include/linux/rbtree_augmented.h

   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
  27 struct 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
  33 extern 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  */
  46 static inline void
  47 rb_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
  53 static inline void
  54 rb_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
  63 /*
  64  * Template for declaring augmented rbtree callbacks (generic case)
  65  *
  66  * RBSTATIC:    'static' or empty
  67  * RBNAME:      name of the rb_augment_callbacks structure
  68  * RBSTRUCT:    struct type of the tree nodes
  69  * RBFIELD:     name of struct rb_node field within RBSTRUCT
  70  * RBAUGMENTED: name of field within RBSTRUCT holding data for subtree
  71  * RBCOMPUTE:   name of function that recomputes the RBAUGMENTED data
  72  */
  73
  74 #define RB_DECLARE_CALLBACKS(RBSTATIC, RBNAME,                          \
  75                              RBSTRUCT, RBFIELD, RBAUGMENTED, RBCOMPUTE) \
  76 static inline void                                                      \
  77 RBNAME ## _propagate(struct rb_node *rb, struct rb_node *stop)          \
  78 {                                                                       \
  79         while (rb != stop) {                                            \
  80                 RBSTRUCT *node = rb_entry(rb, RBSTRUCT, RBFIELD);       \
  81                 if (RBCOMPUTE(node, true))                              \
  82                         break;                                          \
  83                 rb = rb_parent(&node->RBFIELD);                         \
  84         }                                                               \
  85 }                                                                       \
  86 static inline void                                                      \
  87 RBNAME ## _copy(struct rb_node *rb_old, struct rb_node *rb_new)         \
  88 {                                                                       \
  89         RBSTRUCT *old = rb_entry(rb_old, RBSTRUCT, RBFIELD);            \
  90         RBSTRUCT *new = rb_entry(rb_new, RBSTRUCT, RBFIELD);            \
  91         new->RBAUGMENTED = old->RBAUGMENTED;                            \
  92 }                                                                       \
  93 static void                                                             \
  94 RBNAME ## _rotate(struct rb_node *rb_old, struct rb_node *rb_new)       \
  95 {                                                                       \
  96         RBSTRUCT *old = rb_entry(rb_old, RBSTRUCT, RBFIELD);            \
  97         RBSTRUCT *new = rb_entry(rb_new, RBSTRUCT, RBFIELD);            \
  98         new->RBAUGMENTED = old->RBAUGMENTED;                            \
  99         RBCOMPUTE(old, false);                                          \
 100 }                                                                       \
 101 RBSTATIC const struct rb_augment_callbacks RBNAME = {                   \
 102         .propagate = RBNAME ## _propagate,                              \
 103         .copy = RBNAME ## _copy,                                        \
 104         .rotate = RBNAME ## _rotate                                     \
 105 };
 106
 107 /*
 108  * Template for declaring augmented rbtree callbacks,
 109  * computing RBAUGMENTED scalar as max(RBCOMPUTE(node)) for all subtree nodes.
