lib/skiplist.c

   1 /*
   2  * Copyright 1990 William Pugh
   3  *
   4  * Redistribution and use in source and binary forms, with or without
   5  * modification, are permitted.
   6  *
   7  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS''
   8  * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
   9  * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
  10  * PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR
  11  * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  12  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  13  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
  14  * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
  15  * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
  16  * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
  17  * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  18  * SUCH DAMAGE.
  19  *
  20  * Permission to include in quagga provide on March 31, 2016
  21  */
  22
  23 /*
  24  * Skip List impementation based on code from William Pugh.
  25  * ftp://ftp.cs.umd.edu/pub/skipLists/
  26  *
  27  * Skip Lists are a probabilistic alternative to balanced trees, as
  28  * described in the June 1990 issue of CACM and were invented by
  29  * William Pugh in 1987.
  30  *
  31  * This file contains source code to implement a dictionary using
  32  * skip lists and a test driver to test the routines.
  33  *
  34  * A couple of comments about this implementation:
  35  *   The routine randomLevel has been hard-coded to generate random
  36  *   levels using p=0.25. It can be easily changed.
  37  *
  38  *   The insertion routine has been implemented so as to use the
  39  *   dirty hack described in the CACM paper: if a random level is
  40  *   generated that is more than the current maximum level, the
  41  *   current maximum level plus one is used instead.
  42  *
  43  *   Levels start at zero and go up to MaxLevel (which is equal to
  44  *      (MaxNumberOfLevels-1).
  45  *
  46  * The run-time flag SKIPLIST_FLAG_ALLOW_DUPLICATES determines whether or
  47  * not duplicates are allowed for a given list. If set, duplicates are
  48  * allowed and act in a FIFO manner. If not set, an insertion of a value
  49  * already in the list updates the previously existing binding.
  50  *
  51  * BitsInRandom is defined to be the number of bits returned by a call to
  52  * random(). For most all machines with 32-bit integers, this is 31 bits
  53  * as currently set.
  54  */
  55
  56
  57 #include <zebra.h>
  58
  59 #include "memory.h"
  60 #include "log.h"
  61 #include "vty.h"
  62 #include "skiplist.h"
  63 #include "lib_errors.h"
  64 #include "network.h"
  65
  66 DEFINE_MTYPE_STATIC(LIB, SKIP_LIST, "Skip List");
  67 DEFINE_MTYPE_STATIC(LIB, SKIP_LIST_NODE, "Skip Node");
  68
  69 #define BitsInRandom 31
  70
  71 #define MaxNumberOfLevels 16
  72 #define MaxLevel (MaxNumberOfLevels-1)
  73 #define newNodeOfLevel(l) XCALLOC(MTYPE_SKIP_LIST_NODE, sizeof(struct skiplistnode)+(l)*sizeof(struct skiplistnode *))
  74
  75 static int randomsLeft;
  76 static int randomBits;
  77
  78 #if 1
  79 #define CHECKLAST(sl)                                                          \
  80         do {                                                                   \
  81                 if ((sl)->header->forward[0] && !(sl)->last)                   \
  82                         assert(0);                                             \
  83                 if (!(sl)->header->forward[0] && (sl)->last)                   \
  84                         assert(0);                                             \
  85         } while (0)
  86 #else
  87 #define CHECKLAST(sl)
  88 #endif
  89
  90
  91 static int randomLevel(void)
  92 {
  93         register int level = 0;
  94         register int b;
  95
  96         do {
  97                 if (randomsLeft <= 0) {
  98                         randomBits = frr_weak_random();
  99                         randomsLeft = BitsInRandom / 2;
 100                 }
 101                 b = randomBits & 3;
 102                 randomBits >>= 2;
 103                 --randomsLeft;
 104
 105                 if (!b) {
 106                         level++;
 107                         if (level >= MaxLevel)
 108                                 return MaxLevel;
 109                 }
 110         } while (!b);
 111
 112         return level;
 113 }
 114
 115 static int default_cmp(const void *key1, const void *key2)
 116 {
 117         if (key1 < key2)
 118                 return -1;
 119         if (key1 > key2)
 120                 return 1;
 121         return 0;
 122 }
 123
 124 unsigned int skiplist_count(struct skiplist *l)
 125 {
 126         return l->count;
 127 }
 128
 129 struct skiplist *skiplist_new(int flags,
 130                               int (*cmp)(const void *key1, const void *key2),
 131                               void (*del)(void *val))
 132 {
