source: mainline/generic/src/adt/btree.c@ 50fe620

/*
 * 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. BTREE_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)
 *
 * Be carefull when using these trees. They need to allocate
 * and deallocate memory for their index nodes and as such
 * can sleep.
 */

#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_left(btree_node_t *node, __native key, void *value, btree_node_t *rsubtree);
static void node_insert_key_right(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);
static void node_remove_key_left(btree_node_t *node, __native key);
static void node_remove_key_right(btree_node_t *node, __native key);
static index_t find_key_by_subtree(btree_node_t *node, btree_node_t *subtree, bool right);
static bool try_insert_by_left_rotation(btree_node_t *node, __native key, void *value, btree_node_t *rsubtree);
static bool try_insert_by_right_rotation(btree_node_t *node, __native key, void *value, btree_node_t *rsubtree);

#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_right(node, key, value, rsubtree);
        } else if (try_insert_by_left_rotation(node, key, value, rsubtree)) {
                /*
                 * The key-value-rsubtree triplet has been inserted because
                 * some keys could have been moved to the left sibling.
                 */
        } else if (try_insert_by_right_rotation(node, key, value, rsubtree)) {
                /*
                 * The key-value-rsubtree triplet has been inserted because
                 * some keys could have been moved to the right sibling.
                 */
        } else {
                btree_node_t *rnode;
                __native median;
                
                /*
                 * Node is full and both siblings (if both exist) are full too.
                 * Split the node and insert the smallest key from the node containing
                 * bigger keys (i.e. the new 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;
        
        /*
         * Iteratively descend to the leaf that can contain the searched key.
         */
        for (cur = t->root; cur; cur = next) {

                /* Last iteration will set this with proper leaf node address. */
                *leaf_node = cur;
                
                /*
                 * The key can be in the leftmost subtree.
                 * Test it separately.
                 */
                if (key < cur->key[0]) {
                        next = cur->subtree[0];
                        continue;
                } else {
                        void *val;
                        int i;
                
                        /*
                         * Now if the key is smaller than cur->key[i]
                         * it can only mean that the value is in cur->subtree[i]
                         * or it is not in the tree at all.
                         */
                        for (i = 1; i < cur->keys; i++) {
                                if (key < cur->key[i]) {
                                        next = cur->subtree[i];
                                        val = cur->value[i - 1];

                                        if (LEAF_NODE(cur))
                                                return key == cur->key[i - 1] ? val : NULL;

                                        goto descend;
                                } 
                        }
                        
                        /*
                         * Last possibility is that the key is in the rightmost subtree.
                         */
                        next = cur->subtree[i];
                        val = cur->value[i - 1];
                        if (LEAF_NODE(cur))
                                return key == cur->key[i - 1] ? val : NULL;
                }
                descend:
                        ;
        }

        /*
         * The key was not found in the *leaf_node and is smaller 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-lsubtree triplet into B-tree node.
 *
 * It is actually possible to have more keys than BTREE_MAX_KEYS.
 * This feature is used during insert by right rotation.
 *
 * @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 lsubtree Pointer to the left subtree.
 */ 
void node_insert_key_left(btree_node_t *node, __native key, void *value, btree_node_t *lsubtree)
{
        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];
                        }
                        node->subtree[j + 1] = node->subtree[j];
                        break;  
                }
        }
        node->key[i] = key;
        node->value[i] = value;
        node->subtree[i] = lsubtree;
                        
        node->keys++;
}


/** Insert key-value-rsubtree triplet into B-tree 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. Insert by left rotation
 * also makes use of this feature.
 *
 * @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_right(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-right-subtree triplet.
 *
 * This function will split a node and return pointer to a newly created
 * node containing keys greater than or equal to the greater 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 not be
 * included in the new node. If the node is a leaf node,
 * the median will be copied there.
 *
 * @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_right(node, key, value, rsubtree);

        /*
         * Compute median of keys.
         */
        *median = MEDIAN_HIGH(node);
                
        /*
         * Allocate and initialize new right sibling.
         */
        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.
         * If this is an index node, do not copy the median.
         */
        i = (int) INDEX_NODE(node);
        for (i += MEDIAN_HIGH_INDEX(node), 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;        /* Set number of keys of the new node. */
        node->keys /= 2;        /* Shrink the old node. */
                
        return rnode;
}

/** Remove key and its left subtree pointer from B-tree node.
 *
 * Remove the key and eliminate gaps in node->key array.
 * Note that the value pointer and the left subtree pointer
 * is removed from the node as well.
 *
 * @param node B-tree node.
 * @param key Key to be removed.
 */
void node_remove_key_left(btree_node_t *node, __native key)
{
        int i, j;
        
        for (i = 0; i < node->keys; i++) {
                if (key == node->key[i]) {
                        for (j = i + 1; j < node->keys; j++) {
                                node->key[j - 1] = node->key[j];
                                node->value[j - 1] = node->value[j];
                                node->subtree[j - 1] = node->subtree[j];
                        }
                        node->subtree[j - 1] = node->subtree[j];
                        node->keys--;
                        return;
                }
        }
        panic("node %P does not contain key %d\n", node, key);
}

