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author | John Birrell <jb@FreeBSD.org> | 2008-04-25 23:33:18 +0000 |
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committer | John Birrell <jb@FreeBSD.org> | 2008-04-25 23:33:18 +0000 |

commit | d876124d6ae9d56da5b4ff4c6015efd1d0c9222a (patch) | |

tree | e6cfdef2a8b9488b25517d80411d703ccb765e26 /cddl/contrib/opensolaris/common/avl | |

parent | 2056b4037cdba1def880066fab7cca98df5b4d86 (diff) | |

parent | 2de84d2572206157cf33d1fb75463eeb42ae8e42 (diff) | |

download | src-d876124d6ae9d56da5b4ff4c6015efd1d0c9222a.tar.gz src-d876124d6ae9d56da5b4ff4c6015efd1d0c9222a.zip |

This commit was generated by cvs2svn to compensate for changes in r178525,

which included commits to RCS files with non-trunk default branches.

Notes

Notes:
svn path=/head/; revision=178526

Diffstat (limited to 'cddl/contrib/opensolaris/common/avl')

-rw-r--r-- | cddl/contrib/opensolaris/common/avl/avl.c | 969 |

1 files changed, 969 insertions, 0 deletions

diff --git a/cddl/contrib/opensolaris/common/avl/avl.c b/cddl/contrib/opensolaris/common/avl/avl.c new file mode 100644 index 000000000000..7403e813014c --- /dev/null +++ b/cddl/contrib/opensolaris/common/avl/avl.c @@ -0,0 +1,969 @@ +/* + * CDDL HEADER START + * + * The contents of this file are subject to the terms of the + * Common Development and Distribution License (the "License"). + * You may not use this file except in compliance with the License. + * + * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE + * or http://www.opensolaris.org/os/licensing. + * See the License for the specific language governing permissions + * and limitations under the License. + * + * When distributing Covered Code, include this CDDL HEADER in each + * file and include the License file at usr/src/OPENSOLARIS.LICENSE. + * If applicable, add the following below this CDDL HEADER, with the + * fields enclosed by brackets "[]" replaced with your own identifying + * information: Portions Copyright [yyyy] [name of copyright owner] + * + * CDDL HEADER END + */ +/* + * Copyright 2006 Sun Microsystems, Inc. All rights reserved. + * Use is subject to license terms. + */ + +#pragma ident "%Z%%M% %I% %E% SMI" + + +/* + * AVL - generic AVL tree implementation for kernel use + * + * A complete description of AVL trees can be found in many CS textbooks. + * + * Here is a very brief overview. An AVL tree is a binary search tree that is + * almost perfectly balanced. By "almost" perfectly balanced, we mean that at + * any given node, the left and right subtrees are allowed to differ in height + * by at most 1 level. + * + * This relaxation from a perfectly balanced binary tree allows doing + * insertion and deletion relatively efficiently. Searching the tree is + * still a fast operation, roughly O(log(N)). + * + * The key to insertion and deletion is a set of tree maniuplations called + * rotations, which bring unbalanced subtrees back into the semi-balanced state. + * + * This implementation of AVL trees has the following peculiarities: + * + * - The AVL specific data structures are physically embedded as fields + * in the "using" data structures. To maintain generality the code + * must constantly translate between "avl_node_t *" and containing + * data structure "void *"s by adding/subracting the avl_offset. + * + * - Since the AVL data is always embedded in other structures, there is + * no locking or memory allocation in the AVL routines. This must be + * provided for by the enclosing data structure's semantics. Typically, + * avl_insert()/_add()/_remove()/avl_insert_here() require some kind of + * exclusive write lock. Other operations require a read lock. + * + * - The implementation uses iteration instead of explicit recursion, + * since it is intended to run on limited size kernel stacks. Since + * there is no recursion stack present to