 133         struct skiplist *new;
 134
 135         new = XCALLOC(MTYPE_SKIP_LIST, sizeof(struct skiplist));
 136         assert(new);
 137
 138         new->level = 0;
 139         new->count = 0;
 140         new->header = newNodeOfLevel(MaxNumberOfLevels);
 141         new->stats = newNodeOfLevel(MaxNumberOfLevels);
 142
 143         new->flags = flags;
 144         if (cmp)
 145                 new->cmp = cmp;
 146         else
 147                 new->cmp = default_cmp;
 148
 149         if (del)
 150                 new->del = del;
 151
 152         return new;
 153 }
 154
 155 void skiplist_free(struct skiplist *l)
 156 {
 157         register struct skiplistnode *p, *q;
 158
 159         p = l->header;
 160
 161         do {
 162                 q = p->forward[0];
 163                 if (l->del && p != l->header)
 164                         (*l->del)(p->value);
 165                 XFREE(MTYPE_SKIP_LIST_NODE, p);
 166                 p = q;
 167         } while (p);
 168
 169         XFREE(MTYPE_SKIP_LIST_NODE, l->stats);
 170         XFREE(MTYPE_SKIP_LIST, l);
 171 }
 172
 173
 174 int skiplist_insert(register struct skiplist *l, register void *key,
 175                     register void *value)
 176 {
 177         register int k;
 178         struct skiplistnode *update[MaxNumberOfLevels];
 179         register struct skiplistnode *p, *q;
 180
 181         CHECKLAST(l);
 182
 183         /* DEBUG */
 184         if (!key) {
 185                 flog_err(EC_LIB_DEVELOPMENT, "%s: key is 0, value is %p",
 186                          __func__, value);
 187         }
 188
 189         p = l->header;
 190         k = l->level;
 191         do {
 192                 while (q = p->forward[k], q && (*l->cmp)(q->key, key) < 0)
 193                         p = q;
 194                 update[k] = p;
 195         } while (--k >= 0);
 196
 197         if (!(l->flags & SKIPLIST_FLAG_ALLOW_DUPLICATES) && q
 198             && ((*l->cmp)(q->key, key) == 0)) {
 199
 200                 return -1;
 201         }
 202
 203         k = randomLevel();
 204         assert(k >= 0);
 205         if (k > l->level) {
 206                 k = ++l->level;
 207                 update[k] = l->header;
 208         }
 209
 210         q = newNodeOfLevel(k);
 211         q->key = key;
 212         q->value = value;
 213 #ifdef SKIPLIST_0TIMER_DEBUG
 214         q->flags = SKIPLIST_NODE_FLAG_INSERTED; /* debug */
 215 #endif
 216
 217         ++(l->stats->forward[k]);
 218 #ifdef SKIPLIST_DEBUG
 219         zlog_debug("%s: incremented stats @%p:%d, now %ld", __func__, l, k,
 220                    l->stats->forward[k] - (struct skiplistnode *)NULL);
 221 #endif
 222
 223         do {
 224                 p = update[k];
 225                 q->forward[k] = p->forward[k];
 226                 p->forward[k] = q;
 227         } while (--k >= 0);
 228
 229         /*
 230          * If this is the last item in the list, update the "last" pointer
 231          */
 232         if (!q->forward[0]) {
 233                 l->last = q;
 234         }
 235
 236         ++(l->count);
 237
 238         CHECKLAST(l);
 239
 240         return 0;
 241 }
 242
 243 int skiplist_delete(register struct skiplist *l, register void *key,
 244                     register void *value) /* used only if duplicates allowed */
 245 {
 246         register int k, m;
 247         struct skiplistnode *update[MaxNumberOfLevels];
 248         register struct skiplistnode *p, *q;
 249
 250         CHECKLAST(l);
 251
 252         /* to make debugging easier */
 253         for (k = 0; k < MaxNumberOfLevels; ++k)
 254                 update[k] = NULL;
 255
 256         p = l->header;
 257         k = m = l->level;
 258         do {
 259                 while (q = p->forward[k], q && (*l->cmp)(q->key, key) < 0)
 260                         p = q;
 261                 update[k] = p;
 262         } while (--k >= 0);
 263
 264         if (l->flags & SKIPLIST_FLAG_ALLOW_DUPLICATES) {
 265                 while (q && ((*l->cmp)(q->key, key) == 0)
 266                        && (q->value != value)) {
 267                         int i;
 268                         for (i = 0; i <= l->level; ++i) {
 269                                 if (update[i]->forward[i] == q)
 270                                         update[i] = q;
 271                         }
 272                         q = q->forward[0];
 273                 }
 274         }
 275
 276         if (q && (*l->cmp)(q->key, key) == 0) {
 277                 if (!(l->flags & SKIPLIST_FLAG_ALLOW_DUPLICATES)
 278                     || (q->value == value)) {
 279
 280 /*
 281  * found node to delete
 282  */
 283 #ifdef SKIPLIST_0TIMER_DEBUG
 284                         q->flags &= ~SKIPLIST_NODE_FLAG_INSERTED;
 285 #endif
 286                         /*
 287                          * If we are deleting the last element of the list,
 288                          * update the list's "last" pointer.
