1/* SPDX-License-Identifier: GPL-2.0-or-later */
2/*
3  Red Black Trees
4  (C) 1999  Andrea Arcangeli <andrea@suse.de>
5  (C) 2002  David Woodhouse <dwmw2@infradead.org>
6  (C) 2012  Michel Lespinasse <walken@google.com>
7
8
9  linux/include/linux/rbtree_augmented.h
10*/
11
12#ifndef _LINUX_RBTREE_AUGMENTED_H
13#define _LINUX_RBTREE_AUGMENTED_H
14
15#include <linux/compiler.h>
16#include <linux/rbtree.h>
17#include <linux/rcupdate.h>
18
19/*
20 * Please note - only struct rb_augment_callbacks and the prototypes for
21 * rb_insert_augmented() and rb_erase_augmented() are intended to be public.
22 * The rest are implementation details you are not expected to depend on.
23 *
24 * See Documentation/core-api/rbtree.rst for documentation and samples.
25 */
26
27struct rb_augment_callbacks {
28	void (*propagate)(struct rb_node *node, struct rb_node *stop);
29	void (*copy)(struct rb_node *old, struct rb_node *new);
30	void (*rotate)(struct rb_node *old, struct rb_node *new);
31};
32
33extern void __rb_insert_augmented(struct rb_node *node, struct rb_root *root,
34	void (*augment_rotate)(struct rb_node *old, struct rb_node *new));
35
36/*
37 * Fixup the rbtree and update the augmented information when rebalancing.
38 *
39 * On insertion, the user must update the augmented information on the path
40 * leading to the inserted node, then call rb_link_node() as usual and
41 * rb_insert_augmented() instead of the usual rb_insert_color() call.
42 * If rb_insert_augmented() rebalances the rbtree, it will callback into
43 * a user provided function to update the augmented information on the
44 * affected subtrees.
45 */
46static inline void
47rb_insert_augmented(struct rb_node *node, struct rb_root *root,
48		    const struct rb_augment_callbacks *augment)
49{
50	__rb_insert_augmented(node, root, augment->rotate);
51}
52
53static inline void
54rb_insert_augmented_cached(struct rb_node *node,
55			   struct rb_root_cached *root, bool newleft,
56			   const struct rb_augment_callbacks *augment)
57{
58	if (newleft)
59		root->rb_leftmost = node;
60	rb_insert_augmented(node, &root->rb_root, augment);
61}
62
63static __always_inline struct rb_node *
64rb_add_augmented_cached(struct rb_node *node, struct rb_root_cached *tree,
65			bool (*less)(struct rb_node *, const struct rb_node *),
66			const struct rb_augment_callbacks *augment)
67{
68	struct rb_node **link = &tree->rb_root.rb_node;
69	struct rb_node *parent = NULL;
70	bool leftmost = true;
71
72	while (*link) {
73		parent = *link;
74		if (less(node, parent)) {
75			link = &parent->rb_left;
76		} else {
77			link = &parent->rb_right;
78			leftmost = false;
79		}
80	}
81
82	rb_link_node(node, parent, link);
83	augment->propagate(parent, NULL); /* suboptimal */
84	rb_insert_augmented_cached(node, tree, leftmost, augment);
85
86	return leftmost ? node : NULL;
87}
88
89/*
90 * Template for declaring augmented rbtree callbacks (generic case)
91 *
92 * RBSTATIC:    'static' or empty
93 * RBNAME:      name of the rb_augment_callbacks structure
94 * RBSTRUCT:    struct type of the tree nodes
95 * RBFIELD:     name of struct rb_node field within RBSTRUCT
96 * RBAUGMENTED: name of field within RBSTRUCT holding data for subtree
97 * RBCOMPUTE:   name of function that recomputes the RBAUGMENTED data
98 */
99
100#define RB_DECLARE_CALLBACKS(RBSTATIC, RBNAME,				\
101			     RBSTRUCT, RBFIELD, RBAUGMENTED, RBCOMPUTE)	\
102static inline void							\
103RBNAME ## _propagate(struct rb_node *rb, struct rb_node *stop)		\
104{									\
105	while (rb != stop) {						\
106		RBSTRUCT *node = rb_entry(rb, RBSTRUCT, RBFIELD);	\
107		if (RBCOMPUTE(node, true))				\
108			break;						\
109		rb = rb_parent(&node->RBFIELD);				\
110	}								\
111}									\
112static inline void							\
113RBNAME ## _copy(struct rb_node *rb_old, struct rb_node *rb_new)		\
114{									\
115	RBSTRUCT *old = rb_entry(rb_old, RBSTRUCT, RBFIELD);		\
116	RBSTRUCT *new = rb_entry(rb_new, RBSTRUCT, RBFIELD);		\
117	new->RBAUGMENTED = old->RBAUGMENTED;				\
118}									\
119static void								\
120RBNAME ## _rotate(struct rb_node *rb_old, struct rb_node *rb_new)	\
121{									\
122	RBSTRUCT *old = rb_entry(rb_old, RBSTRUCT, RBFIELD);		\
123	RBSTRUCT *new = rb_entry(rb_new, RBSTRUCT, RBFIELD);		\
124	new->RBAUGMENTED = old->RBAUGMENTED;				\
125	RBCOMPUTE(old, false);						\
126}									\
127RBSTATIC const struct rb_augment_callbacks RBNAME = {			\
128	.propagate = RBNAME ## _propagate,				\
129	.copy = RBNAME ## _copy,					\
130	.rotate = RBNAME ## _rotate					\
131};
132
133/*
134 * Template for declaring augmented rbtree callbacks,
135 * computing RBAUGMENTED scalar as max(RBCOMPUTE(node)) for all subtree nodes.
