git.sur5r.net Git - openldap/blob - include/ldap_queue.h

   1 /*
   2  * Copyright 2001-2002 The OpenLDAP Foundation, Redwood City, California, USA
   3  * All rights reserved.
   4  *
   5  * Redistribution and use in source and binary forms, with or without
   6  * modification, are permitted only as authorized by the OpenLDAP
   7  * Public License.  A copy of this license is available at
   8  * http://www.OpenLDAP.org/license.html or in file LICENSE in the
   9  * top-level directory of the distribution.
  10  */
  11 /* stolen from FreeBSD for use in OpenLDAP */
  12 /* $OpenLDAP$ */
  13 /*
  14  * Copyright (c) 1991, 1993
  15  *      The Regents of the University of California.  All rights reserved.
  16  *
  17  * Redistribution and use in source and binary forms, with or without
  18  * modification, are permitted provided that the following conditions
  19  * are met:
  20  * 1. Redistributions of source code must retain the above copyright
  21  *    notice, this list of conditions and the following disclaimer.
  22  * 2. Redistributions in binary form must reproduce the above copyright
  23  *    notice, this list of conditions and the following disclaimer in the
  24  *    documentation and/or other materials provided with the distribution.
  25  * 3. All advertising materials mentioning features or use of this software
  26  *    must display the following acknowledgement:
  27  *      This product includes software developed by the University of
  28  *      California, Berkeley and its contributors.
  29  * 4. Neither the name of the University nor the names of its contributors
  30  *    may be used to endorse or promote products derived from this software
  31  *    without specific prior written permission.
  32  *
  33  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  34  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  35  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  36  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  37  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  38  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  39  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  40  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  41  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  42  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  43  * SUCH DAMAGE.
  44  *
  45  *      @(#)queue.h     8.5 (Berkeley) 8/20/94
  46  * $FreeBSD: src/sys/sys/queue.h,v 1.32.2.5 2001/09/30 21:12:54 luigi Exp $
  47  */
  48
  49 #ifndef _LDAP_QUEUE_H_
  50 #define _LDAP_QUEUE_H_
  51
  52 /*
  53  * This file defines five types of data structures: singly-linked lists,
  54  * singly-linked tail queues, lists, tail queues, and circular queues.
  55  *
  56  * A singly-linked list is headed by a single forward pointer. The elements
  57  * are singly linked for minimum space and pointer manipulation overhead at
  58  * the expense of O(n) removal for arbitrary elements. New elements can be
  59  * added to the list after an existing element or at the head of the list.
  60  * Elements being removed from the head of the list should use the explicit
  61  * macro for this purpose for optimum efficiency. A singly-linked list may
  62  * only be traversed in the forward direction.  Singly-linked lists are ideal
  63  * for applications with large datasets and few or no removals or for
  64  * implementing a LIFO queue.
  65  *
  66  * A singly-linked tail queue is headed by a pair of pointers, one to the
  67  * head of the list and the other to the tail of the list. The elements are
  68  * singly linked for minimum space and pointer manipulation overhead at the
  69  * expense of O(n) removal for arbitrary elements. New elements can be added
  70  * to the list after an existing element, at the head of the list, or at the
  71  * end of the list. Elements being removed from the head of the tail queue
  72  * should use the explicit macro for this purpose for optimum efficiency.
  73  * A singly-linked tail queue may only be traversed in the forward direction.
  74  * Singly-linked tail queues are ideal for applications with large datasets
  75  * and few or no removals or for implementing a FIFO queue.
  76  *
  77  * A list is headed by a single forward pointer (or an array of forward
  78  * pointers for a hash table header). The elements are doubly linked
  79  * so that an arbitrary element can be removed without a need to
  80  * traverse the list. New elements can be added to the list before
  81  * or after an existing element or at the head of the list. A list
  82  * may only be traversed in the forward direction.
  83  *
  84  * A tail queue is headed by a pair of pointers, one to the head of the
  85  * list and the other to the tail of the list. The elements are doubly
  86  * linked so that an arbitrary element can be removed without a need to
  87  * traverse the list. New elements can be added to the list before or
  88  * after an existing element, at the head of the list, or at the end of
  89  * the list. A tail queue may be traversed in either direction.