 289                          */
 290                         if (l->last == q) {
 291                                 if (update[0] == l->header)
 292                                         l->last = NULL;
 293                                 else
 294                                         l->last = update[0];
 295                         }
 296
 297                         for (k = 0; k <= m && (p = update[k])->forward[k] == q;
 298                              k++) {
 299                                 p->forward[k] = q->forward[k];
 300                         }
 301                         --(l->stats->forward[k - 1]);
 302 #ifdef SKIPLIST_DEBUG
 303                         zlog_debug("%s: decremented stats @%p:%d, now %ld",
 304                                    __func__, l, k - 1,
 305                                    l->stats->forward[k - 1]
 306                                            - (struct skiplistnode *)NULL);
 307 #endif
 308                         if (l->del)
 309                                 (*l->del)(q->value);
 310                         XFREE(MTYPE_SKIP_LIST_NODE, q);
 311                         while (l->header->forward[m] == NULL && m > 0)
 312                                 m--;
 313                         l->level = m;
 314                         CHECKLAST(l);
 315                         --(l->count);
 316                         return 0;
 317                 }
 318         }
 319
 320         CHECKLAST(l);
 321         return -1;
 322 }
 323
 324 /*
 325  * Obtain first value matching "key". Unless SKIPLIST_FLAG_ALLOW_DUPLICATES
 326  * is set, this will also be the only value matching "key".
 327  *
 328  * Also set a cursor for use with skiplist_next_value.
 329  */
 330 int skiplist_first_value(register struct skiplist *l, /* in */
 331                          register const void *key,    /* in */
 332                          void **valuePointer,         /* out */
 333                          void **cursor)               /* out */
 334 {
 335         register int k;
 336         register struct skiplistnode *p, *q;
 337
 338         p = l->header;
 339         k = l->level;
 340
 341         do {
 342                 while (q = p->forward[k], q && (*l->cmp)(q->key, key) < 0)
 343                         p = q;
 344
 345         } while (--k >= 0);
 346
 347         if (!q || (*l->cmp)(q->key, key))
 348                 return -1;
 349
 350         if (valuePointer)
 351                 *valuePointer = q->value;
 352
 353         if (cursor)
 354                 *cursor = q;
 355
 356         return 0;
 357 }
 358
 359 int skiplist_search(register struct skiplist *l, register void *key,
 360                     void **valuePointer)
 361 {
 362         return skiplist_first_value(l, key, valuePointer, NULL);
 363 }
 364
 365
 366 /*
 367  * Caller supplies key and value of an existing item in the list.
 368  * Function returns the value of the next list item that has the
 369  * same key (useful when SKIPLIST_FLAG_ALLOW_DUPLICATES is set).
 370  *
 371  * Returns 0 on success. If the caller-supplied key and value
 372  * do not correspond to a list element, or if they specify the
 373  * last element with the given key, -1 is returned.
