path: root/src/avl.c

/*
 * 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
 *
 */

#ifdef HAVE_CONFIG_H
#include <config.h>
#endif
#include "avl.h"

/* Private methods */
int _avl_removeroot(avl_tree* t);

/* Swing to the left
 * Warning: no balance maintainance
 */
void avl_swl(avl** root) {
	avl* a = *root;
	avl* b = a->right;
	*root = b;
	a->right = b->left;
	b->left = a;
}

/* Swing to the right
 * Warning: no balance maintainance
 */
void avl_swr(avl** root) {
	avl* a = *root;
	avl* b = a->left;
	*root = b;
	a->left = b->right;
	b->right = a;
}

/* Balance maintainance after especially nasty swings
 */
void avl_nasty(avl* root) {
	switch (root->balance) {
	case -1:
		root->left->balance = 0;
		root->right->balance = 1;
		break;
	case 1:
		root->left->balance = -1;
		root->right->balance = 0;
		break;
	case 0:
		root->left->balance = 0;
		root->right->balance = 0;
	}
	root->balance = 0;
}

/* 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) {
	/* initialize */
	a->left = 0;
	a->right = 0;
	a->balance = 0;
	/* insert into an empty tree */
	if (!t->root) {
		t->root = a;
		return 1;
	}

	if (t->compar(t->root, a) > 0) {
		/* insert into the left subtree */
		if (t->root->left) {
			avl_tree left_subtree;
			left_subtree.root = t->root->left;
			left_subtree.compar = t->compar;
			if (_avl_insert(&left_subtree, a)) {
				switch (t->root->balance--) {
				case 1:
					return 0;
				case 0:
					return 1;
				}
				if (t->root->left->balance < 0) {
					avl_swr(&(t->root));
					t->root->balance = 0;
					t->root->right->balance = 0;
				} else {
					avl_swl(&(t->root->left));
					avl_swr(&(t->root));
					avl_nasty(t->root);
				}
			} else
				t->root->left = left_subtree.root;
			return 0;
		} else {
			t->root->left = a;
			if (t->root->balance--)
				return 0;
			return 1;
		}
	} else {
		/* insert into the right subtree */
		if (t->root->right) {
			avl_tree right_subtree;
			right_subtree.root = t->root->right;
			right_subtree.compar = t->compar;
			if (_avl_insert(&right_subtree, a)) {
				switch (t->root->balance++) {
				case -1:
					return 0;
				case 0:
					return 1;
				}
				if (t->root->right->balance > 0) {
					avl_swl(&(t->root));
					t->root->balance = 0;
					t->root->left->balance = 0;
				} else {
					avl_swr(&(t->root->right));
					avl_swl(&(t->root));
					avl_nasty(t->root);
				}
			} else
				t->root->right = right_subtree.root;
			return 0;
		} else {
			t->root->right = a;
			if (t->root->balance++)
				return 0;
			return 1;
		}
	}
}
int avl_insert(avl_tree* t, avl* a) {
#ifdef AVL_LOCK_WITH_MUTEX
	pthread_mutex_lock(&t->mutex);
#else
	pthread_rwlock_wrlock(&t->rwlock);
#endif

	int ret = _avl_insert(t, a);

#ifdef AVL_LOCK_WITH_MUTEX
	pthread_mutex_unlock(&t->mutex);
#else
	pthread_rwlock_unlock(&t->rwlock);
#endif
	return ret;
}

/* 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) {
	int b;
	if (t->root == a)
		return _avl_removeroot(t);
	b = t->compar(t->root, a);
	if (b >= 0) {
		/* remove from the left subtree */
		int ch;
		avl_tree left_subtree;
		if ((left_subtree.root = t->root->left)) {
			left_subtree.compar = t->compar;
			ch = _avl_remove(&left_subtree, a);
			t->root->left = left_subtree.root;
			if (ch) {
				switch (t->root->balance++) {
				case -1:
					return -1;
				case 0:
					return 0;
				}
				switch (t->root->right->balance) {
				case 0:
					avl_swl(&(t->root));
					t->root->balance = -1;
					t->root->left->balance = 1;
					return 0;
				case 1:
					avl_swl(&(t->root));
					t->root->balance = 0;
					t->root->left->balance = 0;
					return -1;
				}
				avl_swr(&(t->root->right));
				avl_swl(&(t->root));
				avl_nasty(t->root);
				return -1;
			}
		}
	}
	if (b <= 0) {
		/* remove from the right subtree */
		int ch;
		avl_tree right_subtree;
		if ((right_subtree.root = t->root->right)) {
			right_subtree.compar = t->compar;
			ch = _avl_remove(&right_subtree, a);
			t->root->right = right_subtree.root;
			if (ch) {
				switch (t->root->balance--) {
				case 1:
					return -1;
				case 0:
					return 0;
				}
				switch (t->root->left->balance) {
				case 0:
					avl_swr(&(t->root));
					t->root->balance = 1;
					t->root->right->balance = -1;
					return 0;
				case -1:
					avl_swr(&(t->root));
					t->root->balance = 0;
					t->root->right->balance = 0;
					return -1;
				}
				avl_swl(&(t->root->left));
				avl_swr(&(t->root));
				avl_nasty(t->root);
				return -1;
			}
		}
	}
	return 0;
}

