src/uobject/avl.c

   1 /* Produced by texiweb from libavl.w. */
   2
   3 /* libavl - library for manipulation of binary trees.
   4    Copyright (C) 1998, 1999, 2000, 2001, 2002, 2004 Free Software
   5    Foundation, Inc.
   6
   7    This library is free software; you can redistribute it and/or
   8    modify it under the terms of the GNU Lesser General Public
   9    License as published by the Free Software Foundation; either
  10    version 3 of the License, or (at your option) any later version.
  11
  12    This library is distributed in the hope that it will be useful,
  13    but WITHOUT ANY WARRANTY; without even the implied warranty of
  14    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  15    Lesser General Public License for more details.
  16
  17    You should have received a copy of the GNU Lesser General Public
  18    License along with this library; if not, write to the Free Software
  19    Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
  20    02110-1301 USA.
  21 */
  22
  23 #include <config.h>
  24 #include <assert.h>
  25 #include <stdio.h>
  26 #include <stdlib.h>
  27 #include <string.h>
  28 #include "avl.h"
  29
  30 /* Creates and returns a new table
  31    with comparison function |compare| using parameter |param|
  32    and memory allocator |allocator|.
  33    Returns |NULL| if memory allocation failed. */
  34 struct avl_table *
  35 avl_create (avl_comparison_func *compare, void *param,
  36             struct libavl_allocator *allocator)
  37 {
  38   struct avl_table *tree;
  39
  40   assert (compare != NULL);
  41
  42   if (allocator == NULL)
  43     allocator = &avl_allocator_default;
  44
  45   tree = allocator->libavl_malloc (allocator, sizeof *tree);
  46   if (tree == NULL)
  47     return NULL;
  48
  49   tree->avl_root = NULL;
  50   tree->avl_compare = compare;
  51   tree->avl_param = param;
  52   tree->avl_alloc = allocator;
  53   tree->avl_count = 0;
  54   tree->avl_generation = 0;
  55
  56   return tree;
  57 }
  58
  59 /* Search |tree| for an item matching |item|, and return it if found.
  60    Otherwise return |NULL|. */
  61 void *
  62 avl_find (const struct avl_table *tree, const void *item)
  63 {
  64   const struct avl_node *p;
  65
  66   assert (tree != NULL && item != NULL);
  67   for (p = tree->avl_root; p != NULL; )
  68     {
  69       int cmp = tree->avl_compare (item, p->avl_data, tree->avl_param);
  70
  71       if (cmp < 0)
  72         p = p->avl_link[0];
  73       else if (cmp > 0)
  74         p = p->avl_link[1];
  75       else /* |cmp == 0| */
  76         return p->avl_data;
  77     }
  78
  79   return NULL;
  80 }
  81
  82 /* Inserts |item| into |tree| and returns a pointer to |item|'s address.
  83    If a duplicate item is found in the tree,
  84    returns a pointer to the duplicate without inserting |item|.
