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/*

 * Copyright (C) 2006 Jakub Jermar

 * All rights reserved.

 *

 * Redistribution and use in source and binary forms, with or without

 * modification, are permitted provided that the following conditions

 * are met:

 *

 * - Redistributions of source code must retain the above copyright

 *   notice, this list of conditions and the following disclaimer.

 * - Redistributions in binary form must reproduce the above copyright

 *   notice, this list of conditions and the following disclaimer in the

 *   documentation and/or other materials provided with the distribution.

 * - The name of the author may not be used to endorse or promote products

 *   derived from this software without specific prior written permission.

 *

 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR

 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES

 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.

 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,

 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT

 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,

 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY

 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT

 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF

 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

 */

/*

 * This B-tree has the following properties:

 * - it is a ballanced 2-3-4 tree (i.e. M = 4)

 * - values (i.e. pointers to values) are stored only in leaves

 * - leaves are linked in a list

 * - technically, it is a B+-tree (because of the previous properties)

 *

 * Some of the functions below take pointer to the right-hand

 * side subtree pointer as parameter. Note that this is sufficient

 * because:

 *  - New root node is passed the left-hand side subtree pointer

 *    directly.

 *  - node_split() always creates the right sibling and preserves

 *    the original node (which becomes the left sibling).

 *    There is always pointer to the left-hand side subtree

 *    (i.e. left sibling) in the parent node.

 */

#include <adt/btree.h>

#include <adt/list.h>

#include <mm/slab.h>

#include <debug.h>

#include <panic.h>

#include <typedefs.h>

#include <print.h>

static void _btree_insert(btree_t *t, __native key, void *value, btree_node_t *rsubtree, btree_node_t *node);

static void node_initialize(btree_node_t *node);

static void node_insert_key(btree_node_t *node, __native key, void *value, btree_node_t *rsubtree);

static btree_node_t *node_split(btree_node_t *node, __native key, void *value, btree_node_t *rsubtree, __native *median);

#define ROOT_NODE(n)        (!(n)->parent)

#define INDEX_NODE(n)       ((n)->subtree[0] != NULL)

#define LEAF_NODE(n)        ((n)->subtree[0] == NULL)

#define MEDIAN_LOW_INDEX(n) (((n)->keys-1)/2)

#define MEDIAN_HIGH_INDEX(n)    ((n)->keys/2)

#define MEDIAN_LOW(n)       ((n)->key[MEDIAN_LOW_INDEX((n))]);

#define MEDIAN_HIGH(n)      ((n)->key[MEDIAN_HIGH_INDEX((n))]);

/** Create empty B-tree.

 *

 * @param t B-tree.

 */

void btree_create(btree_t *t)

{

    list_initialize(&t->leaf_head);

    t->root = (btree_node_t *) malloc(sizeof(btree_node_t), 0);

    node_initialize(t->root);

    list_append(&t->root->leaf_link, &t->leaf_head);

}

/** Destroy empty B-tree. */

void btree_destroy(btree_t *t)

{

    ASSERT(!t->root->keys);

    free(t->root);

}

/** Insert key-value pair into B-tree.

 *

 * @param t B-tree.

 * @param key Key to be inserted.

 * @param value Value to be inserted.

 * @param leaf_node Leaf node where the insertion should begin.

 */

void btree_insert(btree_t *t, __native key, void *value, btree_node_t *leaf_node)

{

    btree_node_t *lnode;

    ASSERT(value);

    lnode = leaf_node;

    if (!lnode) {

        if (btree_search(t, key, &lnode)) {

            panic("B-tree %P already contains key %d\n", t, key);

        }

    }

    _btree_insert(t, key, value, NULL, lnode);

}

/** Recursively insert into B-tree.

 *

 * @param t B-tree.

 * @param key Key to be inserted.

 * @param value Value to be inserted.

 * @param rsubtree Right subtree of the inserted key.

 * @param node Start inserting into this node.

 */

void _btree_insert(btree_t *t, __native key, void *value, btree_node_t *rsubtree, btree_node_t *node)

{

    if (node->keys < BTREE_MAX_KEYS) {

        /*

         * Node conatins enough space, the key can be stored immediately.

