/*
   * lib/btree.c	- Simple In-memory B+Tree
   *
   * As should be obvious for Linux kernel code, license is GPLv2
   *
   * Copyright (c) 2007-2008 Joern Engel <joern@logfs.org>
   * Bits and pieces stolen from Peter Zijlstra's code, which is
   * Copyright 2007, Red Hat Inc. Peter Zijlstra <pzijlstr@redhat.com>
   * GPLv2
   *
   * see http://programming.kicks-ass.net/kernel-patches/vma_lookup/btree.patch
   *
   * A relatively simple B+Tree implementation.  I have written it as a learning

   * exercise to understand how B+Trees work.  Turned out to be useful as well.

   *
   * B+Trees can be used similar to Linux radix trees (which don't have anything
   * in common with textbook radix trees, beware).  Prerequisite for them working
   * well is that access to a random tree node is much faster than a large number
   * of operations within each node.
   *
   * Disks have fulfilled the prerequisite for a long time.  More recently DRAM
   * has gained similar properties, as memory access times, when measured in cpu
   * cycles, have increased.  Cacheline sizes have increased as well, which also
   * helps B+Trees.
   *
   * Compared to radix trees, B+Trees are more efficient when dealing with a
   * sparsely populated address space.  Between 25% and 50% of the memory is
   * occupied with valid pointers.  When densely populated, radix trees contain
   * ~98% pointers - hard to beat.  Very sparse radix trees contain only ~2%
   * pointers.
   *
   * This particular implementation stores pointers identified by a long value.
   * Storing NULL pointers is illegal, lookup will return NULL when no entry
   * was found.
   *
   * A tricks was used that is not commonly found in textbooks.  The lowest
   * values are to the right, not to the left.  All used slots within a node
   * are on the left, all unused slots contain NUL values.  Most operations
   * simply loop once over all slots and terminate on the first NUL.
   */
  
  #include <linux/btree.h>
  #include <linux/cache.h>
  #include <linux/kernel.h>
  #include <linux/slab.h>
  #include <linux/module.h>
  
  #define MAX(a, b) ((a) > (b) ? (a) : (b))
  #define NODESIZE MAX(L1_CACHE_BYTES, 128)
  
  struct btree_geo {
  	int keylen;
  	int no_pairs;
  	int no_longs;
  };
  
  struct btree_geo btree_geo32 = {
  	.keylen = 1,
  	.no_pairs = NODESIZE / sizeof(long) / 2,
  	.no_longs = NODESIZE / sizeof(long) / 2,
  };
  EXPORT_SYMBOL_GPL(btree_geo32);
  
  #define LONG_PER_U64 (64 / BITS_PER_LONG)
  struct btree_geo btree_geo64 = {
  	.keylen = LONG_PER_U64,
  	.no_pairs = NODESIZE / sizeof(long) / (1 + LONG_PER_U64),
  	.no_longs = LONG_PER_U64 * (NODESIZE / sizeof(long) / (1 + LONG_PER_U64)),
  };
  EXPORT_SYMBOL_GPL(btree_geo64);
  
  struct btree_geo btree_geo128 = {
  	.keylen = 2 * LONG_PER_U64,
  	.no_pairs = NODESIZE / sizeof(long) / (1 + 2 * LONG_PER_U64),
  	.no_longs = 2 * LONG_PER_U64 * (NODESIZE / sizeof(long) / (1 + 2 * LONG_PER_U64)),
  };
  EXPORT_SYMBOL_GPL(btree_geo128);
  
  static struct kmem_cache *btree_cachep;
  
  void *btree_alloc(gfp_t gfp_mask, void *pool_data)
  {
  	return kmem_cache_alloc(btree_cachep, gfp_mask);
  }
  EXPORT_SYMBOL_GPL(btree_alloc);
  
  void btree_free(void *element, void *pool_data)
  {
  	kmem_cache_free(btree_cachep, element);
  }
  EXPORT_SYMBOL_GPL(btree_free);
  
  static unsigned long *btree_node_alloc(struct btree_head *head, gfp_t gfp)
  {
  	unsigned long *node;
  
  	node = mempool_alloc(head->mempool, gfp);

  	if (likely(node))
  		memset(node, 0, NODESIZE);

  	return node;
  }
  
  static int longcmp(const unsigned long *l1, const unsigned long *l2, size_t n)
  {
  	size_t i;
  