  85    Returns |NULL| in case of memory allocation failure. */
  86 void **
  87 avl_probe (struct avl_table *tree, void *item)
  88 {
  89   struct avl_node *y, *z; /* Top node to update balance factor, and parent. */
  90   struct avl_node *p, *q; /* Iterator, and parent. */
  91   struct avl_node *n;     /* Newly inserted node. */
  92   struct avl_node *w;     /* New root of rebalanced subtree. */
  93   int dir;                /* Direction to descend. */
  94
  95   unsigned char da[AVL_MAX_HEIGHT]; /* Cached comparison results. */
  96   int k = 0;              /* Number of cached results. */
  97
  98   assert (tree != NULL && item != NULL);
  99
 100   z = (struct avl_node *) &tree->avl_root;
 101   y = tree->avl_root;
 102   dir = 0;
 103   for (q = z, p = y; p != NULL; q = p, p = p->avl_link[dir])
 104     {
 105       int cmp = tree->avl_compare (item, p->avl_data, tree->avl_param);
 106       if (cmp == 0)
 107         return &p->avl_data;
 108
 109       if (p->avl_balance != 0)
 110         z = q, y = p, k = 0;
 111       da[k++] = dir = cmp > 0;
 112     }
 113
 114   n = q->avl_link[dir] =
 115     tree->avl_alloc->libavl_malloc (tree->avl_alloc, sizeof *n);
 116   if (n == NULL)
 117     return NULL;
 118
 119   tree->avl_count++;
 120   n->avl_data = item;
 121   n->avl_link[0] = n->avl_link[1] = NULL;
 122   n->avl_balance = 0;
 123   if (y == NULL)
 124     return &n->avl_data;
 125
 126   for (p = y, k = 0; p != n; p = p->avl_link[da[k]], k++)
 127     if (da[k] == 0)
 128       p->avl_balance--;
 129     else
 130       p->avl_balance++;
 131
 132   if (y->avl_balance == -2)
 133     {
 134       struct avl_node *x = y->avl_link[0];
 135       if (x->avl_balance == -1)
 136         {
 137           w = x;
 138           y->avl_link[0] = x->avl_link[1];
 139           x->avl_link[1] = y;
 140           x->avl_balance = y->avl_balance = 0;
 141         }
 142       else
 143         {
 144           assert (x->avl_balance == +1);
 145           w = x->avl_link[1];
 146           x->avl_link[1] = w->avl_link[0];
 147           w->avl_link[0] = x;
 148           y->avl_link[0] = w->avl_link[1];
 149           w->avl_link[1] = y;
 150           if (w->avl_balance == -1)
 151             x->avl_balance = 0, y->avl_balance = +1;
 152           else if (w->avl_balance == 0)
 153             x->avl_balance = y->avl_balance = 0;
 154           else /* |w->avl_balance == +1| */
 155             x->avl_balance = -1, y->avl_balance = 0;
 156           w->avl_balance = 0;
 157         }
 158     }
 159   else if (y->avl_balance == +2)
 160     {
 161       struct avl_node *x = y->avl_link[1];
 162       if (x->avl_balance == +1)
 163         {
 164           w = x;
 165           y->avl_link[1] = x->avl_link[0];
 166           x->avl_link[0] = y;
 167           x->avl_balance = y->avl_balance = 0;
 168         }
 169       else
 170         {
 171           assert (x->avl_balance == -1);
 172           w = x->avl_link[0];
 173           x->avl_link[0] = w->avl_link[1];
 174           w->avl_link[1] = x;
 175           y->avl_link[1] = w->avl_link[0];
 176           w->avl_link[0] = y;
 177           if (w->avl_balance == +1)
 178             x->avl_balance = 0, y->avl_balance = -1;
 179           else if (w->avl_balance == 0)
 180             x->avl_balance = y->avl_balance = 0;
 181           else /* |w->avl_balance == -1| */
 182             x->avl_balance = +1, y->avl_balance = 0;
 183           w->avl_balance = 0;
 184         }
 185     }
 186   else
 187     return &n->avl_data;
 188   z->avl_link[y != z->avl_link[0]] = w;
 189
 190   tree->avl_generation++;
 191   return &n->avl_data;
 192 }
 193
 194 /* Inserts |item| into |table|.
 195    Returns |NULL| if |item| was successfully inserted
 196    or if a memory allocation error occurred.
 197    Otherwise, returns the duplicate item. */
 198 void *
 199 avl_insert (struct avl_table *table, void *item)
 200 {
 201   void **p = avl_probe (table, item);
 202   return p == NULL || *p == item ? NULL : *p;
 203 }
 204
 205 /* Inserts |item| into |table|, replacing any duplicate item.
 206    Returns |NULL| if |item| was inserted without replacing a duplicate,
 207    or if a memory allocation error occurred.
