rbtree_augmented.h

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/* SPDX-License-Identifier: GPL-2.0-or-later */
/*
  Red Black Trees
  (C) 1999  Andrea Arcangeli <andrea@suse.de>
  (C) 2002  David Woodhouse <dwmw2@infradead.org>
  (C) 2012  Michel Lespinasse <walken@google.com>
 
 
  linux/include/linux/rbtree_augmented.h
*/
 
#ifndef _LINUX_RBTREE_AUGMENTED_H
#define _LINUX_RBTREE_AUGMENTED_H
 
#include <linux/compiler.h>
#include <linux/rbtree.h>
#include <linux/rcupdate.h>
 
/*
 * Please note - only struct rb_augment_callbacks and the prototypes for
 * rb_insert_augmented() and rb_erase_augmented() are intended to be public.
 * The rest are implementation details you are not expected to depend on.
 *
 * See Documentation/core-api/rbtree.rst for documentation and samples.
 */
 
struct rb_augment_callbacks {
    void (*propagate)(struct rb_node *node, struct rb_node *stop);
    void (*copy)(struct rb_node *old, struct rb_node *new);
    void (*rotate)(struct rb_node *old, struct rb_node *new);
};
 
extern void __rb_insert_augmented(struct rb_node *node, struct rb_root *root,
    void (*augment_rotate)(struct rb_node *old, struct rb_node *new));
 
/*
 * Fixup the rbtree and update the augmented information when rebalancing.
 *
 * On insertion, the user must update the augmented information on the path
 * leading to the inserted node, then call rb_link_node() as usual and
 * rb_insert_augmented() instead of the usual rb_insert_color() call.
 * If rb_insert_augmented() rebalances the rbtree, it will callback into
 * a user provided function to update the augmented information on the
 * affected subtrees.
 */
static inline void
rb_insert_augmented(struct rb_node *node, struct rb_root *root,
            const struct rb_augment_callbacks *augment)
{
    __rb_insert_augmented(node, root, augment->rotate);
}
 
static inline void
rb_insert_augmented_cached(struct rb_node *node,
               struct rb_root_cached *root, bool newleft,
               const struct rb_augment_callbacks *augment)
{
    if (newleft)
        root->rb_leftmost = node;
    rb_insert_augmented(node, &root->rb_root, augment);
}
 
static __always_inline struct rb_node *
rb_add_augmented_cached(struct rb_node *node, struct rb_root_cached *tree,
            bool (*less)(struct rb_node *, const struct rb_node *),
            const struct rb_augment_callbacks *augment)
{
    struct rb_node **link = &tree->rb_root.rb_node;
    struct rb_node *parent = NULL;
    bool leftmost = true;
 
    while (*link) {
        parent = *link;
        if (less(node, parent)) {
            link = &parent->rb_left;
        } else {
            link = &parent->rb_right;
            leftmost = false;
        }
    }
 
    rb_link_node(node, parent, link);
    augment->propagate(parent, NULL); /* suboptimal */
    rb_insert_augmented_cached(node, tree, leftmost, augment);
 
    return leftmost ? node : NULL;
}
 
/*
 * Template for declaring augmented rbtree callbacks (generic case)
 *
 * RBSTATIC:    'static' or empty
 * RBNAME:      name of the rb_augment_callbacks structure
 * RBSTRUCT:    struct type of the tree nodes
 * RBFIELD:     name of struct rb_node field within RBSTRUCT
 * RBAUGMENTED: name of field within RBSTRUCT holding data for subtree
 * RBCOMPUTE:   name of function that recomputes the RBAUGMENTED data
 */
 
