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+/*
+ * ANSI C Library for maintainance of AVL Balanced Trees
+ *
+ * ref.:
+ *  G. M. Adelson-Velskij & E. M. Landis
+ *  Doklady Akad. Nauk SSSR 146 (1962), 263-266
+ *
+ * see also:
+ *  D. E. Knuth: The Art of Computer Programming Vol.3 (Sorting and Searching)
+ *
+ * (C) 2000 Daniel Nagy, Budapest University of Technology and Economics
+ * Released under GNU General Public License (GPL) version 2
+ *
+ */
+#ifndef _AVL_H
+#define _AVL_H 1
+
+#include <pthread.h>
+
+// #define AVL_LOCK_WITH_MUTEX 1
+
+/* Data structures */
+
+/* One element of the AVL tree */
+typedef struct avl {
+	struct avl* left;
+	struct avl* right;
+	signed char balance;
+} avl;
+
+/* An AVL tree */
+typedef struct avl_tree {
+	avl* root;
+	int (*compar)(void* a, void* b);
+
+#ifdef AVL_LOCK_WITH_MUTEX
+	pthread_mutex_t mutex;
+#else
+	pthread_rwlock_t rwlock;
+#endif
+} avl_tree;
+
+/* Public methods */
+
+/* Insert element a into the AVL tree t
+ * returns 1 if the depth of the tree has grown
+ * Warning: do not insert elements already present
+ */
+int avl_insert(avl_tree* t, avl* a);
+
+/* Remove an element a from the AVL tree t
+ * returns -1 if the depth of the tree has shrunk
+ * Warning: if the element is not present in the tree,
+ *          returns 0 as if it had been removed succesfully.
+ */
+int avl_remove(avl_tree* t, avl* a);
+
+/* Remove the root of the AVL tree t
+ * Warning: dumps core if t is empty
+ */
+int avl_removeroot(avl_tree* t);
+
+/* Iterate through elements in t from a range between a and b (inclusive)
+ * for each element calls iter(a) until it returns 0
+ * returns the last value returned by iterator or 0 if there were no calls
+ * Warning: a<=b must hold
+ */
+int avl_range(avl_tree* t, avl* a, avl* b, int (*iter)(avl*), avl** ret);
+
+/* Iterate through elements in t equal to a
+ * for each element calls iter(a) until it returns 0
+ * returns the last value returned by iterator or 0 if there were no calls
+ */
+int avl_search(avl_tree* t, avl* a, int (*iter)(avl*), avl** ret);
+
+/* Initialize the avl_tree
+ */
+void avl_init(avl_tree* t, int (*compar)(void* a, void* b));
+
+#endif /* avl.h */