  	for (i = 0; i < n; i++) {
  		if (l1[i] < l2[i])
  			return -1;
  		if (l1[i] > l2[i])
  			return 1;
  	}
  	return 0;
  }
  
  static unsigned long *longcpy(unsigned long *dest, const unsigned long *src,
  		size_t n)
  {
  	size_t i;
  
  	for (i = 0; i < n; i++)
  		dest[i] = src[i];
  	return dest;
  }
  
  static unsigned long *longset(unsigned long *s, unsigned long c, size_t n)
  {
  	size_t i;
  
  	for (i = 0; i < n; i++)
  		s[i] = c;
  	return s;
  }
  
  static void dec_key(struct btree_geo *geo, unsigned long *key)
  {
  	unsigned long val;
  	int i;
  
  	for (i = geo->keylen - 1; i >= 0; i--) {
  		val = key[i];
  		key[i] = val - 1;
  		if (val)
  			break;
  	}
  }
  
  static unsigned long *bkey(struct btree_geo *geo, unsigned long *node, int n)
  {
  	return &node[n * geo->keylen];
  }
  
  static void *bval(struct btree_geo *geo, unsigned long *node, int n)
  {
  	return (void *)node[geo->no_longs + n];
  }
  
  static void setkey(struct btree_geo *geo, unsigned long *node, int n,
  		   unsigned long *key)
  {
  	longcpy(bkey(geo, node, n), key, geo->keylen);
  }
  
  static void setval(struct btree_geo *geo, unsigned long *node, int n,
  		   void *val)
  {
  	node[geo->no_longs + n] = (unsigned long) val;
  }
  
  static void clearpair(struct btree_geo *geo, unsigned long *node, int n)
  {
  	longset(bkey(geo, node, n), 0, geo->keylen);
  	node[geo->no_longs + n] = 0;
  }
  
  static inline void __btree_init(struct btree_head *head)
  {
  	head->node = NULL;
  	head->height = 0;
  }
  
  void btree_init_mempool(struct btree_head *head, mempool_t *mempool)
  {
  	__btree_init(head);
  	head->mempool = mempool;
  }
  EXPORT_SYMBOL_GPL(btree_init_mempool);
  
  int btree_init(struct btree_head *head)
  {
  	__btree_init(head);
  	head->mempool = mempool_create(0, btree_alloc, btree_free, NULL);
  	if (!head->mempool)
  		return -ENOMEM;
  	return 0;
  }
  EXPORT_SYMBOL_GPL(btree_init);
  
  void btree_destroy(struct btree_head *head)
  {
  	mempool_destroy(head->mempool);
  	head->mempool = NULL;
  }
  EXPORT_SYMBOL_GPL(btree_destroy);
  
  void *btree_last(struct btree_head *head, struct btree_geo *geo,
  		 unsigned long *key)
  {
  	int height = head->height;
  	unsigned long *node = head->node;
  
  	if (height == 0)
  		return NULL;
  
  	for ( ; height > 1; height--)
  		node = bval(geo, node, 0);
  
  	longcpy(key, bkey(geo, node, 0), geo->keylen);
  	return bval(geo, node, 0);
  }
  EXPORT_SYMBOL_GPL(btree_last);
  
  static int keycmp(struct btree_geo *geo, unsigned long *node, int pos,
  		  unsigned long *key)
  {
  	return longcmp(bkey(geo, node, pos), key, geo->keylen);
  }
  
  static int keyzero(struct btree_geo *geo, unsigned long *key)
  {
  	int i;
  
  	for (i = 0; i < geo->keylen; i++)
  		if (key[i])
  			return 0;
  
  	return 1;
  }
  
  void *btree_lookup(struct btree_head *head, struct btree_geo *geo,
  		unsigned long *key)
  {
  	int i, height = head->height;
  	unsigned long *node = head->node;
  
  	if (height == 0)
  		return NULL;
  
  	for ( ; height > 1; height--) {
  		for (i = 0; i < geo->no_pairs; i++)
  			if (keycmp(geo, node, i, key) <= 0)
  				break;
  		if (i == geo->no_pairs)
  			return NULL;
  		node = bval(geo, node, i);
  		if (!node)
  			return NULL;
  	}
  
  	if (!node)
  		return NULL;
  