int avl_remove(avl_tree* t, avl* a) {
#ifdef AVL_LOCK_WITH_MUTEX
	pthread_mutex_lock(&t->mutex);
#else
	pthread_rwlock_wrlock(&t->rwlock);
#endif

	int ret = _avl_remove(t, a);

#ifdef AVL_LOCK_WITH_MUTEX
	pthread_mutex_unlock(&t->mutex);
#else
	pthread_rwlock_unlock(&t->rwlock);
#endif
	return ret;
}

/* Remove the root of the AVL tree t
 * Warning: dumps core if t is empty
 */
int _avl_removeroot(avl_tree* t) {
	int ch;
	avl* a;
	if (!t->root->left) {
		if (!t->root->right) {
			t->root = 0;
			return -1;
		}
		t->root = t->root->right;
		return -1;
	}
	if (!t->root->right) {
		t->root = t->root->left;
		return -1;
	}
	if (t->root->balance < 0) {
		/* remove from the left subtree */
		a = t->root->left;
		while (a->right)
			a = a->right;
	} else {
		/* remove from the right subtree */
		a = t->root->right;
		while (a->left)
			a = a->left;
	}
	ch = _avl_remove(t, a);
	a->left = t->root->left;
	a->right = t->root->right;
	a->balance = t->root->balance;
	t->root = a;
	if (a->balance == 0)
		return ch;
	return 0;
}

int avl_removeroot(avl_tree* t) {
#ifdef AVL_LOCK_WITH_MUTEX
	pthread_mutex_lock(&t->mutex);
#else
	pthread_rwlock_wrlock(&t->rwlock);
#endif

	int ret = _avl_removeroot(t);

#ifdef AVL_LOCK_WITH_MUTEX
	pthread_mutex_unlock(&t->mutex);
#else
	pthread_rwlock_unlock(&t->rwlock);
#endif
	return ret;
}

/* 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) {
	int x, c = 0;
	if (!t->root)
		return 0;
	x = t->compar(t->root, a);
	if (a != b) {
		if (x < 0) {
			x = t->compar(t->root, b);
			if (x > 0)
				x = 0;
		}
	}
	if (x >= 0) {
		/* search in the left subtree */
		avl_tree left_subtree;
		if ((left_subtree.root = t->root->left)) {
			left_subtree.compar = t->compar;
			if (!(c = _avl_range(&left_subtree, a, b, iter, ret)))
				if (x > 0)
					return 0;
		}
	}
	if (x == 0) {
		if (!(c = iter(t->root))) {
			if (ret)
				*ret = t->root;
			return 0;
		}
	}
	if (x <= 0) {
		/* search in the right subtree */
		avl_tree right_subtree;
		if ((right_subtree.root = t->root->right)) {
			right_subtree.compar = t->compar;
			if (!(c = _avl_range(&right_subtree, a, b, iter, ret)))
				if (x < 0)
					return 0;
		}
	}
	return c;
}

int avl_range(avl_tree* t, avl* a, avl* b, int (*iter)(avl*), avl** ret) {
#ifdef AVL_LOCK_WITH_MUTEX
	pthread_mutex_lock(&t->mutex);
#else
	pthread_rwlock_wrlock(&t->rwlock);
#endif

	int ret2 = _avl_range(t, a, b, iter, ret);

#ifdef AVL_LOCK_WITH_MUTEX
	pthread_mutex_unlock(&t->mutex);
#else
	pthread_rwlock_unlock(&t->rwlock);
#endif

	return ret2;
}

/* 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* a), avl** ret) {
	return avl_range(t, a, a, iter, ret);
}

void avl_init(avl_tree* t, int (*compar)(void* a, void* b)) {
	t->root = NULL;
	t->compar = compar;
#ifdef AVL_LOCK_WITH_MUTEX
	pthread_mutex_init(&t->mutex, NULL);
#else
	pthread_rwlock_init(&t->rwlock, NULL);
#endif
}