         */

        node_insert_key(node, key, value, rsubtree);

    } else {

        btree_node_t *rnode;

        __native median;

        /*

         * Node is full.

         * Split it and insert the smallest key from the node containing

         * bigger keys (i.e. the original node) into its parent.

         */

        rnode = node_split(node, key, value, rsubtree, &median);

        if (LEAF_NODE(node)) {

            list_append(&rnode->leaf_link, &node->leaf_link);

        }

        if (ROOT_NODE(node)) {

            /*

             * We split the root node. Create new root.

             */

            t->root = (btree_node_t *) malloc(sizeof(btree_node_t), 0);

            node->parent = t->root;

            rnode->parent = t->root;

            node_initialize(t->root);

            /*

             * Left-hand side subtree will be the old root (i.e. node).

             * Right-hand side subtree will be rnode.

             */        

            t->root->subtree[0] = node;

            t->root->depth = node->depth + 1;

        }

        _btree_insert(t, median, NULL, rnode, node->parent);

    }  

}

/* TODO */

void btree_remove(btree_t *t, __native key)

{

}

/** Search key in a B-tree.

 *

 * @param t B-tree.

 * @param key Key to be searched.

 * @param leaf_node Address where to put pointer to visited leaf node.

 *

 * @return Pointer to value or NULL if there is no such key.

 */

void *btree_search(btree_t *t, __native key, btree_node_t **leaf_node)

{

    btree_node_t *cur, *next;

    void *val = NULL;

    /*

     * Iteratively descend to the leaf that can contain searched key.

     */

    for (cur = t->root; cur; cur = next) {

        int i;

        /* Last iteration will set this with proper leaf node address. */

        *leaf_node = cur;

        for (i = 0; i < cur->keys; i++) {

            if (key <= cur->key[i]) {

                val = cur->value[i];

                next = cur->subtree[i];

                /*

                 * Check if there is anywhere to descend.

                 */

                if (!next) {

                    /*

                     * Leaf-level.

                     */

                    return (key == cur->key[i]) ? val : NULL;

                }

                goto descend;

            }

        }

        next = cur->subtree[i];

    descend:

        ;

    }

    /*

     * The key was not found in the *leaf_node and is greater than any of its keys.

     */

    return NULL;

}

/** Get pointer to value with the smallest key within the node.

 *

 * Can be only used on leaf-level nodes.

 *

 * @param node B-tree node.

 *

 * @return Pointer to value assiciated with the smallest key.

 */

void *btree_node_min(btree_node_t *node)

{

    ASSERT(LEAF_NODE(node));

    ASSERT(node->keys);

    return node->value[0];

}

/** Get pointer to value with the biggest key within the node.

 *

 * Can be only used on leaf-level nodes.

 *

 * @param node B-tree node.

 *

 * @return Pointer to value assiciated with the biggest key.

 */

void *btree_node_max(btree_node_t *node)

{

    ASSERT(LEAF_NODE(node));

    ASSERT(node->keys);

    return node->value[node->keys - 1];

}

/** Initialize B-tree node.

 *

 * @param node B-tree node.

 */

void node_initialize(btree_node_t *node)

{

    int i;

    node->keys = 0;

    /* Clean also space for the extra key. */

    for (i = 0; i < BTREE_MAX_KEYS + 1; i++) {

        node->key[i] = 0;

        node->value[i] = NULL;

        node->subtree[i] = NULL;

    }

    node->subtree[i] = NULL;

    node->parent = NULL;

    link_initialize(&node->leaf_link);

    link_initialize(&node->bfs_link);

    node->depth = 0;

}

/** Insert key-value-left-subtree triplet into B-tree non-full node.

 *

 * It is actually possible to have more keys than BTREE_MAX_KEYS.

 * This feature is used during splitting the node when the

 * number of keys is BTREE_MAX_KEYS + 1.

 *

 * @param node B-tree node into wich the new key is to be inserted.

 * @param key The key to be inserted.