136 *
137 * RBSTATIC:    'static' or empty
138 * RBNAME:      name of the rb_augment_callbacks structure
139 * RBSTRUCT:    struct type of the tree nodes
140 * RBFIELD:     name of struct rb_node field within RBSTRUCT
141 * RBTYPE:      type of the RBAUGMENTED field
142 * RBAUGMENTED: name of RBTYPE field within RBSTRUCT holding data for subtree
143 * RBCOMPUTE:   name of function that returns the per-node RBTYPE scalar
144 */
145
146#define RB_DECLARE_CALLBACKS_MAX(RBSTATIC, RBNAME, RBSTRUCT, RBFIELD,	      \
147				 RBTYPE, RBAUGMENTED, RBCOMPUTE)	      \
148static inline bool RBNAME ## _compute_max(RBSTRUCT *node, bool exit)	      \
149{									      \
150	RBSTRUCT *child;						      \
151	RBTYPE max = RBCOMPUTE(node);					      \
152	if (node->RBFIELD.rb_left) {					      \
153		child = rb_entry(node->RBFIELD.rb_left, RBSTRUCT, RBFIELD);   \
154		if (child->RBAUGMENTED > max)				      \
155			max = child->RBAUGMENTED;			      \
156	}								      \
157	if (node->RBFIELD.rb_right) {					      \
158		child = rb_entry(node->RBFIELD.rb_right, RBSTRUCT, RBFIELD);  \
159		if (child->RBAUGMENTED > max)				      \
160			max = child->RBAUGMENTED;			      \
161	}								      \
162	if (exit && node->RBAUGMENTED == max)				      \
163		return true;						      \
164	node->RBAUGMENTED = max;					      \
165	return false;							      \
166}									      \
167RB_DECLARE_CALLBACKS(RBSTATIC, RBNAME,					      \
168		     RBSTRUCT, RBFIELD, RBAUGMENTED, RBNAME ## _compute_max)
169
170
171#define	RB_RED		0
172#define	RB_BLACK	1
173
174#define __rb_parent(pc)    ((struct rb_node *)(pc & ~3))
175
176#define __rb_color(pc)     ((pc) & 1)
177#define __rb_is_black(pc)  __rb_color(pc)
178#define __rb_is_red(pc)    (!__rb_color(pc))
179#define rb_color(rb)       __rb_color((rb)->__rb_parent_color)
180#define rb_is_red(rb)      __rb_is_red((rb)->__rb_parent_color)
181#define rb_is_black(rb)    __rb_is_black((rb)->__rb_parent_color)
182
183static inline void rb_set_parent(struct rb_node *rb, struct rb_node *p)
184{
185	rb->__rb_parent_color = rb_color(rb) + (unsigned long)p;
186}
187
188static inline void rb_set_parent_color(struct rb_node *rb,
189				       struct rb_node *p, int color)
190{
191	rb->__rb_parent_color = (unsigned long)p + color;
192}
193
194static inline void
195__rb_change_child(struct rb_node *old, struct rb_node *new,
196		  struct rb_node *parent, struct rb_root *root)
197{
198	if (parent) {
199		if (parent->rb_left == old)
200			WRITE_ONCE(parent->rb_left, new);
201		else
202			WRITE_ONCE(parent->rb_right, new);
203	} else
204		WRITE_ONCE(root->rb_node, new);
205}
206
207static inline void
208__rb_change_child_rcu(struct rb_node *old, struct rb_node *new,
209		      struct rb_node *parent, struct rb_root *root)
210{
211	if (parent) {
212		if (parent->rb_left == old)
213			rcu_assign_pointer(parent->rb_left, new);
214		else
215			rcu_assign_pointer(parent->rb_right, new);
216	} else
217		rcu_assign_pointer(root->rb_node, new);
218}
219
220extern void __rb_erase_color(struct rb_node *parent, struct rb_root *root,
221	void (*augment_rotate)(struct rb_node *old, struct rb_node *new));
222
223static __always_inline struct rb_node *
224__rb_erase_augmented(struct rb_node *node, struct rb_root *root,
225		     const struct rb_augment_callbacks *augment)
226{
227	struct rb_node *child = node->rb_right;
228	struct rb_node *tmp = node->rb_left;
229	struct rb_node *parent, *rebalance;
230	unsigned long pc;
231
232	if (!tmp) {
233		/*
234		 * Case 1: node to erase has no more than 1 child (easy!)