#define RB_DECLARE_CALLBACKS(RBSTATIC, RBNAME,              \
                 RBSTRUCT, RBFIELD, RBAUGMENTED, RBCOMPUTE) \
static inline void                          \
RBNAME ## _propagate(struct rb_node *rb, struct rb_node *stop)      \
{                                   \
    while (rb != stop) {                        \
        RBSTRUCT *node = rb_entry(rb, RBSTRUCT, RBFIELD);   \
        if (RBCOMPUTE(node, true))              \
            break;                      \
        rb = rb_parent(&node->RBFIELD);             \
    }                               \
}                                   \
static inline void                          \
RBNAME ## _copy(struct rb_node *rb_old, struct rb_node *rb_new)     \
{                                   \
    RBSTRUCT *old = rb_entry(rb_old, RBSTRUCT, RBFIELD);        \
    RBSTRUCT *new = rb_entry(rb_new, RBSTRUCT, RBFIELD);        \
    new->RBAUGMENTED = old->RBAUGMENTED;                \
}                                   \
static void                             \
RBNAME ## _rotate(struct rb_node *rb_old, struct rb_node *rb_new)   \
{                                   \
    RBSTRUCT *old = rb_entry(rb_old, RBSTRUCT, RBFIELD);        \
    RBSTRUCT *new = rb_entry(rb_new, RBSTRUCT, RBFIELD);        \
    new->RBAUGMENTED = old->RBAUGMENTED;                \
    RBCOMPUTE(old, false);                      \
}                                   \
RBSTATIC const struct rb_augment_callbacks RBNAME = {           \
    .propagate = RBNAME ## _propagate,              \
    .copy = RBNAME ## _copy,                    \
    .rotate = RBNAME ## _rotate                 \
};
 
/*
 * Template for declaring augmented rbtree callbacks,
 * computing RBAUGMENTED scalar as max(RBCOMPUTE(node)) for all subtree nodes.
 *
 * RBSTATIC:    'static' or empty
 * RBNAME:      name of the rb_augment_callbacks structure
 * RBSTRUCT:    struct type of the tree nodes
 * RBFIELD:     name of struct rb_node field within RBSTRUCT
 * RBTYPE:      type of the RBAUGMENTED field
 * RBAUGMENTED: name of RBTYPE field within RBSTRUCT holding data for subtree
 * RBCOMPUTE:   name of function that returns the per-node RBTYPE scalar
 */
 
#define RB_DECLARE_CALLBACKS_MAX(RBSTATIC, RBNAME, RBSTRUCT, RBFIELD,         \
                 RBTYPE, RBAUGMENTED, RBCOMPUTE)          \
static inline bool RBNAME ## _compute_max(RBSTRUCT *node, bool exit)          \
{                                         \
    RBSTRUCT *child;                              \
    RBTYPE max = RBCOMPUTE(node);                         \
    if (node->RBFIELD.rb_left) {                          \
        child = rb_entry(node->RBFIELD.rb_left, RBSTRUCT, RBFIELD);   \
        if (child->RBAUGMENTED > max)                     \
            max = child->RBAUGMENTED;                 \
    }                                     \
    if (node->RBFIELD.rb_right) {                         \
        child = rb_entry(node->RBFIELD.rb_right, RBSTRUCT, RBFIELD);  \
        if (child->RBAUGMENTED > max)                     \
            max = child->RBAUGMENTED;                 \
    }                                     \
    if (exit && node->RBAUGMENTED == max)                     \
        return true;                              \
    node->RBAUGMENTED = max;                          \
    return false;                                 \
}                                         \
RB_DECLARE_CALLBACKS(RBSTATIC, RBNAME,                        \
             RBSTRUCT, RBFIELD, RBAUGMENTED, RBNAME ## _compute_max)
 
 
#define RB_RED      0
#define RB_BLACK    1
 
#define __rb_parent(pc)    ((struct rb_node *)(pc & ~3))
 
#define __rb_color(pc)     ((pc) & 1)
#define __rb_is_black(pc)  __rb_color(pc)
#define __rb_is_red(pc)    (!__rb_color(pc))
#define rb_color(rb)       __rb_color((rb)->__rb_parent_color)
#define rb_is_red(rb)      __rb_is_red((rb)->__rb_parent_color)
#define rb_is_black(rb)    __rb_is_black((rb)->__rb_parent_color)
 
/* DCL delta -- `uintptr_t`; see rbtree.h. */
static inline void rb_set_parent(struct rb_node *rb, struct rb_node *p)
{
    rb->__rb_parent_color = rb_color(rb) + (uintptr_t)p;
}
 
/* DCL delta -- `uintptr_t`; see rbtree.h. */
static inline void rb_set_parent_color(struct rb_node *rb,
                       struct rb_node *p, int color)
{
    rb->__rb_parent_color = (uintptr_t)p + color;
}
 
static inline void
__rb_change_child(struct rb_node *old, struct rb_node *new,
          struct rb_node *parent, struct rb_root *root)
{
    if (parent) {
        if (parent->rb_left == old)
            WRITE_ONCE(parent->rb_left, new);
        else
            WRITE_ONCE(parent->rb_right, new);
    } else
        WRITE_ONCE(root->rb_node, new);
}
 
