/*
 * Copyright (c) 2010-2017 Richard Braun.
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 *
 * Upstream site with license notes :
 * http://git.sceen.net/rbraun/librbraun.git/
 */

#ifndef KERN_RBTREE_I_H
#define KERN_RBTREE_I_H

#include <assert.h>
#include <stddef.h>
#include <stdint.h>

#include <kern/macros.h>

/*
 * Red-black node structure.
 *
 * To reduce the number of branches and the instruction cache footprint,
 * the left and right child pointers are stored in an array, and the symmetry
 * of most tree operations is exploited by using left/right variables when
 * referring to children.
 *
 * In addition, this implementation assumes that all nodes are 4-byte aligned,
 * so that the least significant bit of the parent member can be used to store
 * the color of the node. This is true for all modern 32 and 64 bits
 * architectures, as long as the nodes aren't embedded in structures with
 * special alignment constraints such as member packing.
 */
struct rbtree_node {
    uintptr_t parent;
    struct rbtree_node *children[2];
};

/*
 * Red-black tree structure.
 */
struct rbtree {
    struct rbtree_node *root;
};

/*
 * Masks applied on the parent member of a node to obtain either the
 * color or the parent address.
 */
#define RBTREE_COLOR_MASK   ((uintptr_t)0x1)
#define RBTREE_PARENT_MASK  (~(uintptr_t)0x3)

/*
 * Node colors.
 */
#define RBTREE_COLOR_RED    0
#define RBTREE_COLOR_BLACK  1

/*
 * Masks applied on slots to obtain either the child index or the parent
 * address.
 */
#define RBTREE_SLOT_INDEX_MASK  0x1UL
#define RBTREE_SLOT_PARENT_MASK (~RBTREE_SLOT_INDEX_MASK)

/*
 * Return true if the given index is a valid child index.
 */
static inline int
rbtree_check_index(int index)
{
    return index == (index & 1);
}

/*
 * Convert the result of a comparison into an index in the children array
 * (0 or 1).
 *
 * This function is mostly used when looking up a node.
 */
static inline int
rbtree_d2i(int diff)
{
    return !(diff <= 0);
}

/*
 * Return true if the given pointer is suitably aligned.
 */
static inline int
rbtree_node_check_alignment(const struct rbtree_node *node)
{
    return ((uintptr_t)node & (~RBTREE_PARENT_MASK)) == 0;
}

/*
 * Return the parent of a node.
 */
static inline struct rbtree_node *
rbtree_node_parent(const struct rbtree_node *node)
{
    return (struct rbtree_node *)(node->parent & RBTREE_PARENT_MASK);
}

/*
 * Translate an insertion point into a slot.
 */
static inline rbtree_slot_t
rbtree_slot(struct rbtree_node *parent, int index)
{
    assert(rbtree_node_check_alignment(parent));
    assert(rbtree_check_index(index));
    return (rbtree_slot_t)parent | index;
}

/*
 * Extract the parent address from a slot.
 */
static inline struct rbtree_node *
rbtree_slot_parent(rbtree_slot_t slot)
{
    return (struct rbtree_node *)(slot & RBTREE_SLOT_PARENT_MASK);
}

/*
 * Extract the index from a slot.
 */
static inline int
rbtree_slot_index(rbtree_slot_t slot)
{
    return slot & RBTREE_SLOT_INDEX_MASK;
}

/*
 * Insert a node in a tree, rebalancing it if necessary.
 *
 * The index parameter is the index in the children array of the parent where
 * the new node is to be inserted. It is ignored if the parent is NULL.
 *
 * This function is intended to be used by the rbtree_insert() macro only.
 */
void rbtree_insert_rebalance(struct rbtree *tree, struct rbtree_node *parent,
                             int index, struct rbtree_node *node);

/*
 * Return the previous or next node relative to a location in a tree.
 *
 * The parent and index parameters define the location, which can be empty.
 * The direction parameter is either RBTREE_LEFT (to obtain the previous
 * node) or RBTREE_RIGHT (to obtain the next one).
 */
struct rbtree_node * rbtree_nearest(struct rbtree_node *parent, int index,
                                    int direction);

/*
 * Return the first or last node of a tree.
 *
 * The direction parameter is either RBTREE_LEFT (to obtain the first node)
 * or RBTREE_RIGHT (to obtain the last one).
 */
struct rbtree_node * rbtree_firstlast(const struct rbtree *tree, int direction);

/*
 * Return the node next to, or previous to the given node.
 *
 * The direction parameter is either RBTREE_LEFT (to obtain the previous node)
 * or RBTREE_RIGHT (to obtain the next one).
 */
struct rbtree_node * rbtree_walk(struct rbtree_node *node, int direction);

/*
 * Return the left-most deepest node of a tree, which is the starting point of
 * the postorder traversal performed by rbtree_for_each_remove().
 */
struct rbtree_node * rbtree_postwalk_deepest(const struct rbtree *tree);

/*
 * Unlink a node from its tree and return the next (right) node in postorder.
 */
struct rbtree_node * rbtree_postwalk_unlink(struct rbtree_node *node);

#endif /* KERN_RBTREE_I_H */