  90  *
  91  * A circle queue is headed by a pair of pointers, one to the head of the
  92  * list and the other to the tail of the list. The elements are doubly
  93  * linked so that an arbitrary element can be removed without a need to
  94  * traverse the list. New elements can be added to the list before or after
  95  * an existing element, at the head of the list, or at the end of the list.
  96  * A circle queue may be traversed in either direction, but has a more
  97  * complex end of list detection.
  98  *
  99  * For details on the use of these macros, see the queue(3) manual page.
 100  * All macros are prefixed with LDAP_.
 101  *
 102  *                      SLIST_  LIST_   STAILQ_ TAILQ_  CIRCLEQ_
 103  * _HEAD                +       +       +       +       +
 104  * _ENTRY               +       +       +       +       +
 105  * _INIT                +       +       +       +       +
 106  * _EMPTY               +       +       +       +       +
 107  * _FIRST               +       +       +       +       +
 108  * _NEXT                +       +       +       +       +
 109  * _PREV                -       -       -       +       +
 110  * _LAST                -       -       +       +       +
 111  * _FOREACH             +       +       +       +       +
 112  * _FOREACH_REVERSE     -       -       -       +       +
 113  * _INSERT_HEAD         +       +       +       +       +
 114  * _INSERT_BEFORE       -       +       -       +       +
 115  * _INSERT_AFTER        +       +       +       +       +
 116  * _INSERT_TAIL         -       -       +       +       +
 117  * _REMOVE_HEAD         +       -       +       -       -
 118  * _REMOVE              +       +       +       +       +
 119  *
 120  */
 121
 122 /*
 123  * Singly-linked List definitions.
 124  */
 125 #define LDAP_SLIST_HEAD(name, type)                                     \
 126 struct name {                                                           \
 127         struct type *slh_first; /* first element */                     \
 128 }
 129
 130 #define LDAP_SLIST_HEAD_INITIALIZER(head)                               \
 131         { NULL }
 132
 133 #define LDAP_SLIST_ENTRY(type)                                          \
 134 struct {                                                                \
 135         struct type *sle_next;  /* next element */                      \
 136 }
 137
 138 /*
 139  * Singly-linked List functions.
 140  */
 141 #define LDAP_SLIST_EMPTY(head)  ((head)->slh_first == NULL)
 142
 143 #define LDAP_SLIST_FIRST(head)  ((head)->slh_first)
 144
 145 #define LDAP_SLIST_FOREACH(var, head, field)                            \
 146         for((var) = (head)->slh_first; (var); (var) = (var)->field.sle_next)
 147
 148 #define LDAP_SLIST_INIT(head) {                                         \
 149         (head)->slh_first = NULL;                                       \
 150 }
 151
 152 #define LDAP_SLIST_INSERT_AFTER(slistelm, elm, field) do {              \
 153         (elm)->field.sle_next = (slistelm)->field.sle_next;             \
 154         (slistelm)->field.sle_next = (elm);                             \
 155 } while (0)
 156
 157 #define LDAP_SLIST_INSERT_HEAD(head, elm, field) do {                   \
 158         (elm)->field.sle_next = (head)->slh_first;                      \
 159         (head)->slh_first = (elm);                                      \
 160 } while (0)
 161
 162 #define LDAP_SLIST_NEXT(elm, field)     ((elm)->field.sle_next)
 163
 164 #define LDAP_SLIST_REMOVE_HEAD(head, field) do {                        \
 165         (head)->slh_first = (head)->slh_first->field.sle_next;          \
 166 } while (0)
 167
 168 #define LDAP_SLIST_REMOVE(head, elm, type, field) do {                  \
 169         if ((head)->slh_first == (elm)) {                               \
 170                 LDAP_SLIST_REMOVE_HEAD((head), field);                  \
 171         }                                                               \
 172         else {                                                          \
 173                 struct type *curelm = (head)->slh_first;                \
 174                 while( curelm->field.sle_next != (elm) )                \
 175                         curelm = curelm->field.sle_next;                \
 176                 curelm->field.sle_next =                                \
 177                     curelm->field.sle_next->field.sle_next;             \
 178         }                                                               \
 179 } while (0)
 180
 181 /*
 182  * Singly-linked Tail queue definitions.
