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+/* Helper functions for maintaining a fixed-size lru-ordered queue
+
+   Copyright (C) 1996 Free Software Foundation, Inc.
+
+   Written by Miles Bader <miles@gnu.ai.mit.edu>
+
+   This program is free software; you can redistribute it and/or
+   modify it under the terms of the GNU General Public License as
+   published by the Free Software Foundation; either version 2, or (at
+   your option) any later version.
+
+   This program is distributed in the hope that it will be useful, but
+   WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program; if not, write to the Free Software
+   Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. */
+
+#ifndef __CACHEQ_H__
+#define __CACHEQ_H__
+
+#include <stddef.h>
+#include <errno.h>
+
+/* This header occurs at the start of every cacheq entry.  */
+struct cacheq_hdr
+{
+  /* Next and prev entries in the cache, linked in LRU order.  These are of
+     type `void *' so that it's conveient to iterate through the list using a
+     variable pointing to a structure that contains the header, by using
+     something like `VAR = VAR->hdr.next'.  */
+  void *next, *prev;
+};
+
+/* A cacheq.  Note that this structure is laid out to allow convenient use as
+   static initialized data.  */
+struct cacheq
+{
+  /* The size of each entry, including its cacheq_hdr.  */
+  size_t entry_size;
+
+  /* If non-0, then when making new entries (for instance, when the cacheq is
+     initialized, or when its size is increased), this function is called on
+     each new entry (with it's header already initialized).  If this function
+     isn't defined, then each entry is simply zeroed.  */
+  void (*init_entry) (void *entry);
+
+  /* When an entry is moved from one place in memory to another (for
+     instance, changing the size of the cache, new storage is used), this is
+     called for each entry, with FROM and TO the old and new locations of the
+     entry (and TO contains a bitwise copy of FROM).  This is often useful
+     when the entry points to something that contains a backpointer to it.  */
+  void (*move_entry) (void *from, void *to);
+
+  /* When entries are removed for some reason (for instance, when reducing
+     the size of the cacheq), this function is called on each.  */
+  void (*finalize_entry) (void *entry);
+
+  /* The number of entries in the cache.  This number is fixed.  */
+  int length;
+
+  /* A buffer holding malloc'd memory for all the entries -- NUM_ENTRIES
+     entries of size ENTRY_SIZE.  */
+  void *entries;
+
+  /* The least, and most, recently used entries in the cache.  These point to
+     either end of a linked list composed of all the elements of the cache.
+     This list will always be the same length -- if an element is `removed',
+     its entry is simply marked inactive, and moved to the LRU end of the list
+     so it will be reused first.  */
+  struct cacheq_hdr *lru, *mru;
+};
+
+/* Move ENTRY to the most-recently-used end of CACHEQ.  */
+void cacheq_make_mru (struct cacheq *cq, void *entry);
+
+/* Move ENTRY to the least-recently-used end of CACHEQ. */
+void cacheq_make_lru (struct cacheq *cq, void *entry);
+
+/* Change CQ's size to be LENGTH entries.  */
+error_t cacheq_set_length (struct cacheq *cq, int length);
+
+#endif /* __CACHEQ_H__ */