/** Remove key and its right subtree pointer from B-tree node.
 *
 * Remove the key and eliminate gaps in node->key array.
 * Note that the value pointer and the right subtree pointer
 * is removed from the node as well.
 *
 * @param node B-tree node.
 * @param key Key to be removed.
 */
void node_remove_key_right(btree_node_t *node, __native key)
{
        int i, j;
        
        for (i = 0; i < node->keys; i++) {
                if (key == node->key[i]) {
                        for (j = i + 1; j < node->keys; j++) {
                                node->key[j - 1] = node->key[j];
                                node->value[j - 1] = node->value[j];
                                node->subtree[j] = node->subtree[j + 1];
                        }
                        node->keys--;
                        return;
                }
        }
        panic("node %P does not contain key %d\n", node, key);
}

/** Find key by its left or right subtree.
 *
 * @param node B-tree node.
 * @param subtree Left or right subtree of a key found in node.
 * @param right If true, subtree is a right subtree. If false, subtree is a left subtree.
 *
 * @return Index of the key associated with the subtree.
 */ 
index_t find_key_by_subtree(btree_node_t *node, btree_node_t *subtree, bool right)
{
        int i;
        
        for (i = 0; i < node->keys + 1; i++) {
                if (subtree == node->subtree[i])
                        return i - (int) (right != false);
        }
        panic("node %P does not contain subtree %P\n", node, subtree);
}

/** Insert key-value-rsubtree triplet and rotate the node to the left, if this operation can be done.
 *
 * Left sibling of the node (if it exists) is checked for free space.
 * If there is free space, the key is inserted and the smallest key of
 * the node is moved there. The index node which is the parent of both
 * nodes is fixed.
 *
 * @param node B-tree node.
 * @param inskey Key to be inserted.
 * @param insvalue Value to be inserted.
 * @param rsubtree Right subtree of inskey.
 *
 * @return True if the rotation was performed, false otherwise.
 */
bool try_insert_by_left_rotation(btree_node_t *node, __native inskey, void *insvalue, btree_node_t *rsubtree)
{
        index_t idx;
        btree_node_t *lnode;

        /*
         * If this is root node, the rotation can not be done.
         */
        if (ROOT_NODE(node))
                return false;
        
        idx = find_key_by_subtree(node->parent, node, true);
        if ((int) idx == -1) {
                /*
                 * If this node is the leftmost subtree of its parent,
                 * the rotation can not be done.
                 */
                return false;
        }
                
        lnode = node->parent->subtree[idx];

        if (lnode->keys < BTREE_MAX_KEYS) {
                __native key;

                /*
                 * The rotaion can be done. The left sibling has free space.
                 */

                node_insert_key_right(node, inskey, insvalue, rsubtree);
                key = node->key[0];
                
                if (LEAF_NODE(node)) {
                        void *value;

                        value = node->value[0];
                        node_remove_key_left(node, key);
                        node_insert_key_right(lnode, key, value, NULL);
                        node->parent->key[idx] = node->key[0];
                } else {
                        btree_node_t *lsubtree;

                        lsubtree = node->subtree[0];
                        node_remove_key_left(node, key);
                        node_insert_key_right(lnode, node->parent->key[idx], NULL, lsubtree);
                        node->parent->key[idx] = key;

                        /* Fix parent link of the reconnected left subtree. */
                        lsubtree->parent = lnode;
                }
                return true;
        }

        return false;
}

/** Insert key-value-rsubtree triplet and rotate the node to the right, if this operation can be done.
 *
 * Right sibling of the node (if it exists) is checked for free space.
 * If there is free space, the key is inserted and the biggest key of
 * the node is moved there. The index node which is the parent of both
 * nodes is fixed.
 *
 * @param node B-tree node.
 * @param inskey Key to be inserted.
 * @param insvalue Value to be inserted.
 * @param rsubtree Right subtree of inskey.
 *
 * @return True if the rotation was performed, false otherwise.
 */
bool try_insert_by_right_rotation(btree_node_t *node, __native inskey, void *insvalue, btree_node_t *rsubtree)
{
        index_t idx;
        btree_node_t *rnode;

        /*
         * If this is root node, the rotation can not be done.
         */
        if (ROOT_NODE(node))
                return false;
        
        idx = find_key_by_subtree(node->parent, node, false);
        if (idx == node->parent->keys) {
                /*
                 * If this node is the rightmost subtree of its parent,
                 * the rotation can not be done.
                 */
                return false;
        }
                
        rnode = node->parent->subtree[idx + 1];

        if (rnode->keys < BTREE_MAX_KEYS) {
                __native key;

                /*
                 * The rotaion can be done. The right sibling has free space.
                 */

                node_insert_key_right(node, inskey, insvalue, rsubtree);
                key = node->key[node->keys - 1];
                
                if (LEAF_NODE(node)) {
                        void *value;

                        value = node->value[node->keys - 1];
                        node_remove_key_right(node, key);
                        node_insert_key_left(rnode, key, value, NULL);
                        node->parent->key[idx] = key;
                } else {
                        btree_node_t *rsubt;

                        rsubt = node->subtree[node->keys];
                        node_remove_key_right(node, key);
                        node_insert_key_left(rnode, node->parent->key[idx], NULL, rsubt);
                        node->parent->key[idx] = key;

                        /* Fix parent link of the reconnected right subtree. */
                        rsubt->parent = rnode;
                }
                return true;
        }

        return false;
}

/** 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");
}