 183  */
 184 #define LDAP_STAILQ_HEAD(name, type)                                    \
 185 struct name {                                                           \
 186         struct type *stqh_first;/* first element */                     \
 187         struct type **stqh_last;/* addr of last next element */         \
 188 }
 189
 190 #define LDAP_STAILQ_HEAD_INITIALIZER(head)                              \
 191         { NULL, &(head).stqh_first }
 192
 193 #define LDAP_STAILQ_ENTRY(type)                                         \
 194 struct {                                                                \
 195         struct type *stqe_next; /* next element */                      \
 196 }
 197
 198 /*
 199  * Singly-linked Tail queue functions.
 200  */
 201 #define LDAP_STAILQ_EMPTY(head) ((head)->stqh_first == NULL)
 202
 203 #define LDAP_STAILQ_INIT(head) do {                                     \
 204         (head)->stqh_first = NULL;                                      \
 205         (head)->stqh_last = &(head)->stqh_first;                        \
 206 } while (0)
 207
 208 #define LDAP_STAILQ_FIRST(head) ((head)->stqh_first)
 209
 210 #define LDAP_STAILQ_LAST(head, type, field)                             \
 211         (LDAP_STAILQ_EMPTY(head) ?                                      \
 212                 NULL :                                                  \
 213                 ((struct type *)                                        \
 214                 ((char *)((head)->stqh_last) - offsetof(struct type, field))))
 215
 216 #define LDAP_STAILQ_FOREACH(var, head, field)                           \
 217         for((var) = (head)->stqh_first; (var); (var) = (var)->field.stqe_next)
 218
 219 #define LDAP_STAILQ_INSERT_HEAD(head, elm, field) do {                  \
 220         if (((elm)->field.stqe_next = (head)->stqh_first) == NULL)      \
 221                 (head)->stqh_last = &(elm)->field.stqe_next;            \
 222         (head)->stqh_first = (elm);                                     \
 223 } while (0)
 224
 225 #define LDAP_STAILQ_INSERT_TAIL(head, elm, field) do {                  \
 226         (elm)->field.stqe_next = NULL;                                  \
 227         *(head)->stqh_last = (elm);                                     \
 228         (head)->stqh_last = &(elm)->field.stqe_next;                    \
 229 } while (0)
 230
 231 #define LDAP_STAILQ_INSERT_AFTER(head, tqelm, elm, field) do {          \
 232         if (((elm)->field.stqe_next = (tqelm)->field.stqe_next) == NULL)\
 233                 (head)->stqh_last = &(elm)->field.stqe_next;            \
 234         (tqelm)->field.stqe_next = (elm);                               \
 235 } while (0)
 236
 237 #define LDAP_STAILQ_NEXT(elm, field)    ((elm)->field.stqe_next)
 238
 239 #define LDAP_STAILQ_REMOVE_HEAD(head, field) do {                       \
 240         if (((head)->stqh_first =                                       \
 241              (head)->stqh_first->field.stqe_next) == NULL)              \
 242                 (head)->stqh_last = &(head)->stqh_first;                \
 243 } while (0)
 244
 245 #define LDAP_STAILQ_REMOVE_HEAD_UNTIL(head, elm, field) do {            \
 246         if (((head)->stqh_first = (elm)->field.stqe_next) == NULL)      \
 247                 (head)->stqh_last = &(head)->stqh_first;                \
 248 } while (0)
 249
 250 #define LDAP_STAILQ_REMOVE(head, elm, type, field) do {                 \
 251         if ((head)->stqh_first == (elm)) {                              \
 252                 LDAP_STAILQ_REMOVE_HEAD(head, field);                   \
 253         }                                                               \
 254         else {                                                          \
 255                 struct type *curelm = (head)->stqh_first;               \
 256                 while( curelm->field.stqe_next != (elm) )               \
 257                         curelm = curelm->field.stqe_next;               \
 258                 if((curelm->field.stqe_next =                           \
 259                     curelm->field.stqe_next->field.stqe_next) == NULL)  \
 260                         (head)->stqh_last = &(curelm)->field.stqe_next; \
 261         }                                                               \
 262 } while (0)
 263
 264 /*
 265  * List definitions.