235		 *
236		 * Note that if there is one child it must be red due to 5)
237		 * and node must be black due to 4). We adjust colors locally
238		 * so as to bypass __rb_erase_color() later on.
239		 */
240		pc = node->__rb_parent_color;
241		parent = __rb_parent(pc);
242		__rb_change_child(node, child, parent, root);
243		if (child) {
244			child->__rb_parent_color = pc;
245			rebalance = NULL;
246		} else
247			rebalance = __rb_is_black(pc) ? parent : NULL;
248		tmp = parent;
249	} else if (!child) {
250		/* Still case 1, but this time the child is node->rb_left */
251		tmp->__rb_parent_color = pc = node->__rb_parent_color;
252		parent = __rb_parent(pc);
253		__rb_change_child(node, tmp, parent, root);
254		rebalance = NULL;
255		tmp = parent;
256	} else {
257		struct rb_node *successor = child, *child2;
258
259		tmp = child->rb_left;
260		if (!tmp) {
261			/*
262			 * Case 2: node's successor is its right child
263			 *
264			 *    (n)          (s)
265			 *    / \          / \
266			 *  (x) (s)  ->  (x) (c)
267			 *        \
268			 *        (c)
269			 */
270			parent = successor;
271			child2 = successor->rb_right;
272
273			augment->copy(node, successor);
274		} else {
275			/*
276			 * Case 3: node's successor is leftmost under
277			 * node's right child subtree
278			 *
279			 *    (n)          (s)
280			 *    / \          / \
281			 *  (x) (y)  ->  (x) (y)
282			 *      /            /
283			 *    (p)          (p)
284			 *    /            /
285			 *  (s)          (c)
286			 *    \
287			 *    (c)
288			 */
289			do {
290				parent = successor;
291				successor = tmp;
292				tmp = tmp->rb_left;
293			} while (tmp);
294			child2 = successor->rb_right;
295			WRITE_ONCE(parent->rb_left, child2);
296			WRITE_ONCE(successor->rb_right, child);
297			rb_set_parent(child, successor);
298
299			augment->copy(node, successor);
300			augment->propagate(parent, successor);
301		}
302
303		tmp = node->rb_left;
304		WRITE_ONCE(successor->rb_left, tmp);
305		rb_set_parent(tmp, successor);
306
307		pc = node->__rb_parent_color;
308		tmp = __rb_parent(pc);
309		__rb_change_child(node, successor, tmp, root);
310
311		if (child2) {
312			rb_set_parent_color(child2, parent, RB_BLACK);
313			rebalance = NULL;
314		} else {
315			rebalance = rb_is_black(successor) ? parent : NULL;
316		}
317		successor->__rb_parent_color = pc;
318		tmp = successor;
319	}
320
321	augment->propagate(tmp, NULL);
322	return rebalance;
323}
324
325static __always_inline void
326rb_erase_augmented(struct rb_node *node, struct rb_root *root,
327		   const struct rb_augment_callbacks *augment)
328{
329	struct rb_node *rebalance = __rb_erase_augmented(node, root, augment);
330	if (rebalance)
331		__rb_erase_color(rebalance, root, augment->rotate);
332}
333
334static __always_inline void
335rb_erase_augmented_cached(struct rb_node *node, struct rb_root_cached *root,
336			  const struct rb_augment_callbacks *augment)
337{
338	if (root->rb_leftmost == node)
339		root->rb_leftmost = rb_next(node);
340	rb_erase_augmented(node, &root->rb_root, augment);
341}
342
343#endif	/* _LINUX_RBTREE_AUGMENTED_H */
344