 374  */
 375 int skiplist_next_value(register struct skiplist *l, /* in */
 376                         register const void *key,         /* in */
 377                         void **valuePointer,     /* in/out */
 378                         void **cursor)               /* in/out */
 379 {
 380         register int k;
 381         register struct skiplistnode *p, *q;
 382
 383         CHECKLAST(l);
 384
 385         if (!(l->flags & SKIPLIST_FLAG_ALLOW_DUPLICATES)) {
 386                 return -1;
 387         }
 388
 389         if (!cursor || !*cursor) {
 390                 p = l->header;
 391                 k = l->level;
 392
 393                 /*
 394                  * Find matching key
 395                  */
 396                 do {
 397                         while (q = p->forward[k],
 398                                q && (*l->cmp)(q->key, key) < 0)
 399                                 p = q;
 400                 } while (--k >= 0);
 401
 402                 /*
 403                  * Find matching value
 404                  */
 405                 while (q && ((*l->cmp)(q->key, key) == 0)
 406                        && (q->value != *valuePointer)) {
 407                         q = q->forward[0];
 408                 }
 409
 410                 if (!q || ((*l->cmp)(q->key, key) != 0)
 411                     || (q->value != *valuePointer)) {
 412                         /*
 413                          * No matching value
 414                          */
 415                         CHECKLAST(l);
 416                         return -1;
 417                 }
 418         } else {
 419                 q = (struct skiplistnode *)*cursor;
 420         }
 421
 422         /*
 423          * Advance cursor
 424          */
 425         q = q->forward[0];
 426
 427         /*
 428          * If we reached end-of-list or if the key is no longer the same,
 429          * then return error
 430          */
 431         if (!q || ((*l->cmp)(q->key, key) != 0))
 432                 return -1;
 433
 434         *valuePointer = q->value;
 435         if (cursor)
 436                 *cursor = q;
 437         CHECKLAST(l);
 438         return 0;
 439 }
 440
 441 int skiplist_first(register struct skiplist *l, void **keyPointer,
 442                    void **valuePointer)
 443 {
 444         register struct skiplistnode *p;
 445
 446         CHECKLAST(l);
 447         p = l->header->forward[0];
 448         if (!p)
 449                 return -1;
 450
 451         if (keyPointer)
 452                 *keyPointer = p->key;
 453
 454         if (valuePointer)
 455                 *valuePointer = p->value;
 456
 457         CHECKLAST(l);
 458
 459         return 0;
 460 }
 461
 462 int skiplist_last(register struct skiplist *l, void **keyPointer,
 463                   void **valuePointer)
 464 {
 465         CHECKLAST(l);
 466         if (l->last) {
 467                 if (keyPointer)
 468                         *keyPointer = l->last->key;
 469                 if (valuePointer)
 470                         *valuePointer = l->last->value;
 471                 return 0;
 472         }
 473         return -1;
 474 }
 475
 476 /*
 477  * true = empty
 478  */
 479 int skiplist_empty(register struct skiplist *l)
 480 {
 481         CHECKLAST(l);
 482         if (l->last)
 483                 return 0;
 484         return 1;
 485 }
 486
 487 /*
 488  * Use this to walk the list. Caller sets *cursor to NULL to obtain
 489  * first element. Return value of 0 indicates valid cursor/element
 490  * returned, otherwise NULL cursor arg or EOL.
 491  */
 492 int skiplist_next(register struct skiplist *l, /* in */
 493                   void **keyPointer,       /* out */
 494                   void **valuePointer,   /* out */
 495                   void **cursor)               /* in/out */
 496 {
 497         struct skiplistnode *p;
 498
 499         if (!cursor)
 500                 return -1;
 501
 502         CHECKLAST(l);
 503
 504         if (!*cursor) {
 505                 p = l->header->forward[0];
 506         } else {
 507                 p = *cursor;
 508                 p = p->forward[0];
 509         }
 510         *cursor = p;
 511
 512         if (!p)
 513                 return -1;
 514
 515         if (keyPointer)
 516                 *keyPointer = p->key;
 517
 518         if (valuePointer)
 519                 *valuePointer = p->value;
 520
 521         CHECKLAST(l);
 522
 523         return 0;
 524 }
 525
 526 int skiplist_delete_first(register struct skiplist *l)
 527 {
 528         register int k;
 529         register struct skiplistnode *p, *q;
 530         int nodelevel = 0;
 531
 532         CHECKLAST(l);
 533
 534         p = l->header;
 535         q = l->header->forward[0];
 536
 537         if (!q)
 538                 return -1;
 539
 540         for (k = l->level; k >= 0; --k) {
 541                 if (p->forward[k] == q) {
 542                         p->forward[k] = q->forward[k];
 543                         if ((k == l->level) && (p->forward[k] == NULL)
 544                             && (l->level > 0))
 545                                 --(l->level);
 546                         if (!nodelevel)
 547                                 nodelevel = k;
 548                 }
 549         }
 550
 551 #ifdef SKIPLIST_0TIMER_DEBUG
 552         q->flags &= ~SKIPLIST_NODE_FLAG_INSERTED;
 553 #endif
 554         /*
 555          * If we are deleting the last element of the list,
 556          * update the list's "last" pointer.