 266  */
 267 #define LDAP_LIST_HEAD(name, type)                                      \
 268 struct name {                                                           \
 269         struct type *lh_first;  /* first element */                     \
 270 }
 271
 272 #define LDAP_LIST_HEAD_INITIALIZER(head)                                \
 273         { NULL }
 274
 275 #define LDAP_LIST_ENTRY(type)                                           \
 276 struct {                                                                \
 277         struct type *le_next;   /* next element */                      \
 278         struct type **le_prev;  /* address of previous next element */  \
 279 }
 280
 281 /*
 282  * List functions.
 283  */
 284
 285 #define LDAP_LIST_EMPTY(head) ((head)->lh_first == NULL)
 286
 287 #define LDAP_LIST_FIRST(head)   ((head)->lh_first)
 288
 289 #define LDAP_LIST_FOREACH(var, head, field)                             \
 290         for((var) = (head)->lh_first; (var); (var) = (var)->field.le_next)
 291
 292 #define LDAP_LIST_INIT(head) do {                                       \
 293         (head)->lh_first = NULL;                                        \
 294 } while (0)
 295
 296 #define LDAP_LIST_INSERT_AFTER(listelm, elm, field) do {                \
 297         if (((elm)->field.le_next = (listelm)->field.le_next) != NULL)  \
 298                 (listelm)->field.le_next->field.le_prev =               \
 299                     &(elm)->field.le_next;                              \
 300         (listelm)->field.le_next = (elm);                               \
 301         (elm)->field.le_prev = &(listelm)->field.le_next;               \
 302 } while (0)
 303
 304 #define LDAP_LIST_INSERT_BEFORE(listelm, elm, field) do {               \
 305         (elm)->field.le_prev = (listelm)->field.le_prev;                \
 306         (elm)->field.le_next = (listelm);                               \
 307         *(listelm)->field.le_prev = (elm);                              \
 308         (listelm)->field.le_prev = &(elm)->field.le_next;               \
 309 } while (0)
 310
 311 #define LDAP_LIST_INSERT_HEAD(head, elm, field) do {                    \
 312         if (((elm)->field.le_next = (head)->lh_first) != NULL)          \
 313                 (head)->lh_first->field.le_prev = &(elm)->field.le_next;\
 314         (head)->lh_first = (elm);                                       \
 315         (elm)->field.le_prev = &(head)->lh_first;                       \
 316 } while (0)
 317
 318 #define LDAP_LIST_NEXT(elm, field)      ((elm)->field.le_next)
 319
 320 #define LDAP_LIST_REMOVE(elm, field) do {                               \
 321         if ((elm)->field.le_next != NULL)                               \
 322                 (elm)->field.le_next->field.le_prev =                   \
 323                     (elm)->field.le_prev;                               \
 324         *(elm)->field.le_prev = (elm)->field.le_next;                   \
 325 } while (0)
 326
 327 /*
 328  * Tail queue definitions.
 329  */
 330 #define LDAP_TAILQ_HEAD(name, type)                                     \
 331 struct name {                                                           \
 332         struct type *tqh_first; /* first element */                     \
 333         struct type **tqh_last; /* addr of last next element */         \
 334 }
 335
 336 #define LDAP_TAILQ_HEAD_INITIALIZER(head)                               \
 337         { NULL, &(head).tqh_first }
 338
 339 #define LDAP_TAILQ_ENTRY(type)                                          \
 340 struct {                                                                \
 341         struct type *tqe_next;  /* next element */                      \
 342         struct type **tqe_prev; /* address of previous next element */  \
 343 }
 344
 345 /*
 346  * Tail queue functions.