 * @param value Pointer to value to be inserted.

 * @param rsubtree Pointer to the right subtree.

 */

void node_insert_key(btree_node_t *node, __native key, void *value, btree_node_t *rsubtree)

{

    int i;

    for (i = 0; i < node->keys; i++) {

        if (key < node->key[i]) {

            int j;

            for (j = node->keys; j > i; j--) {

                node->key[j] = node->key[j - 1];

                node->value[j] = node->value[j - 1];

                node->subtree[j + 1] = node->subtree[j];

            }

            break; 

        }

    }

    node->key[i] = key;

    node->value[i] = value;

    node->subtree[i + 1] = rsubtree;

    node->keys++;

}

/** Split full B-tree node and insert new key-value-left-subtree triplet.

 *

 * This function will split a node and return pointer to a newly created

 * node containing keys greater than the lesser of medians (or median)

 * of the old keys and the newly added key. It will also write the

 * median key to a memory address supplied by the caller.

 *

 * If the node being split is an index node, the median will be

 * removed from the original node. If the node is a leaf node,

 * the median will be preserved.

 *

 * @param node B-tree node wich is going to be split.

 * @param key The key to be inserted.

 * @param value Pointer to the value to be inserted.

 * @param rsubtree Pointer to the right subtree of the key being added.

 * @param median Address in memory, where the median key will be stored.

 *

 * @return Newly created right sibling of node.

 */

btree_node_t *node_split(btree_node_t *node, __native key, void *value, btree_node_t *rsubtree, __native *median)

{

    btree_node_t *rnode;

    int i, j;

    ASSERT(median);

    ASSERT(node->keys == BTREE_MAX_KEYS);

    /*

     * Use the extra space to store the extra node.

     */

    node_insert_key(node, key, value, rsubtree);

    /*

     * Compute median of keys.

     */

    *median = MEDIAN_LOW(node);

    rnode = (btree_node_t *) malloc(sizeof(btree_node_t), 0);

    node_initialize(rnode);

    rnode->parent = node->parent;

    rnode->depth = node->depth;

    /*

     * Copy big keys, values and subtree pointers to the new right sibling.

     */

    for (i = MEDIAN_LOW_INDEX(node) + 1, j = 0; i < node->keys; i++, j++) {

        rnode->key[j] = node->key[i];

        rnode->value[j] = node->value[i];

        rnode->subtree[j] = node->subtree[i];

        /*

         * Fix parent links in subtrees.

         */

        if (rnode->subtree[j])

            rnode->subtree[j]->parent = rnode;

    }

    rnode->subtree[j] = node->subtree[i];

    if (rnode->subtree[j])

        rnode->subtree[j]->parent = rnode;

    rnode->keys = j;

    /*

     * Shrink the old node.

     * If this is an index node, remove the median.

     */

    node->keys = MEDIAN_LOW_INDEX(node) + 1;

    if (INDEX_NODE(node))

        node->keys--;

    return rnode;

}

/** Print B-tree.

 *

 * @param t Print out B-tree.

 */

void btree_print(btree_t *t)

{

    int i, depth = t->root->depth;

    link_t head;

    list_initialize(&head);

    list_append(&t->root->bfs_link, &head);

    /*

     * Use BFS search to print out the tree.

     * Levels are distinguished from one another by node->depth.

     */

    while (!list_empty(&head)) {

        link_t *hlp;

        btree_node_t *node;

        hlp = head.next;

        ASSERT(hlp != &head);

        node = list_get_instance(hlp, btree_node_t, bfs_link);

        list_remove(hlp);

        ASSERT(node);

        if (node->depth != depth) {

            printf("\n");

            depth = node->depth;

        }

        printf("(");

        for (i = 0; i < node->keys; i++) {

            printf("%d,", node->key[i]);

            if (node->depth && node->subtree[i]) {

                list_append(&node->subtree[i]->bfs_link, &head);

            }

        }

        if (node->depth && node->subtree[i]) {

            list_append(&node->subtree[i]->bfs_link, &head);

        }

        printf(")");

    }

    printf("\n");

}