 208    Otherwise, returns the item that was replaced. */
 209 void *
 210 avl_replace (struct avl_table *table, void *item)
 211 {
 212   void **p = avl_probe (table, item);
 213   if (p == NULL || *p == item)
 214     return NULL;
 215   else
 216     {
 217       void *r = *p;
 218       *p = item;
 219       return r;
 220     }
 221 }
 222
 223 /* Deletes from |tree| and returns an item matching |item|.
 224    Returns a null pointer if no matching item found. */
 225 void *
 226 avl_delete (struct avl_table *tree, const void *item)
 227 {
 228   /* Stack of nodes. */
 229   struct avl_node *pa[AVL_MAX_HEIGHT]; /* Nodes. */
 230   unsigned char da[AVL_MAX_HEIGHT];    /* |avl_link[]| indexes. */
 231   int k;                               /* Stack pointer. */
 232
 233   struct avl_node *p;   /* Traverses tree to find node to delete. */
 234   int cmp;              /* Result of comparison between |item| and |p|. */
 235
 236   assert (tree != NULL && item != NULL);
 237
 238   k = 0;
 239   p = (struct avl_node *) &tree->avl_root;
 240   for (cmp = -1; cmp != 0;
 241        cmp = tree->avl_compare (item, p->avl_data, tree->avl_param))
 242     {
 243       int dir = cmp > 0;
 244
 245       pa[k] = p;
 246       da[k++] = dir;
 247
 248       p = p->avl_link[dir];
 249       if (p == NULL)
 250         return NULL;
 251     }
 252   item = p->avl_data;
 253
 254   if (p->avl_link[1] == NULL)
 255     pa[k - 1]->avl_link[da[k - 1]] = p->avl_link[0];
 256   else
 257     {
 258       struct avl_node *r = p->avl_link[1];
 259       if (r->avl_link[0] == NULL)
 260         {
 261           r->avl_link[0] = p->avl_link[0];
 262           r->avl_balance = p->avl_balance;
 263           pa[k - 1]->avl_link[da[k - 1]] = r;
 264           da[k] = 1;
 265           pa[k++] = r;
 266         }
 267       else
 268         {
 269           struct avl_node *s;
 270           int j = k++;
 271
 272           for (;;)
 273             {
 274               da[k] = 0;
 275               pa[k++] = r;
 276               s = r->avl_link[0];
 277               if (s->avl_link[0] == NULL)
 278                 break;
 279
 280               r = s;
 281             }
 282
 283           s->avl_link[0] = p->avl_link[0];
 284           r->avl_link[0] = s->avl_link[1];
 285           s->avl_link[1] = p->avl_link[1];
 286           s->avl_balance = p->avl_balance;
 287
 288           pa[j - 1]->avl_link[da[j - 1]] = s;
 289           da[j] = 1;
 290           pa[j] = s;
 291         }
 292     }
 293
 294   tree->avl_alloc->libavl_free (tree->avl_alloc, p);
 295
 296   assert (k > 0);
 297   while (--k > 0)
 298     {
 299       struct avl_node *y = pa[k];
 300
 301       if (da[k] == 0)
 302         {
 303           y->avl_balance++;
 304           if (y->avl_balance == +1)
 305             break;
 306           else if (y->avl_balance == +2)
 307             {
 308               struct avl_node *x = y->avl_link[1];
 309               if (x->avl_balance == -1)
 310                 {
 311                   struct avl_node *w;
 312                   assert (x->avl_balance == -1);
 313                   w = x->avl_link[0];
 314                   x->avl_link[0] = w->avl_link[1];
 315                   w->avl_link[1] = x;
 316                   y->avl_link[1] = w->avl_link[0];
 317                   w->avl_link[0] = y;
 318                   if (w->avl_balance == +1)
 319                     x->avl_balance = 0, y->avl_balance = -1;
 320                   else if (w->avl_balance == 0)
 321                     x->avl_balance = y->avl_balance = 0;
 322                   else /* |w->avl_balance == -1| */
 323                     x->avl_balance = +1, y->avl_balance = 0;
 324                   w->avl_balance = 0;
 325                   pa[k - 1]->avl_link[da[k - 1]] = w;
