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-rw-r--r--src/util/ring.c121
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+/*++
+/* NAME
+/* ring 3
+/* SUMMARY
+/* circular list management
+/* SYNOPSIS
+/* #include <ring.h>
+/*
+/* void ring_init(list)
+/* RING *list;
+/*
+/* void ring_prepend(list, element)
+/* RING *list;
+/* RING *element;
+/*
+/* void ring_append(list, element)
+/* RING *list;
+/* RING *element;
+/*
+/* RING *ring_pred(element)
+/* RING *element;
+/*
+/* RING *ring_succ(element)
+/* RING *element;
+/*
+/* void ring_detach(element)
+/* RING *element;
+/*
+/* RING_FOREACH(RING *element, RING *head)
+/* DESCRIPTION
+/* This module manages circular, doubly-linked, lists. It provides
+/* operations to initialize a list, to add or remove an element,
+/* and to iterate over a list. Although the documentation appears
+/* to emphasize the special role of the list head, each operation
+/* can be applied to each list member.
+/*
+/* Examples of applications: any sequence of objects such as queue,
+/* unordered list, or stack. Typically, an application embeds a RING
+/* structure into its own data structure, and uses the RING primitives
+/* to maintain the linkage between application-specific data objects.
+/*
+/* ring_init() initializes its argument to a list of just one element.
+/*
+/* ring_append() appends the named element to the named list head.
+/*
+/* ring_prepend() prepends the named element to the named list head.
+/*
+/* ring_succ() returns the list element that follows its argument.
+/*
+/* ring_pred() returns the list element that precedes its argument.
+/*
+/* ring_detach() disconnects a list element from its neighbors
+/* and closes the hole. This routine performs no implicit ring_init()
+/* on the removed element.
+/*
+/* RING_FOREACH() is a macro that expands to a for (... ; ... ; ...)
+/* statement that iterates over each list element in forward order.
+/* Upon completion, the \fIelement\fR variable is set equal to
+/* \fIhead\fR. The list head itself is not treated as a list member.
+/* LICENSE
+/* .ad
+/* .fi
+/* The Secure Mailer license must be distributed with this software.
+/* AUTHOR(S)
+/* Wietse Venema
+/* IBM T.J. Watson Research
+/* P.O. Box 704
+/* Yorktown Heights, NY 10598, USA
+/*--*/
+
+/* System libraries. */
+
+/* Application-specific. */
+
+#include "ring.h"
+
+/* ring_init - initialize ring head */
+
+void ring_init(ring)
+RING *ring;
+{
+ ring->pred = ring->succ = ring;
+}
+
+/* ring_append - insert entry after ring head */
+
+void ring_append(ring, entry)
+RING *ring;
+RING *entry;
+{
+ entry->succ = ring->succ;
+ entry->pred = ring;
+ ring->succ->pred = entry;
+ ring->succ = entry;
+}
+
+/* ring_prepend - insert new entry before ring head */
+
+void ring_prepend(ring, entry)
+RING *ring;
+RING *entry;
+{
+ entry->pred = ring->pred;
+ entry->succ = ring;
+ ring->pred->succ = entry;
+ ring->pred = entry;
+}
+
+/* ring_detach - remove entry from ring */
+
+void ring_detach(entry)
+RING *entry;
+{
+ RING *succ = entry->succ;
+ RING *pred = entry->pred;
+
+ pred->succ = succ;
+ succ->pred = pred;
+
+ entry->succ = entry->pred = 0;
+}