  	for (i = 0; i < geo->no_pairs; i++)
  		if (keycmp(geo, node, i, key) == 0)
  			return bval(geo, node, i);
  	return NULL;
  }
  EXPORT_SYMBOL_GPL(btree_lookup);
  
  int btree_update(struct btree_head *head, struct btree_geo *geo,
  		 unsigned long *key, void *val)
  {
  	int i, height = head->height;
  	unsigned long *node = head->node;
  
  	if (height == 0)
  		return -ENOENT;
  
  	for ( ; height > 1; height--) {
  		for (i = 0; i < geo->no_pairs; i++)
  			if (keycmp(geo, node, i, key) <= 0)
  				break;
  		if (i == geo->no_pairs)
  			return -ENOENT;
  		node = bval(geo, node, i);
  		if (!node)
  			return -ENOENT;
  	}
  
  	if (!node)
  		return -ENOENT;
  
  	for (i = 0; i < geo->no_pairs; i++)
  		if (keycmp(geo, node, i, key) == 0) {
  			setval(geo, node, i, val);
  			return 0;
  		}
  	return -ENOENT;
  }
  EXPORT_SYMBOL_GPL(btree_update);
  
  /*
   * Usually this function is quite similar to normal lookup.  But the key of
   * a parent node may be smaller than the smallest key of all its siblings.
   * In such a case we cannot just return NULL, as we have only proven that no
   * key smaller than __key, but larger than this parent key exists.
   * So we set __key to the parent key and retry.  We have to use the smallest
   * such parent key, which is the last parent key we encountered.
   */
  void *btree_get_prev(struct btree_head *head, struct btree_geo *geo,
  		     unsigned long *__key)
  {
  	int i, height;
  	unsigned long *node, *oldnode;
  	unsigned long *retry_key = NULL, key[geo->keylen];
  
  	if (keyzero(geo, __key))
  		return NULL;
  
  	if (head->height == 0)
  		return NULL;
  retry:
  	longcpy(key, __key, geo->keylen);
  	dec_key(geo, key);
  
  	node = head->node;
  	for (height = head->height ; height > 1; height--) {
  		for (i = 0; i < geo->no_pairs; i++)
  			if (keycmp(geo, node, i, key) <= 0)
  				break;
  		if (i == geo->no_pairs)
  			goto miss;
  		oldnode = node;
  		node = bval(geo, node, i);
  		if (!node)
  			goto miss;
  		retry_key = bkey(geo, oldnode, i);
  	}
  
  	if (!node)
  		goto miss;
  
  	for (i = 0; i < geo->no_pairs; i++) {
  		if (keycmp(geo, node, i, key) <= 0) {
  			if (bval(geo, node, i)) {
  				longcpy(__key, bkey(geo, node, i), geo->keylen);
  				return bval(geo, node, i);
  			} else
  				goto miss;
  		}
  	}
  miss:
  	if (retry_key) {
  		__key = retry_key;
  		retry_key = NULL;
  		goto retry;
  	}
  	return NULL;
  }
  
  static int getpos(struct btree_geo *geo, unsigned long *node,
  		unsigned long *key)
  {
  	int i;
  
  	for (i = 0; i < geo->no_pairs; i++) {
  		if (keycmp(geo, node, i, key) <= 0)
  			break;
  	}
  	return i;
  }
  
  static int getfill(struct btree_geo *geo, unsigned long *node, int start)
  {
  	int i;
  
  	for (i = start; i < geo->no_pairs; i++)
  		if (!bval(geo, node, i))
  			break;
  	return i;
  }
  
  /*
   * locate the correct leaf node in the btree
   */
  static unsigned long *find_level(struct btree_head *head, struct btree_geo *geo,
  		unsigned long *key, int level)
  {
  	unsigned long *node = head->node;
  	int i, height;
  
  	for (height = head->height; height > level; height--) {
  		for (i = 0; i < geo->no_pairs; i++)
  			if (keycmp(geo, node, i, key) <= 0)
  				break;
  
  		if ((i == geo->no_pairs) || !bval(geo, node, i)) {
  			/* right-most key is too large, update it */
  			/* FIXME: If the right-most key on higher levels is
  			 * always zero, this wouldn't be necessary. */
  			i--;
  			setkey(geo, node, i, key);
  		}
  		BUG_ON(i < 0);
  		node = bval(geo, node, i);
  	}
  	BUG_ON(!node);
  	return node;
  }
  
