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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;
}
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