 347  */
 348 #define LDAP_TAILQ_EMPTY(head) ((head)->tqh_first == NULL)
 349
 350 #define LDAP_TAILQ_FOREACH(var, head, field)                            \
 351         for (var = LDAP_TAILQ_FIRST(head); var; var = TAILQ_NEXT(var, field))
 352
 353 #define LDAP_TAILQ_FOREACH_REVERSE(var, head, headname, field)          \
 354         for ((var) = LDAP_TAILQ_LAST((head), headname);                 \
 355              (var);                                                     \
 356              (var) = LDAP_TAILQ_PREV((var), headname, field))
 357
 358 #define LDAP_TAILQ_FIRST(head) ((head)->tqh_first)
 359
 360 #define LDAP_TAILQ_LAST(head, headname) \
 361         (*(((struct headname *)((head)->tqh_last))->tqh_last))
 362
 363 #define LDAP_TAILQ_NEXT(elm, field) ((elm)->field.tqe_next)
 364
 365 #define LDAP_TAILQ_PREV(elm, headname, field) \
 366         (*(((struct headname *)((elm)->field.tqe_prev))->tqh_last))
 367
 368 #define LDAP_TAILQ_INIT(head) do {                                      \
 369         (head)->tqh_first = NULL;                                       \
 370         (head)->tqh_last = &(head)->tqh_first;                          \
 371 } while (0)
 372
 373 #define LDAP_TAILQ_INSERT_HEAD(head, elm, field) do {                   \
 374         if (((elm)->field.tqe_next = (head)->tqh_first) != NULL)        \
 375                 (head)->tqh_first->field.tqe_prev =                     \
 376                     &(elm)->field.tqe_next;                             \
 377         else                                                            \
 378                 (head)->tqh_last = &(elm)->field.tqe_next;              \
 379         (head)->tqh_first = (elm);                                      \
 380         (elm)->field.tqe_prev = &(head)->tqh_first;                     \
 381 } while (0)
 382
 383 #define LDAP_TAILQ_INSERT_TAIL(head, elm, field) do {                   \
 384         (elm)->field.tqe_next = NULL;                                   \
 385         (elm)->field.tqe_prev = (head)->tqh_last;                       \
 386         *(head)->tqh_last = (elm);                                      \
 387         (head)->tqh_last = &(elm)->field.tqe_next;                      \
 388 } while (0)
 389
 390 #define LDAP_TAILQ_INSERT_AFTER(head, listelm, elm, field) do {         \
 391         if (((elm)->field.tqe_next = (listelm)->field.tqe_next) != NULL)\
 392                 (elm)->field.tqe_next->field.tqe_prev =                 \
 393                     &(elm)->field.tqe_next;                             \
 394         else                                                            \
 395                 (head)->tqh_last = &(elm)->field.tqe_next;              \
 396         (listelm)->field.tqe_next = (elm);                              \
 397         (elm)->field.tqe_prev = &(listelm)->field.tqe_next;             \
 398 } while (0)
 399
 400 #define LDAP_TAILQ_INSERT_BEFORE(listelm, elm, field) do {              \
 401         (elm)->field.tqe_prev = (listelm)->field.tqe_prev;              \
 402         (elm)->field.tqe_next = (listelm);                              \
 403         *(listelm)->field.tqe_prev = (elm);                             \
 404         (listelm)->field.tqe_prev = &(elm)->field.tqe_next;             \
 405 } while (0)
 406
 407 #define LDAP_TAILQ_REMOVE(head, elm, field) do {                        \
 408         if (((elm)->field.tqe_next) != NULL)                            \
 409                 (elm)->field.tqe_next->field.tqe_prev =                 \
 410                     (elm)->field.tqe_prev;                              \
 411         else                                                            \
 412                 (head)->tqh_last = (elm)->field.tqe_prev;               \
 413         *(elm)->field.tqe_prev = (elm)->field.tqe_next;                 \
 414 } while (0)
 415
 416 /*
 417  * Circular queue definitions.
 418  */
 419 #define LDAP_CIRCLEQ_HEAD(name, type)                                   \
 420 struct name {                                                           \
 421         struct type *cqh_first;         /* first element */             \
 422         struct type *cqh_last;          /* last element */              \
 423 }
 424
 425 #define LDAP_CIRCLEQ_ENTRY(type)                                        \
 426 struct {                                                                \
 427         struct type *cqe_next;          /* next element */              \
 428         struct type *cqe_prev;          /* previous element */          \
 429 }
 430
 431 /*
 432  * Circular queue functions.