 110  *
 111  * RBSTATIC:    'static' or empty
 112  * RBNAME:      name of the rb_augment_callbacks structure
 113  * RBSTRUCT:    struct type of the tree nodes
 114  * RBFIELD:     name of struct rb_node field within RBSTRUCT
 115  * RBTYPE:      type of the RBAUGMENTED field
 116  * RBAUGMENTED: name of RBTYPE field within RBSTRUCT holding data for subtree
 117  * RBCOMPUTE:   name of function that returns the per-node RBTYPE scalar
 118  */
 119
 120 #define RB_DECLARE_CALLBACKS_MAX(RBSTATIC, RBNAME, RBSTRUCT, RBFIELD,         \
 121                                  RBTYPE, RBAUGMENTED, RBCOMPUTE)              \
 122 static inline bool RBNAME ## _compute_max(RBSTRUCT *node, bool exit)          \
 123 {                                                                             \
 124         RBSTRUCT *child;                                                      \
 125         RBTYPE max = RBCOMPUTE(node);                                         \
 126         if (node->RBFIELD.rb_left) {                                          \
 127                 child = rb_entry(node->RBFIELD.rb_left, RBSTRUCT, RBFIELD);   \
 128                 if (child->RBAUGMENTED > max)                                 \
 129                         max = child->RBAUGMENTED;                             \
 130         }                                                                     \
 131         if (node->RBFIELD.rb_right) {                                         \
 132                 child = rb_entry(node->RBFIELD.rb_right, RBSTRUCT, RBFIELD);  \
 133                 if (child->RBAUGMENTED > max)                                 \
 134                         max = child->RBAUGMENTED;                             \
 135         }                                                                     \
 136         if (exit && node->RBAUGMENTED == max)                                 \
 137                 return true;                                                  \
 138         node->RBAUGMENTED = max;                                              \
 139         return false;                                                         \
 140 }                                                                             \
 141 RB_DECLARE_CALLBACKS(RBSTATIC, RBNAME,                                        \
 142                      RBSTRUCT, RBFIELD, RBAUGMENTED, RBNAME ## _compute_max)
 143
 144
 145 #define RB_RED          0
 146 #define RB_BLACK        1
 147
 148 #define __rb_parent(pc)    ((struct rb_node *)(pc & ~3))
 149
 150 #define __rb_color(pc)     ((pc) & 1)
 151 #define __rb_is_black(pc)  __rb_color(pc)
 152 #define __rb_is_red(pc)    (!__rb_color(pc))
 153 #define rb_color(rb)       __rb_color((rb)->__rb_parent_color)
 154 #define rb_is_red(rb)      __rb_is_red((rb)->__rb_parent_color)
 155 #define rb_is_black(rb)    __rb_is_black((rb)->__rb_parent_color)
 156
 157 static inline void rb_set_parent(struct rb_node *rb, struct rb_node *p)
 158 {
 159         rb->__rb_parent_color = rb_color(rb) | (unsigned long)p;
 160 }
 161
 162 static inline void rb_set_parent_color(struct rb_node *rb,
 163                                        struct rb_node *p, int color)
 164 {
 165         rb->__rb_parent_color = (unsigned long)p | color;
 166 }
 167
 168 static inline void
 169 __rb_change_child(struct rb_node *old, struct rb_node *new,
 170                   struct rb_node *parent, struct rb_root *root)
 171 {
 172         if (parent) {
 173                 if (parent->rb_left == old)
 174                         WRITE_ONCE(parent->rb_left, new);
 175                 else
 176                         WRITE_ONCE(parent->rb_right, new);
 177         } else
 178                 WRITE_ONCE(root->rb_node, new);
 179 }
 180
 181 static inline void
 182 __rb_change_child_rcu(struct rb_node *old, struct rb_node *new,
 183                       struct rb_node *parent, struct rb_root *root)
 184 {
 185         if (parent) {
 186                 if (parent->rb_left == old)
 187                         rcu_assign_pointer(parent->rb_left, new);
 188                 else
 189                         rcu_assign_pointer(parent->rb_right, new);
 190         } else
 191                 rcu_assign_pointer(root->rb_node, new);
 192 }
 193
 194 extern void __rb_erase_color(struct rb_node *parent, struct rb_root *root,
 195         void (*augment_rotate)(struct rb_node *old, struct rb_node *new));
 196
 197 static __always_inline struct rb_node *
 198 __rb_erase_augmented(struct rb_node *node, struct rb_root *root,
 199                      const struct rb_augment_callbacks *augment)
 200 {
 201         struct rb_node *child = node->rb_right;
 202         struct rb_node *tmp = node->rb_left;
 203         struct rb_node *parent, *rebalance;
 204         unsigned long pc;
 205
 206         if (!tmp) {
 207                 /*
 208                  * Case 1: node to erase has no more than 1 child (easy!)