 326                 }
 327               else
 328                 {
 329                   y->avl_link[1] = x->avl_link[0];
 330                   x->avl_link[0] = y;
 331                   pa[k - 1]->avl_link[da[k - 1]] = x;
 332                   if (x->avl_balance == 0)
 333                     {
 334                       x->avl_balance = -1;
 335                       y->avl_balance = +1;
 336                       break;
 337                     }
 338                   else
 339                     x->avl_balance = y->avl_balance = 0;
 340                 }
 341             }
 342         }
 343       else
 344         {
 345           y->avl_balance--;
 346           if (y->avl_balance == -1)
 347             break;
 348           else if (y->avl_balance == -2)
 349             {
 350               struct avl_node *x = y->avl_link[0];
 351               if (x->avl_balance == +1)
 352                 {
 353                   struct avl_node *w;
 354                   assert (x->avl_balance == +1);
 355                   w = x->avl_link[1];
 356                   x->avl_link[1] = w->avl_link[0];
 357                   w->avl_link[0] = x;
 358                   y->avl_link[0] = w->avl_link[1];
 359                   w->avl_link[1] = y;
 360                   if (w->avl_balance == -1)
 361                     x->avl_balance = 0, y->avl_balance = +1;
 362                   else if (w->avl_balance == 0)
 363                     x->avl_balance = y->avl_balance = 0;
 364                   else /* |w->avl_balance == +1| */
 365                     x->avl_balance = -1, y->avl_balance = 0;
 366                   w->avl_balance = 0;
 367                   pa[k - 1]->avl_link[da[k - 1]] = w;
 368                 }
 369               else
 370                 {
 371                   y->avl_link[0] = x->avl_link[1];
 372                   x->avl_link[1] = y;
 373                   pa[k - 1]->avl_link[da[k - 1]] = x;
 374                   if (x->avl_balance == 0)
 375                     {
 376                       x->avl_balance = +1;
 377                       y->avl_balance = -1;
 378                       break;
 379                     }
 380                   else
 381                     x->avl_balance = y->avl_balance = 0;
 382                 }
 383             }
 384         }
 385     }
 386
 387   tree->avl_count--;
 388   tree->avl_generation++;
 389   return (void *) item;
 390 }
 391
 392 /* Refreshes the stack of parent pointers in |trav|
 393    and updates its generation number. */
 394 static void
 395 trav_refresh (struct avl_traverser *trav)
 396 {
 397   assert (trav != NULL);
 398
 399   trav->avl_generation = trav->avl_table->avl_generation;
 400
 401   if (trav->avl_node != NULL)
 402     {
 403       avl_comparison_func *cmp = trav->avl_table->avl_compare;
 404       void *param = trav->avl_table->avl_param;
 405       struct avl_node *node = trav->avl_node;
 406       struct avl_node *i;
 407
 408       trav->avl_height = 0;
 409       for (i = trav->avl_table->avl_root; i != node; )
 410         {
 411           assert (trav->avl_height < AVL_MAX_HEIGHT);
 412           assert (i != NULL);
 413
 414           trav->avl_stack[trav->avl_height++] = i;
 415           i = i->avl_link[cmp (node->avl_data, i->avl_data, param) > 0];
 416         }
 417     }
 418 }
 419
 420 /* Initializes |trav| for use with |tree|
 421    and selects the null node. */
 422 void
 423 avl_t_init (struct avl_traverser *trav, struct avl_table *tree)
 424 {
 425   trav->avl_table = tree;
 426   trav->avl_node = NULL;
 427   trav->avl_height = 0;
 428   trav->avl_generation = tree->avl_generation;
 429 }
 430
 431 /* Initializes |trav| for |tree|
 432    and selects and returns a pointer to its least-valued item.
