external/ibm-public/postfix/dist/src/util/ring.h

   1 /*      $NetBSD$        */
   2
   3 #ifndef _RING_H_INCLUDED_
   4 #define _RING_H_INCLUDED_
   5
   6 /*++
   7 /* NAME
   8 /*      ring 3h
   9 /* SUMMARY
  10 /*      circular list management
  11 /* SYNOPSIS
  12 /*      #include <ring.h>
  13 /* DESCRIPTION
  14 /* .nf
  15
  16  /*
  17   * External interface.
  18   */
  19 typedef struct RING RING;
  20
  21 struct RING {
  22     RING   *succ;                       /* successor */
  23     RING   *pred;                       /* predecessor */
  24 };
  25
  26 extern void ring_init(RING *);
  27 extern void ring_prepend(RING *, RING *);
  28 extern void ring_append(RING *, RING *);
  29 extern void ring_detach(RING *);
  30
  31 #define ring_succ(c) ((c)->succ)
  32 #define ring_pred(c) ((c)->pred)
  33
  34 #define RING_FOREACH(entry, head) \
  35     for (entry = ring_succ(head); entry != (head); entry = ring_succ(entry))
  36
  37  /*
  38   * Typically, an application will embed a RING structure into a larger
  39   * structure that also contains application-specific members. This approach
  40   * gives us the best of both worlds. The application can still use the
  41   * generic RING primitives for manipulating RING structures. The macro below
  42   * transforms a pointer from RING structure to the structure that contains
  43   * it.
  44   */
  45 #define RING_TO_APPL(ring_ptr,app_type,ring_member) \
  46     ((app_type *) (((char *) (ring_ptr)) - offsetof(app_type,ring_member)))
  47
  48 /* LICENSE
  49 /* .ad
  50 /* .fi
  51 /*      The Secure Mailer license must be distributed with this software.
  52 /* AUTHOR(S)
  53 /*      Wietse Venema
  54 /*      IBM T.J. Watson Research
  55 /*      P.O. Box 704
  56 /*      Yorktown Heights, NY 10598, USA
  57 /* LAST MODIFICATION
  58 /*      Tue Jan 28 16:50:20 EST 1997
  59 /*--*/
  60
  61 #endif