  static int btree_grow(struct btree_head *head, struct btree_geo *geo,
  		      gfp_t gfp)
  {
  	unsigned long *node;
  	int fill;
  
  	node = btree_node_alloc(head, gfp);
  	if (!node)
  		return -ENOMEM;
  	if (head->node) {
  		fill = getfill(geo, head->node, 0);
  		setkey(geo, node, 0, bkey(geo, head->node, fill - 1));
  		setval(geo, node, 0, head->node);
  	}
  	head->node = node;
  	head->height++;
  	return 0;
  }
  
  static void btree_shrink(struct btree_head *head, struct btree_geo *geo)
  {
  	unsigned long *node;
  	int fill;
  
  	if (head->height <= 1)
  		return;
  
  	node = head->node;
  	fill = getfill(geo, node, 0);
  	BUG_ON(fill > 1);
  	head->node = bval(geo, node, 0);
  	head->height--;
  	mempool_free(node, head->mempool);
  }
  
  static int btree_insert_level(struct btree_head *head, struct btree_geo *geo,
  			      unsigned long *key, void *val, int level,
  			      gfp_t gfp)
  {
  	unsigned long *node;
  	int i, pos, fill, err;
  
  	BUG_ON(!val);
  	if (head->height < level) {
  		err = btree_grow(head, geo, gfp);
  		if (err)
  			return err;
  	}
  
  retry:
  	node = find_level(head, geo, key, level);
  	pos = getpos(geo, node, key);
  	fill = getfill(geo, node, pos);
  	/* two identical keys are not allowed */
  	BUG_ON(pos < fill && keycmp(geo, node, pos, key) == 0);
  
  	if (fill == geo->no_pairs) {
  		/* need to split node */
  		unsigned long *new;
  
  		new = btree_node_alloc(head, gfp);
  		if (!new)
  			return -ENOMEM;
  		err = btree_insert_level(head, geo,
  				bkey(geo, node, fill / 2 - 1),
  				new, level + 1, gfp);
  		if (err) {
  			mempool_free(new, head->mempool);
  			return err;
  		}
  		for (i = 0; i < fill / 2; i++) {
  			setkey(geo, new, i, bkey(geo, node, i));
  			setval(geo, new, i, bval(geo, node, i));
  			setkey(geo, node, i, bkey(geo, node, i + fill / 2));
  			setval(geo, node, i, bval(geo, node, i + fill / 2));
  			clearpair(geo, node, i + fill / 2);
  		}
  		if (fill & 1) {
  			setkey(geo, node, i, bkey(geo, node, fill - 1));
  			setval(geo, node, i, bval(geo, node, fill - 1));
  			clearpair(geo, node, fill - 1);
  		}
  		goto retry;
  	}
  	BUG_ON(fill >= geo->no_pairs);
  
  	/* shift and insert */
  	for (i = fill; i > pos; i--) {
  		setkey(geo, node, i, bkey(geo, node, i - 1));
  		setval(geo, node, i, bval(geo, node, i - 1));
  	}
  	setkey(geo, node, pos, key);
  	setval(geo, node, pos, val);
  
  	return 0;
  }
  
  int btree_insert(struct btree_head *head, struct btree_geo *geo,
  		unsigned long *key, void *val, gfp_t gfp)
  {
  	return btree_insert_level(head, geo, key, val, 1, gfp);
  }
  EXPORT_SYMBOL_GPL(btree_insert);
  
  static void *btree_remove_level(struct btree_head *head, struct btree_geo *geo,
  		unsigned long *key, int level);
  static void merge(struct btree_head *head, struct btree_geo *geo, int level,
  		unsigned long *left, int lfill,
  		unsigned long *right, int rfill,
  		unsigned long *parent, int lpos)
  {
  	int i;
  
  	for (i = 0; i < rfill; i++) {
  		/* Move all keys to the left */
  		setkey(geo, left, lfill + i, bkey(geo, right, i));
  		setval(geo, left, lfill + i, bval(geo, right, i));
  	}
  	/* Exchange left and right child in parent */
  	setval(geo, parent, lpos, right);
  	setval(geo, parent, lpos + 1, left);
  	/* Remove left (formerly right) child from parent */
  	btree_remove_level(head, geo, bkey(geo, parent, lpos), level + 1);
  	mempool_free(right, head->mempool);
  }
  