 433  */
 434 #define LDAP_CIRCLEQ_EMPTY(head) ((head)->cqh_first == (void *)(head))
 435
 436 #define LDAP_CIRCLEQ_FIRST(head) ((head)->cqh_first)
 437
 438 #define LDAP_CIRCLEQ_FOREACH(var, head, field)                          \
 439         for((var) = (head)->cqh_first;                                  \
 440             (var) != (void *)(head);                                    \
 441             (var) = (var)->field.cqe_next)
 442
 443 #define LDAP_CIRCLEQ_FOREACH_REVERSE(var, head, field)                  \
 444         for((var) = (head)->cqh_last;                                   \
 445             (var) != (void *)(head);                                    \
 446             (var) = (var)->field.cqe_prev)
 447
 448 #define LDAP_CIRCLEQ_INIT(head) do {                                    \
 449         (head)->cqh_first = (void *)(head);                             \
 450         (head)->cqh_last = (void *)(head);                              \
 451 } while (0)
 452
 453 #define LDAP_CIRCLEQ_INSERT_AFTER(head, listelm, elm, field) do {       \
 454         (elm)->field.cqe_next = (listelm)->field.cqe_next;              \
 455         (elm)->field.cqe_prev = (listelm);                              \
 456         if ((listelm)->field.cqe_next == (void *)(head))                \
 457                 (head)->cqh_last = (elm);                               \
 458         else                                                            \
 459                 (listelm)->field.cqe_next->field.cqe_prev = (elm);      \
 460         (listelm)->field.cqe_next = (elm);                              \
 461 } while (0)
 462
 463 #define LDAP_CIRCLEQ_INSERT_BEFORE(head, listelm, elm, field) do {      \
 464         (elm)->field.cqe_next = (listelm);                              \
 465         (elm)->field.cqe_prev = (listelm)->field.cqe_prev;              \
 466         if ((listelm)->field.cqe_prev == (void *)(head))                \
 467                 (head)->cqh_first = (elm);                              \
 468         else                                                            \
 469                 (listelm)->field.cqe_prev->field.cqe_next = (elm);      \
 470         (listelm)->field.cqe_prev = (elm);                              \
 471 } while (0)
 472
 473 #define LDAP_CIRCLEQ_INSERT_HEAD(head, elm, field) do {                 \
 474         (elm)->field.cqe_next = (head)->cqh_first;                      \
 475         (elm)->field.cqe_prev = (void *)(head);                         \
 476         if ((head)->cqh_last == (void *)(head))                         \
 477                 (head)->cqh_last = (elm);                               \
 478         else                                                            \
 479                 (head)->cqh_first->field.cqe_prev = (elm);              \
 480         (head)->cqh_first = (elm);                                      \
 481 } while (0)
 482
 483 #define LDAP_CIRCLEQ_INSERT_TAIL(head, elm, field) do {                 \
 484         (elm)->field.cqe_next = (void *)(head);                         \
 485         (elm)->field.cqe_prev = (head)->cqh_last;                       \
 486         if ((head)->cqh_first == (void *)(head))                        \
 487                 (head)->cqh_first = (elm);                              \
 488         else                                                            \
 489                 (head)->cqh_last->field.cqe_next = (elm);               \
 490         (head)->cqh_last = (elm);                                       \
 491 } while (0)
 492
 493 #define LDAP_CIRCLEQ_LAST(head) ((head)->cqh_last)
 494
 495 #define LDAP_CIRCLEQ_NEXT(elm,field) ((elm)->field.cqe_next)
 496
 497 #define LDAP_CIRCLEQ_PREV(elm,field) ((elm)->field.cqe_prev)
 498
 499 #define LDAP_CIRCLEQ_REMOVE(head, elm, field) do {                      \
 500         if ((elm)->field.cqe_next == (void *)(head))                    \
 501                 (head)->cqh_last = (elm)->field.cqe_prev;               \
 502         else                                                            \
 503                 (elm)->field.cqe_next->field.cqe_prev =                 \
 504                     (elm)->field.cqe_prev;                              \
 505         if ((elm)->field.cqe_prev == (void *)(head))                    \
 506                 (head)->cqh_first = (elm)->field.cqe_next;              \
 507         else                                                            \
 508                 (elm)->field.cqe_prev->field.cqe_next =                 \
 509                     (elm)->field.cqe_next;                              \
 510 } while (0)
 511
 512 #endif /* !_LDAP_QUEUE_H_ */