 433    Returns |NULL| if |tree| contains no nodes. */
 434 void *
 435 avl_t_first (struct avl_traverser *trav, struct avl_table *tree)
 436 {
 437   struct avl_node *x;
 438
 439   assert (tree != NULL && trav != NULL);
 440
 441   trav->avl_table = tree;
 442   trav->avl_height = 0;
 443   trav->avl_generation = tree->avl_generation;
 444
 445   x = tree->avl_root;
 446   if (x != NULL)
 447     while (x->avl_link[0] != NULL)
 448       {
 449         assert (trav->avl_height < AVL_MAX_HEIGHT);
 450         trav->avl_stack[trav->avl_height++] = x;
 451         x = x->avl_link[0];
 452       }
 453   trav->avl_node = x;
 454
 455   return x != NULL ? x->avl_data : NULL;
 456 }
 457
 458 /* Initializes |trav| for |tree|
 459    and selects and returns a pointer to its greatest-valued item.
 460    Returns |NULL| if |tree| contains no nodes. */
 461 void *
 462 avl_t_last (struct avl_traverser *trav, struct avl_table *tree)
 463 {
 464   struct avl_node *x;
 465
 466   assert (tree != NULL && trav != NULL);
 467
 468   trav->avl_table = tree;
 469   trav->avl_height = 0;
 470   trav->avl_generation = tree->avl_generation;
 471
 472   x = tree->avl_root;
 473   if (x != NULL)
 474     while (x->avl_link[1] != NULL)
 475       {
 476         assert (trav->avl_height < AVL_MAX_HEIGHT);
 477         trav->avl_stack[trav->avl_height++] = x;
 478         x = x->avl_link[1];
 479       }
 480   trav->avl_node = x;
 481
 482   return x != NULL ? x->avl_data : NULL;
 483 }
 484
 485 /* Searches for |item| in |tree|.
 486    If found, initializes |trav| to the item found and returns the item
 487    as well.
 488    If there is no matching item, initializes |trav| to the null item
 489    and returns |NULL|. */
 490 void *
 491 avl_t_find (struct avl_traverser *trav, struct avl_table *tree, void *item)
 492 {
 493   struct avl_node *p, *q;
 494
 495   assert (trav != NULL && tree != NULL && item != NULL);
 496   trav->avl_table = tree;
 497   trav->avl_height = 0;
 498   trav->avl_generation = tree->avl_generation;
 499   for (p = tree->avl_root; p != NULL; p = q)
 500     {
 501       int cmp = tree->avl_compare (item, p->avl_data, tree->avl_param);
 502
 503       if (cmp < 0)
 504         q = p->avl_link[0];
 505       else if (cmp > 0)
 506         q = p->avl_link[1];
 507       else /* |cmp == 0| */
 508         {
 509           trav->avl_node = p;
 510           return p->avl_data;
 511         }
 512
 513       assert (trav->avl_height < AVL_MAX_HEIGHT);
 514       trav->avl_stack[trav->avl_height++] = p;
 515     }
 516
 517   trav->avl_height = 0;
 518   trav->avl_node = NULL;
 519   return NULL;
 520 }
 521
 522 /* Attempts to insert |item| into |tree|.
 523    If |item| is inserted successfully, it is returned and |trav| is
 524    initialized to its location.
 525    If a duplicate is found, it is returned and |trav| is initialized to
 526    its location.  No replacement of the item occurs.