  static void rebalance(struct btree_head *head, struct btree_geo *geo,
  		unsigned long *key, int level, unsigned long *child, int fill)
  {
  	unsigned long *parent, *left = NULL, *right = NULL;
  	int i, no_left, no_right;
  
  	if (fill == 0) {

  		/* Because we don't steal entries from a neighbour, this case

  		 * can happen.  Parent node contains a single child, this
  		 * node, so merging with a sibling never happens.
  		 */
  		btree_remove_level(head, geo, key, level + 1);
  		mempool_free(child, head->mempool);
  		return;
  	}
  
  	parent = find_level(head, geo, key, level + 1);
  	i = getpos(geo, parent, key);
  	BUG_ON(bval(geo, parent, i) != child);
  
  	if (i > 0) {
  		left = bval(geo, parent, i - 1);
  		no_left = getfill(geo, left, 0);
  		if (fill + no_left <= geo->no_pairs) {
  			merge(head, geo, level,
  					left, no_left,
  					child, fill,
  					parent, i - 1);
  			return;
  		}
  	}
  	if (i + 1 < getfill(geo, parent, i)) {
  		right = bval(geo, parent, i + 1);
  		no_right = getfill(geo, right, 0);
  		if (fill + no_right <= geo->no_pairs) {
  			merge(head, geo, level,
  					child, fill,
  					right, no_right,
  					parent, i);
  			return;
  		}
  	}
  	/*
  	 * We could also try to steal one entry from the left or right
  	 * neighbor.  By not doing so we changed the invariant from
  	 * "all nodes are at least half full" to "no two neighboring
  	 * nodes can be merged".  Which means that the average fill of
  	 * all nodes is still half or better.
  	 */
  }
  
  static void *btree_remove_level(struct btree_head *head, struct btree_geo *geo,
  		unsigned long *key, int level)
  {
  	unsigned long *node;
  	int i, pos, fill;
  	void *ret;
  
  	if (level > head->height) {
  		/* we recursed all the way up */
  		head->height = 0;
  		head->node = NULL;
  		return NULL;
  	}
  
  	node = find_level(head, geo, key, level);
  	pos = getpos(geo, node, key);
  	fill = getfill(geo, node, pos);
  	if ((level == 1) && (keycmp(geo, node, pos, key) != 0))
  		return NULL;
  	ret = bval(geo, node, pos);
  
  	/* remove and shift */
  	for (i = pos; i < fill - 1; i++) {
  		setkey(geo, node, i, bkey(geo, node, i + 1));
  		setval(geo, node, i, bval(geo, node, i + 1));
  	}
  	clearpair(geo, node, fill - 1);
  
  	if (fill - 1 < geo->no_pairs / 2) {
  		if (level < head->height)
  			rebalance(head, geo, key, level, node, fill - 1);
  		else if (fill - 1 == 1)
  			btree_shrink(head, geo);
  	}
  
  	return ret;
  }
  
  void *btree_remove(struct btree_head *head, struct btree_geo *geo,
  		unsigned long *key)
  {
  	if (head->height == 0)
  		return NULL;
  
  	return btree_remove_level(head, geo, key, 1);
  }
  EXPORT_SYMBOL_GPL(btree_remove);
  
  int btree_merge(struct btree_head *target, struct btree_head *victim,
  		struct btree_geo *geo, gfp_t gfp)
  {
  	unsigned long key[geo->keylen];
  	unsigned long dup[geo->keylen];
  	void *val;
  	int err;
  
  	BUG_ON(target == victim);
  
  	if (!(target->node)) {
  		/* target is empty, just copy fields over */
  		target->node = victim->node;
  		target->height = victim->height;
  		__btree_init(victim);
  		return 0;
  	}
  
