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      1 /*	$NetBSD: ring.h,v 1.1.1.1 2009/06/23 10:09:00 tron Exp $	*/
      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
     62