 527    If a memory allocation failure occurs, |NULL| is returned and |trav|
 528    is initialized to the null item. */
 529 void *
 530 avl_t_insert (struct avl_traverser *trav, struct avl_table *tree, void *item)
 531 {
 532   void **p;
 533
 534   assert (trav != NULL && tree != NULL && item != NULL);
 535
 536   p = avl_probe (tree, item);
 537   if (p != NULL)
 538     {
 539       trav->avl_table = tree;
 540       trav->avl_node =
 541         ((struct avl_node *)
 542          ((char *) p - offsetof (struct avl_node, avl_data)));
 543       trav->avl_generation = tree->avl_generation - 1;
 544       return *p;
 545     }
 546   else
 547     {
 548       avl_t_init (trav, tree);
 549       return NULL;
 550     }
 551 }
 552
 553 /* Initializes |trav| to have the same current node as |src|. */
 554 void *
 555 avl_t_copy (struct avl_traverser *trav, const struct avl_traverser *src)
 556 {
 557   assert (trav != NULL && src != NULL);
 558
 559   if (trav != src)
 560     {
 561       trav->avl_table = src->avl_table;
 562       trav->avl_node = src->avl_node;
 563       trav->avl_generation = src->avl_generation;
 564       if (trav->avl_generation == trav->avl_table->avl_generation)
 565         {
 566           trav->avl_height = src->avl_height;
 567           memcpy (trav->avl_stack, (const void *) src->avl_stack,
 568                   sizeof *trav->avl_stack * trav->avl_height);
 569         }
 570     }
 571
 572   return trav->avl_node != NULL ? trav->avl_node->avl_data : NULL;
 573 }
 574
 575 /* Returns the next data item in inorder
 576    within the tree being traversed with |trav|,
 577    or if there are no more data items returns |NULL|. */
 578 void *
 579 avl_t_next (struct avl_traverser *trav)
 580 {
 581   struct avl_node *x;
 582
 583   assert (trav != NULL);
 584
 585   if (trav->avl_generation != trav->avl_table->avl_generation)
 586     trav_refresh (trav);
 587
 588   x = trav->avl_node;
 589   if (x == NULL)
 590     {
 591       return avl_t_first (trav, trav->avl_table);
 592     }
 593   else if (x->avl_link[1] != NULL)
 594     {
 595       assert (trav->avl_height < AVL_MAX_HEIGHT);
 596       trav->avl_stack[trav->avl_height++] = x;
 597       x = x->avl_link[1];
 598
 599       while (x->avl_link[0] != NULL)
 600         {
 601           assert (trav->avl_height < AVL_MAX_HEIGHT);
 602           trav->avl_stack[trav->avl_height++] = x;
 603           x = x->avl_link[0];
 604         }
 605     }
 606   else
 607     {
 608       struct avl_node *y;
 609
 610       do
 611         {
 612           if (trav->avl_height == 0)
 613             {
 614               trav->avl_node = NULL;
 615               return NULL;
 616             }
 617
 618           y = x;
 619           x = trav->avl_stack[--trav->avl_height];
 620         }
 621       while (y == x->avl_link[1]);
 622     }
 623   trav->avl_node = x;
 624
 625   return x->avl_data;
 626 }
 627
 628 /* Returns the previous data item in inorder
 629    within the tree being traversed with |trav|,
 630    or if there are no more data items returns |NULL|. */
 631 void *
 632 avl_t_prev (struct avl_traverser *trav)
 633 {
 634   struct avl_node *x;
 635
 636   assert (trav != NULL);
 637
 638   if (trav->avl_generation != trav->avl_table->avl_generation)
 639     trav_refresh (trav);
 640
 641   x = trav->avl_node;
 642   if (x == NULL)
 643     {
 644       return avl_t_last (trav, trav->avl_table);
 645     }
 646   else if (x->avl_link[0] != NULL)
 647     {
 648       assert (trav->avl_height < AVL_MAX_HEIGHT);
 649       trav->avl_stack[trav->avl_height++] = x;
 650       x = x->avl_link[0];
 651
 652       while (x->avl_link[1] != NULL)
 653         {
 654           assert (trav->avl_height < AVL_MAX_HEIGHT);
 655           trav->avl_stack[trav->avl_height++] = x;
 656           x = x->avl_link[1];
 657         }
 658     }
 659   else
 660     {
 661       struct avl_node *y;
 662
 663       do
 664         {
 665           if (trav->avl_height == 0)
 666             {
 667               trav->avl_node = NULL;
 668               return NULL;
 669             }
 670
 671           y = x;
 672           x = trav->avl_stack[--trav->avl_height];
 673         }
 674       while (y == x->avl_link[0]);
 675     }
 676   trav->avl_node = x;
 677
 678   return x->avl_data;
 679 }
 680
 681 /* Returns |trav|'s current item. */
 682 void *
 683 avl_t_cur (struct avl_traverser *trav)
 684 {
 685   assert (trav != NULL);
 686
 687   return trav->avl_node != NULL ? trav->avl_node->avl_data : NULL;
 688 }
 689
 690 /* Replaces the current item in |trav| by |new| and returns the item replaced.