  	/* TODO: This needs some optimizations.  Currently we do three tree
  	 * walks to remove a single object from the victim.
  	 */
  	for (;;) {
  		if (!btree_last(victim, geo, key))
  			break;
  		val = btree_lookup(victim, geo, key);
  		err = btree_insert(target, geo, key, val, gfp);
  		if (err)
  			return err;
  		/* We must make a copy of the key, as the original will get
  		 * mangled inside btree_remove. */
  		longcpy(dup, key, geo->keylen);
  		btree_remove(victim, geo, dup);
  	}
  	return 0;
  }
  EXPORT_SYMBOL_GPL(btree_merge);
  
  static size_t __btree_for_each(struct btree_head *head, struct btree_geo *geo,
  			       unsigned long *node, unsigned long opaque,
  			       void (*func)(void *elem, unsigned long opaque,
  					    unsigned long *key, size_t index,
  					    void *func2),
  			       void *func2, int reap, int height, size_t count)
  {
  	int i;
  	unsigned long *child;
  
  	for (i = 0; i < geo->no_pairs; i++) {
  		child = bval(geo, node, i);
  		if (!child)
  			break;
  		if (height > 1)
  			count = __btree_for_each(head, geo, child, opaque,
  					func, func2, reap, height - 1, count);
  		else
  			func(child, opaque, bkey(geo, node, i), count++,
  					func2);
  	}
  	if (reap)
  		mempool_free(node, head->mempool);
  	return count;
  }
  
  static void empty(void *elem, unsigned long opaque, unsigned long *key,
  		  size_t index, void *func2)
  {
  }
  
  void visitorl(void *elem, unsigned long opaque, unsigned long *key,
  	      size_t index, void *__func)
  {
  	visitorl_t func = __func;
  
  	func(elem, opaque, *key, index);
  }
  EXPORT_SYMBOL_GPL(visitorl);
  
  void visitor32(void *elem, unsigned long opaque, unsigned long *__key,
  	       size_t index, void *__func)
  {
  	visitor32_t func = __func;
  	u32 *key = (void *)__key;
  
  	func(elem, opaque, *key, index);
  }
  EXPORT_SYMBOL_GPL(visitor32);
  
  void visitor64(void *elem, unsigned long opaque, unsigned long *__key,
  	       size_t index, void *__func)
  {
  	visitor64_t func = __func;
  	u64 *key = (void *)__key;
  
  	func(elem, opaque, *key, index);
  }
  EXPORT_SYMBOL_GPL(visitor64);
  
  void visitor128(void *elem, unsigned long opaque, unsigned long *__key,
  		size_t index, void *__func)
  {
  	visitor128_t func = __func;
  	u64 *key = (void *)__key;
  
  	func(elem, opaque, key[0], key[1], index);
  }
  EXPORT_SYMBOL_GPL(visitor128);
  
  size_t btree_visitor(struct btree_head *head, struct btree_geo *geo,
  		     unsigned long opaque,
  		     void (*func)(void *elem, unsigned long opaque,
  		     		  unsigned long *key,
  		     		  size_t index, void *func2),
  		     void *func2)
  {
  	size_t count = 0;
  
  	if (!func2)
  		func = empty;
  	if (head->node)
  		count = __btree_for_each(head, geo, head->node, opaque, func,
  				func2, 0, head->height, 0);
  	return count;
  }
  EXPORT_SYMBOL_GPL(btree_visitor);
  
  size_t btree_grim_visitor(struct btree_head *head, struct btree_geo *geo,
  			  unsigned long opaque,
  			  void (*func)(void *elem, unsigned long opaque,
  				       unsigned long *key,
  				       size_t index, void *func2),
  			  void *func2)
  {
  	size_t count = 0;
  
  	if (!func2)
  		func = empty;
  	if (head->node)
  		count = __btree_for_each(head, geo, head->node, opaque, func,
  				func2, 1, head->height, 0);
  	__btree_init(head);
  	return count;
  }
  EXPORT_SYMBOL_GPL(btree_grim_visitor);
  
  static int __init btree_module_init(void)
  {
  	btree_cachep = kmem_cache_create("btree_node", NODESIZE, 0,
  			SLAB_HWCACHE_ALIGN, NULL);
  	return 0;
  }
  
  static void __exit btree_module_exit(void)
  {
  	kmem_cache_destroy(btree_cachep);
  }
  
  /* If core code starts using btree, initialization should happen even earlier */
  module_init(btree_module_init);
  module_exit(btree_module_exit);
  
  MODULE_AUTHOR("Joern Engel <joern@logfs.org>");
  MODULE_AUTHOR("Johannes Berg <johannes@sipsolutions.net>");
  MODULE_LICENSE("GPL");