static inline void
__rb_change_child_rcu(struct rb_node *old, struct rb_node *new,
              struct rb_node *parent, struct rb_root *root)
{
    if (parent) {
        if (parent->rb_left == old)
            rcu_assign_pointer(parent->rb_left, new);
        else
            rcu_assign_pointer(parent->rb_right, new);
    } else
        rcu_assign_pointer(root->rb_node, new);
}
 
extern void __rb_erase_color(struct rb_node *parent, struct rb_root *root,
    void (*augment_rotate)(struct rb_node *old, struct rb_node *new));
 
static __always_inline struct rb_node *
__rb_erase_augmented(struct rb_node *node, struct rb_root *root,
             const struct rb_augment_callbacks *augment)
{
    struct rb_node *child = node->rb_right;
    struct rb_node *tmp = node->rb_left;
    struct rb_node *parent, *rebalance;
    /*
     * DCL delta -- `uintptr_t`; see rbtree.h.  `pc` holds a whole
     * __rb_parent_color (parent pointer plus color bit) and is written
     * back into nodes below, so it cannot be a 32-bit `unsigned long`
     * here.
     */
    uintptr_t pc;
 
    if (!tmp) {
        /*
         * Case 1: node to erase has no more than 1 child (easy!)
         *
         * Note that if there is one child it must be red due to 5)
         * and node must be black due to 4). We adjust colors locally
         * so as to bypass __rb_erase_color() later on.
         */
        pc = node->__rb_parent_color;
        parent = __rb_parent(pc);
        __rb_change_child(node, child, parent, root);
        if (child) {
            child->__rb_parent_color = pc;
            rebalance = NULL;
        } else
            rebalance = __rb_is_black(pc) ? parent : NULL;
        tmp = parent;
    } else if (!child) {
        /* Still case 1, but this time the child is node->rb_left */
        tmp->__rb_parent_color = pc = node->__rb_parent_color;
        parent = __rb_parent(pc);
        __rb_change_child(node, tmp, parent, root);
        rebalance = NULL;
        tmp = parent;
    } else {
        struct rb_node *successor = child, *child2;
 
        tmp = child->rb_left;
        if (!tmp) {
            /*
             * Case 2: node's successor is its right child
             *
             *    (n)          (s)
             *    / \          / \
             *  (x) (s)  ->  (x) (c)
             *        \
             *        (c)
             */
            parent = successor;
            child2 = successor->rb_right;
 
            augment->copy(node, successor);
        } else {
            /*
             * Case 3: node's successor is leftmost under
             * node's right child subtree
             *
             *    (n)          (s)
             *    / \          / \
             *  (x) (y)  ->  (x) (y)
             *      /            /
             *    (p)          (p)
             *    /            /
             *  (s)          (c)
             *    \
             *    (c)
             */
            do {
                parent = successor;
                successor = tmp;
                tmp = tmp->rb_left;
            } while (tmp);
            child2 = successor->rb_right;
            WRITE_ONCE(parent->rb_left, child2);
            WRITE_ONCE(successor->rb_right, child);
            rb_set_parent(child, successor);
 
            augment->copy(node, successor);
            augment->propagate(parent, successor);
        }
 
        tmp = node->rb_left;
        WRITE_ONCE(successor->rb_left, tmp);
        rb_set_parent(tmp, successor);
 
        pc = node->__rb_parent_color;
        tmp = __rb_parent(pc);
        __rb_change_child(node, successor, tmp, root);
 
        if (child2) {
            rb_set_parent_color(child2, parent, RB_BLACK);
            rebalance = NULL;
        } else {
            rebalance = rb_is_black(successor) ? parent : NULL;
        }
        successor->__rb_parent_color = pc;
        tmp = successor;
    }
 
    augment->propagate(tmp, NULL);
    return rebalance;
}
 
static __always_inline void
rb_erase_augmented(struct rb_node *node, struct rb_root *root,
           const struct rb_augment_callbacks *augment)
{
    struct rb_node *rebalance = __rb_erase_augmented(node, root, augment);
    if (rebalance)
        __rb_erase_color(rebalance, root, augment->rotate);
}
 
static __always_inline void
rb_erase_augmented_cached(struct rb_node *node, struct rb_root_cached *root,
              const struct rb_augment_callbacks *augment)
{
    if (root->rb_leftmost == node)
        root->rb_leftmost = rb_next(node);
    rb_erase_augmented(node, &root->rb_root, augment);
}
 
#endif  /* _LINUX_RBTREE_AUGMENTED_H */