 691    |trav| must not have the null item selected.
 692    The new item must not upset the ordering of the tree. */
 693 void *
 694 avl_t_replace (struct avl_traverser *trav, void *new)
 695 {
 696   void *old;
 697
 698   assert (trav != NULL && trav->avl_node != NULL && new != NULL);
 699   old = trav->avl_node->avl_data;
 700   trav->avl_node->avl_data = new;
 701   return old;
 702 }
 703
 704 /* Destroys |new| with |avl_destroy (new, destroy)|,
 705    first setting right links of nodes in |stack| within |new|
 706    to null pointers to avoid touching uninitialized data. */
 707 static void
 708 copy_error_recovery (struct avl_node **stack, int height,
 709                      struct avl_table *new, avl_item_func *destroy)
 710 {
 711   assert (stack != NULL && height >= 0 && new != NULL);
 712
 713   for (; height > 2; height -= 2)
 714     stack[height - 1]->avl_link[1] = NULL;
 715   avl_destroy (new, destroy);
 716 }
 717
 718 /* Copies |org| to a newly created tree, which is returned.
 719    If |copy != NULL|, each data item in |org| is first passed to |copy|,
 720    and the return values are inserted into the tree,
 721    with |NULL| return values taken as indications of failure.
 722    On failure, destroys the partially created new tree,
 723    applying |destroy|, if non-null, to each item in the new tree so far,
 724    and returns |NULL|.
 725    If |allocator != NULL|, it is used for allocation in the new tree.
 726    Otherwise, the same allocator used for |org| is used. */
 727 struct avl_table *
 728 avl_copy (const struct avl_table *org, avl_copy_func *copy,
 729           avl_item_func *destroy, struct libavl_allocator *allocator)
 730 {
 731   struct avl_node *stack[2 * (AVL_MAX_HEIGHT + 1)];
 732   int height = 0;
 733
 734   struct avl_table *new;
 735   const struct avl_node *x;
 736   struct avl_node *y;
 737
 738   assert (org != NULL);
 739   new = avl_create (org->avl_compare, org->avl_param,
 740                     allocator != NULL ? allocator : org->avl_alloc);
 741   if (new == NULL)
 742     return NULL;
 743   new->avl_count = org->avl_count;
 744   if (new->avl_count == 0)
 745     return new;
 746
 747   x = (const struct avl_node *) &org->avl_root;
 748   y = (struct avl_node *) &new->avl_root;
 749   for (;;)
 750     {
 751       while (x->avl_link[0] != NULL)
 752         {
 753           assert (height < 2 * (AVL_MAX_HEIGHT + 1));
 754
 755           y->avl_link[0] =
 756             new->avl_alloc->libavl_malloc (new->avl_alloc,
 757                                            sizeof *y->avl_link[0]);
 758           if (y->avl_link[0] == NULL)
 759             {
 760               if (y != (struct avl_node *) &new->avl_root)
 761                 {
 762                   y->avl_data = NULL;
 763                   y->avl_link[1] = NULL;
 764                 }
 765
 766               copy_error_recovery (stack, height, new, destroy);
 767               return NULL;
 768             }
 769
 770           stack[height++] = (struct avl_node *) x;
 771           stack[height++] = y;
 772           x = x->avl_link[0];
 773           y = y->avl_link[0];
 774         }
 775       y->avl_link[0] = NULL;
 776
 777       for (;;)
 778         {
 779           y->avl_balance = x->avl_balance;
 780           if (copy == NULL)