 209                  *
 210                  * Note that if there is one child it must be red due to 5)
 211                  * and node must be black due to 4). We adjust colors locally
 212                  * so as to bypass __rb_erase_color() later on.
 213                  */
 214                 pc = node->__rb_parent_color;
 215                 parent = __rb_parent(pc);
 216                 __rb_change_child(node, child, parent, root);
 217                 if (child) {
 218                         child->__rb_parent_color = pc;
 219                         rebalance = NULL;
 220                 } else
 221                         rebalance = __rb_is_black(pc) ? parent : NULL;
 222                 tmp = parent;
 223         } else if (!child) {
 224                 /* Still case 1, but this time the child is node->rb_left */
 225                 tmp->__rb_parent_color = pc = node->__rb_parent_color;
 226                 parent = __rb_parent(pc);
 227                 __rb_change_child(node, tmp, parent, root);
 228                 rebalance = NULL;
 229                 tmp = parent;
 230         } else {
 231                 struct rb_node *successor = child, *child2;
 232
 233                 tmp = child->rb_left;
 234                 if (!tmp) {
 235                         /*
 236                          * Case 2: node's successor is its right child
 237                          *
 238                          *    (n)          (s)
 239                          *    / \          / \
 240                          *  (x) (s)  ->  (x) (c)
 241                          *        \
 242                          *        (c)
 243                          */
 244                         parent = successor;
 245                         child2 = successor->rb_right;
 246
 247                         augment->copy(node, successor);
 248                 } else {
 249                         /*
 250                          * Case 3: node's successor is leftmost under
 251                          * node's right child subtree
 252                          *
 253                          *    (n)          (s)
 254                          *    / \          / \
 255                          *  (x) (y)  ->  (x) (y)
 256                          *      /            /
 257                          *    (p)          (p)
 258                          *    /            /
 259                          *  (s)          (c)
 260                          *    \
 261                          *    (c)
 262                          */
 263                         do {
 264                                 parent = successor;
 265                                 successor = tmp;
 266                                 tmp = tmp->rb_left;
 267                         } while (tmp);
 268                         child2 = successor->rb_right;
 269                         WRITE_ONCE(parent->rb_left, child2);
 270                         WRITE_ONCE(successor->rb_right, child);
 271                         rb_set_parent(child, successor);
 272
 273                         augment->copy(node, successor);
 274                         augment->propagate(parent, successor);
 275                 }
 276
 277                 tmp = node->rb_left;
 278                 WRITE_ONCE(successor->rb_left, tmp);
 279                 rb_set_parent(tmp, successor);
 280
 281                 pc = node->__rb_parent_color;
 282                 tmp = __rb_parent(pc);
 283                 __rb_change_child(node, successor, tmp, root);
 284
 285                 if (child2) {
 286                         rb_set_parent_color(child2, parent, RB_BLACK);
 287                         rebalance = NULL;
 288                 } else {
 289                         rebalance = rb_is_black(successor) ? parent : NULL;
 290                 }
 291                 successor->__rb_parent_color = pc;
 292                 tmp = successor;
 293         }
 294
 295         augment->propagate(tmp, NULL);
 296         return rebalance;
 297 }
 298
 299 static __always_inline void
 300 rb_erase_augmented(struct rb_node *node, struct rb_root *root,
 301                    const struct rb_augment_callbacks *augment)
 302 {
 303         struct rb_node *rebalance = __rb_erase_augmented(node, root, augment);
 304         if (rebalance)
 305                 __rb_erase_color(rebalance, root, augment->rotate);
 306 }
 307
 308 static __always_inline void
 309 rb_erase_augmented_cached(struct rb_node *node, struct rb_root_cached *root,
 310                           const struct rb_augment_callbacks *augment)
 311 {
 312         if (root->rb_leftmost == node)
 313                 root->rb_leftmost = rb_next(node);
 314         rb_erase_augmented(node, &root->rb_root, augment);
 315 }
 316
 317 #endif  /* _LINUX_RBTREE_AUGMENTED_H */