;    /* fall through */
 327                 case 1 : a+=k8[0]; break;
 328                 case 0 : return c;
 329                 }
 330 #endif /* !valgrind */
 331         } else if (HASH_LITTLE_ENDIAN && ((u.i & 0x1) == 0)) {
 332                 const uint16_t *k = (const uint16_t *)key;         /* read 16-bit chunks */
 333                 const uint8_t *k8;
 334
 335                 /*--------------- all but last block: aligned reads and different mixing */
 336                 while (length > 12) {
 337                         a += k[0] + (((uint32_t)k[1])<<16);
 338                         b += k[2] + (((uint32_t)k[3])<<16);
 339                         c += k[4] + (((uint32_t)k[5])<<16);
 340                         mix(a,b,c);
 341                         length -= 12;
 342                         k += 6;
 343                 }
 344
 345                 k8 = (const uint8_t *)k;
 346                 switch (length) {
 347                 case 12:
 348                         c+=k[4]+(((uint32_t)k[5])<<16);
 349                         b+=k[2]+(((uint32_t)k[3])<<16);
 350                         a+=k[0]+(((uint32_t)k[1])<<16);
 351                         break;
 352                 case 11:
 353                         c+=((uint32_t)k8[10])<<16;     /* fall through */
 354                 case 10:
 355                         c+=k[4];
 356                         b+=k[2]+(((uint32_t)k[3])<<16);
 357                         a+=k[0]+(((uint32_t)k[1])<<16);
 358                         break;
 359                 case 9:
 360                         c+=k8[8];                      /* fall through */
 361                 case 8:
 362                         b+=k[2]+(((uint32_t)k[3])<<16);
 363                         a+=k[0]+(((uint32_t)k[1])<<16);
 364                         break;
 365                 case 7:
 366                         b+=((uint32_t)k8[6])<<16;      /* fall through */
 367                 case 6:
 368                         b+=k[2];
 369                         a+=k[0]+(((uint32_t)k[1])<<16);
 370                         break;
 371                 case 5:
 372                         b+=k8[4];                      /* fall through */
 373                 case 4:
 374                         a+=k[0]+(((uint32_t)k[1])<<16);
 375                         break;
 376                 case 3:
 377                         a+=((uint32_t)k8[2])<<16;      /* fall through */
 378                 case 2:
 379                         a+=k[0];
 380                         break;
 381                 case 1:
 382                         a+=k8[0];
 383                         break;
 384                 case 0:
 385                         return c;   /* zero length requires no mixing */
 386                 }
 387
 388         } else {    /* need to read the key one byte at a time */
 389                 const uint8_t *k = (const uint8_t *)key;
 390
 391                 while (length > 12) {
 392                         a += k[0];
 393                         a += ((uint32_t)k[1])<<8;
 394                         a += ((uint32_t)k[2])<<16;
 395                         a += ((uint32_t)k[3])<<24;
 396                         b += k[4];
 397                         b += ((uint32_t)k[5])<<8;
 398                         b += ((uint32_t)k[6])<<16;
 399                         b += ((uint32_t)k[7])<<24;
 400                         c += k[8];
 401                         c += ((uint32_t)k[9])<<8;
 402                         c += ((uint32_t)k[10])<<16;
 403                         c += ((uint32_t)k[11])<<24;
 404                         mix(a,b,c);
 405                         length -= 12;
 406                         k += 12;
 407                 }
 408
 409                 switch(length) {                  /* all the case statements fall through */
 410                 case 12: c+=((uint32_t)k[11])<<24;
 411                 case 11: c+=((uint32_t)k[10])<<16;
 412                 case 10: c+=((uint32_t)k[9])<<8;
 413                 case 9: c+=k[8];
 414                 case 8: b+=((uint32_t)k[7])<<24;
 415                 case 7: b+=((uint32_t)k[6])<<16;
 416                 case 6: b+=((uint32_t)k[5])<<8;
 417                 case 5: b+=k[4];
 418                 case 4: a+=((uint32_t)k[3])<<24;
 419                 case 3: a+=((uint32_t)k[2])<<16;
 420                 case 2: a+=((uint32_t)k[1])<<8;
 421                 case 1:
 422                         a+=k[0];
 423                         break;
 424                 case 0:
 425                         return c;
 426                 }
 427         }
 428
 429         final(a,b,c);
 430         return c;
 431 }
 432
 433 #if (CAA_BITS_PER_LONG == 64)
 434 /*
 435  * Hash function for number value.
 436  */
 437 unsigned long hash_key_ulong(void *_key, unsigned long seed)
 438 {
 439         union {
 440                 uint64_t v64;
 441                 uint32_t v32[2];
 442         } v;
 443         union {
 444                 uint64_t v64;
 445                 uint32_t v32[2];
 446         } key;
 447
 448         v.v64 = (uint64_t) seed;
 449         key.v64 = (uint64_t) _key;
 450         hashword2(key.v32, 2, &v.v32[0], &v.v32[1]);
 451         return v.v64;
 452 }
 453 #else
 454 /*
 455  * Hash function for number value.
 456  */
 457 unsigned long hash_key_ulong(void *_key, unsigned long seed)
 458 {
 459         uint32_t key = (uint32_t) _key;
 460
 461         return hashword(&key, 1, seed);
 462 }
 463 #endif /* CAA_BITS_PER_LONG */
 464
 465 /*
 466  * Hash function for string.
 467  */
 468 unsigned long hash_key_str(void *key, unsigned long seed)
 469 {
 470         return hashlittle(key, strlen((char *) key), seed);
 471 }
 472
 473 /*
 474  * Hash function compare for number value.
 475  */
 476 int hash_match_key_ulong(void *key1, void *key2)
 477 {
 478         if (key1 == key2) {
 479                 return 1;
 480         }
 481
 482         return 0;
 483 }
 484
 485 /*
 486  * Hash compare function for string.
 487  */
 488 int hash_match_key_str(void *key1, void *key2)
 489 {
 490         if (strcmp(key1, key2) == 0) {
 491                 return 1;
 492         }
 493
 494         return 0;
 495 }