 557          */
 558         if (l->last == q) {
 559                 l->last = NULL;
 560         }
 561
 562         --(l->stats->forward[nodelevel]);
 563 #ifdef SKIPLIST_DEBUG
 564         zlog_debug("%s: decremented stats @%p:%d, now %ld", __func__, l,
 565                    nodelevel,
 566                    l->stats->forward[nodelevel] - (struct skiplistnode *)NULL);
 567 #endif
 568
 569         if (l->del)
 570                 (*l->del)(q->value);
 571
 572         XFREE(MTYPE_SKIP_LIST_NODE, q);
 573
 574         CHECKLAST(l);
 575
 576         --(l->count);
 577
 578         return 0;
 579 }
 580
 581 void skiplist_debug(struct vty *vty, struct skiplist *l)
 582 {
 583         int i;
 584
 585         if (!l)
 586                 return;
 587
 588         vty_out(vty, "Skiplist %p has max level %d\n", l, l->level);
 589         for (i = l->level; i >= 0; --i)
 590                 vty_out(vty, "  @%d: %ld\n", i,
 591                         (long)((l->stats->forward[i])
 592                                - (struct skiplistnode *)NULL));
 593 }
 594
 595 static void *scramble(int i)
 596 {
 597         uintptr_t result;
 598
 599         result = (unsigned)(i & 0xff) << 24;
 600         result |= (unsigned)i >> 8;
 601
 602         return (void *)result;
 603 }
 604
 605 #define sampleSize 65536
 606 void skiplist_test(struct vty *vty)
 607 {
 608         struct skiplist *l;
 609         register int i, k;
 610         void *keys[sampleSize];
 611         void *v = NULL;
 612
 613         zlog_debug("%s: entry", __func__);
 614
 615         l = skiplist_new(SKIPLIST_FLAG_ALLOW_DUPLICATES, NULL, NULL);
 616
 617         zlog_debug("%s: skiplist_new returned %p", __func__, l);
 618
 619         for (i = 0; i < 4; i++) {
 620
 621                 for (k = 0; k < sampleSize; k++) {
 622                         if (!(k % 1000)) {
 623                                 zlog_debug("%s: (%d:%d)", __func__, i, k);
 624                         }
 625                         // keys[k] = (void *)random();
 626                         keys[k] = scramble(k);
 627                         if (skiplist_insert(l, keys[k], keys[k]))
 628                                 zlog_debug("error in insert #%d,#%d", i, k);
 629                 }
 630
 631                 zlog_debug("%s: inserts done", __func__);
 632
 633                 for (k = 0; k < sampleSize; k++) {
 634
 635                         if (!(k % 1000))
 636                                 zlog_debug("[%d:%d]", i, k);
 637                         if (skiplist_search(l, keys[k], &v))
 638                                 zlog_debug("error in search #%d,#%d", i, k);
 639
 640                         if (v != keys[k])
 641                                 zlog_debug("search returned wrong value");
 642                 }
 643
 644
 645                 for (k = 0; k < sampleSize; k++) {
 646
 647                         if (!(k % 1000))
 648                                 zlog_debug("<%d:%d>", i, k);
 649                         if (skiplist_delete(l, keys[k], keys[k]))
 650                                 zlog_debug("error in delete");
 651                         keys[k] = scramble(k ^ 0xf0f0f0f0);
 652                         if (skiplist_insert(l, keys[k], keys[k]))
 653                                 zlog_debug("error in insert #%d,#%d", i, k);
 654                 }
 655
 656                 for (k = 0; k < sampleSize; k++) {
 657
 658                         if (!(k % 1000))
 659                                 zlog_debug("{%d:%d}", i, k);
 660                         if (skiplist_delete_first(l))
 661                                 zlog_debug("error in delete_first");
 662                 }
 663         }
 664
 665         skiplist_free(l);
 666 }