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 static __always_inline struct rb_node *
  64 rb_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) \
 102 static inline void                                                      \
 103 RBNAME ## _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 }                                                                       \
 112 static inline void                                                      \
 113 RBNAME ## _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 }                                                                       \
 119 static void                                                             \
 120 RBNAME ## _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 }                                                                       \
 127 RBSTATIC 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)              \
 148 static 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 }                                                                             \
 167 RB_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
 183 static 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
 188 static 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
 194 static 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
 207 static 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
 220 extern 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
 223 static __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
 325 static __always_inline void
 326 rb_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
 334 static __always_inline void
 335 rb_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 */