 781             y->avl_data = x->avl_data;
 782           else
 783             {
 784               y->avl_data = copy (x->avl_data, org->avl_param);
 785               if (y->avl_data == NULL)
 786                 {
 787                   y->avl_link[1] = NULL;
 788                   copy_error_recovery (stack, height, new, destroy);
 789                   return NULL;
 790                 }
 791             }
 792
 793           if (x->avl_link[1] != NULL)
 794             {
 795               y->avl_link[1] =
 796                 new->avl_alloc->libavl_malloc (new->avl_alloc,
 797                                                sizeof *y->avl_link[1]);
 798               if (y->avl_link[1] == NULL)
 799                 {
 800                   copy_error_recovery (stack, height, new, destroy);
 801                   return NULL;
 802                 }
 803
 804               x = x->avl_link[1];
 805               y = y->avl_link[1];
 806               break;
 807             }
 808           else
 809             y->avl_link[1] = NULL;
 810
 811           if (height <= 2)
 812             return new;
 813
 814           y = stack[--height];
 815           x = stack[--height];
 816         }
 817     }
 818 }
 819
 820 /* Frees storage allocated for |tree|.
 821    If |destroy != NULL|, applies it to each data item in inorder. */
 822 void
 823 avl_destroy (struct avl_table *tree, avl_item_func *destroy)
 824 {
 825   struct avl_node *p, *q;
 826
 827   assert (tree != NULL);
 828
 829   for (p = tree->avl_root; p != NULL; p = q)
 830     if (p->avl_link[0] == NULL)
 831       {
 832         q = p->avl_link[1];
 833         if (destroy != NULL && p->avl_data != NULL)
 834           destroy (p->avl_data, tree->avl_param);
 835         tree->avl_alloc->libavl_free (tree->avl_alloc, p);
 836       }
 837     else
 838       {
 839         q = p->avl_link[0];
 840         p->avl_link[0] = q->avl_link[1];
 841         q->avl_link[1] = p;
 842       }
 843
 844   tree->avl_alloc->libavl_free (tree->avl_alloc, tree);
 845 }
 846
 847 /* Allocates |size| bytes of space using |malloc()|.
 848    Returns a null pointer if allocation fails. */
 849 void *
 850 avl_malloc (struct libavl_allocator *allocator, size_t size)
 851 {
 852   assert (allocator != NULL && size > 0);
 853   return malloc (size);
 854 }
 855
 856 /* Frees |block|. */
 857 void
 858 avl_free (struct libavl_allocator *allocator, void *block)
 859 {
 860   assert (allocator != NULL && block != NULL);
 861   free (block);
 862 }
 863
 864 /* Default memory allocator that uses |malloc()| and |free()|. */
 865 struct libavl_allocator avl_allocator_default =
 866   {
 867     avl_malloc,
 868     avl_free
 869   };
 870
 871 #undef NDEBUG
 872 #include <assert.h>
 873
 874 /* Asserts that |avl_insert()| succeeds at inserting |item| into |table|. */
 875 void
 876 (avl_assert_insert) (struct avl_table *table, void *item)
 877 {
 878   void **p = avl_probe (table, item);
 879   assert (p != NULL && *p == item);
 880 }
 881
 882 /* Asserts that |avl_delete()| really removes |item| from |table|,
 883    and returns the removed item. */
 884 void *
 885 (avl_assert_delete) (struct avl_table *table, void *item)
 886 {
 887   void *p = avl_delete (table, item);
 888   assert (p != NULL);
 889   return p;
 890 }
 891