move "up" in the tree, + * there is an explicit "parent" link in the avl_node_t. + * + * - The left/right children pointers of a node are in an array. + * In the code, variables (instead of constants) are used to represent + * left and right indices. The implementation is written as if it only + * dealt with left handed manipulations. By changing the value assigned + * to "left", the code also works for right handed trees. The + * following variables/terms are frequently used: + * + * int left; // 0 when dealing with left children, + * // 1 for dealing with right children + * + * int left_heavy; // -1 when left subtree is taller at some node, + * // +1 when right subtree is taller + * + * int right; // will be the opposite of left (0 or 1) + * int right_heavy;// will be the opposite of left_heavy (-1 or 1) + * + * int direction; // 0 for "<" (ie. left child); 1 for ">" (right) + * + * Though it is a little more confusing to read the code, the approach + * allows using half as much code (and hence cache footprint) for tree + * manipulations and eliminates many conditional branches. + * + * - The avl_index_t is an opaque "cookie" used to find nodes at or + * adjacent to where a new value would be inserted in the tree. The value + * is a modified "avl_node_t *". The bottom bit (normally 0 for a + * pointer) is set to indicate if that the new node has a value greater + * than the value of the indicated "avl_node_t *". + */ + +#include <sys/types.h> +#include <sys/param.h> +#include <sys/debug.h> +#include <sys/avl.h> +#include <sys/cmn_err.h> + +/* + * Small arrays to translate between balance (or diff) values and child indeces. + * + * Code that deals with binary tree data structures will randomly use + * left and right children when examining a tree. C "if()" statements + * which evaluate randomly suffer from very poor hardware branch prediction. + * In this code we avoid some of the branch mispredictions by using the + * following translation arrays. They replace random branches with an + * additional memory reference. Since the translation arrays are both very + * small the data should remain efficiently in cache. + */ +static const int avl_child2balance[2] = {-1, 1}; +static const int avl_balance2child[] = {0, 0, 1}; + + +/* + * Walk from one node to the previous valued node (ie. an infix walk + * towards the left). At any given node we do one of 2 things: + * + * - If there is a left child, go to it, then to it's rightmost descendant. + * + * - otherwise we return thru parent nodes until we've come from a right child. + * + * Return Value: + * NULL - if at the end of the nodes + * otherwise next node + */ +void * +avl_walk(avl_tree_t *tree, void *oldnode, int left) +{ + size_t off = tree->avl_offset; + avl_node_t *node = AVL_DATA2NODE(oldnode, off); + int right = 1 - left; + int was_child; + + + /* + * nowhere to walk to if tree is empty + */ + if (node == NULL) + return (NULL); + + /* + * Visit the previous valued node. There are two possibilities: + * + * If this node has a left child, go down one left, then all + * the way right. + */ + if (node->avl_child[left] != NULL) { + for (node = node->avl_child[left]; + node->avl_child[right] != NULL; + node = node->avl_child[right]) + ; + /* + * Otherwise, return thru left children as far as we can. + */ + } else { + for (;;) { + was_child = AVL_XCHILD(node); + node = AVL_XPARENT(node); + if (node == NULL) + return (NULL); + if (was_child == right) + break; + } + } + + return (AVL_NODE2DATA(node, off)); +} + +/* + * Return the lowest valued node in a tree or NULL. + * (leftmost child from root of tree) + */ +void * +avl_first(avl_tree_t *tree) +{ + avl_node_t *node; + avl_node_t *prev = NULL; + size_t off = tree->avl_offset; + + for (node = tree->avl_root; node != NULL; node = node->avl_child[0]) + prev = node; + + if (prev != NULL) + return (AVL_NODE2DATA(prev, off)); + return (NULL); +} + +/* + * Return the highest valued node in a tree or NULL. + * (rightmost child from root of tree) + */ +void * +avl_last(avl_tree_t *tree) +{ + avl_node_t *node; + avl_node_t *prev = NULL; + size_t off = tree->avl_offset; + + for (node = tree->avl_root; node != NULL; node = node->avl_child[1]) + prev = node; + + if (prev != NULL) + return (AVL_NODE2DATA(prev, off)); + return (NULL); +} + +/* + * Access the node immediately before or after an insertion point. + * + * "avl_index_t" is a (avl_node_t *) with the bottom bit indicating a child + * + * Return value: + * NULL: no node in the given direction + * "void *" of the found tree node + */ +void * +avl_nearest(avl_tree_t *tree, avl_index_t where, int direction) +{ + int child = AVL_INDEX2CHILD(where); + avl_node_t *node = AVL_INDEX2NODE(where); + void *data; + size_t off = tree->avl_offset; + + if (node == NULL) { + ASSERT(tree->avl_root == NULL); + return (NULL); + } + data = AVL_NODE2DATA(node, off); + if (child != direction) + return (data); + + return (avl_walk(tree, data, direction)); +} + + +/* + * Search for the node which contains "value". The algorithm is a + * simple binary tree search. + * + * return value: + * NULL: the value is not in the AVL tree + * *where (if not NULL) is set to indicate the insertion point + * "void *" of the found tree node + */ +void * +avl_find(avl_tree_t *tree, void *value, avl_index_t *where) +{ + avl_node_t *node; + avl_node_t *prev = NULL; + int child = 0; + int diff; + size_t off = tree->avl_offset; + + for (node = tree->avl_root; node != NULL; + node = node->avl_child[child]) { + + prev = node; + + diff = tree->avl_compar(value, AVL_NODE2DATA(node, off)); + ASSERT(-1 <= diff && diff <= 1); + if (diff == 0) { +#ifdef DEBUG + if (where != NULL) + *where = 0; +#endif + return (AVL_NODE2DATA(node, off)); + } + child = avl_balance2child[1 + diff]; + + } + + if (where != NULL) + *where = AVL_MKINDEX(prev, child); + + return (NULL); +} + + +/* + * Perform a rotation to restore balance at the subtree given by depth. + * + * This routine is used by both insertion and deletion. The return value + * indicates: + * 0 : subtree did not change height + * !0 : subtree was reduced in height + * + * The code is written as if handling left rotations, right rotations are + * symmetric and handled by swapping values of variables right/left[_heavy] + * + * On input balance is the "new" balance at "node". This value is either + * -2 or +2. + */ +static int +avl_rotation(avl_tree_t *tree, avl_node_t *node, int balance) +{ + int left = !(balance < 0); /* when balance = -2, left will be 0 */ + int right = 1 - left; + int left_heavy = balance >> 1; + int right_heavy = -left_heavy; + avl_node_t *parent = AVL_XPARENT(node); + avl_node_t *child = node->avl_child[left]; + avl_node_t *cright; + avl_node_t *gchild; + avl_node_t *gright; + avl_node_t *gleft; + int which_child = AVL_XCHILD(node); + int child_bal = AVL_XBALANCE(child); + + /* BEGIN CSTYLED */ + /* + * case 1 : node is overly left heavy, the left child is balanced or + * also left heavy. This requires the following rotation. + * + * (node bal:-2) + * / \ + * / \ + * (child bal:0 or -1) + * / \ + * / \ + * cright + * + * becomes: + * + * (child bal:1 or 0) + * / \ + * / \ + * (node bal:-1 or 0) + * / \ + * / \ + * cright + * + * we detect this situation by noting that child's balance is not + * right_heavy. + */ + /* END CSTYLED */ + if (child_bal != right_heavy) { + + /* + * compute new balance of nodes + * + * If child used to be left heavy (now balanced) we reduced + * the height of this sub-tree -- used in "return...;" below + */ + child_bal += right_heavy; /* adjust towards right */ + + /* + * move "cright" to be node's left child + */ + cright = child->avl_child[right]; + node->avl_child[left] = cright; + if (cright != NULL) { + AVL_SETPARENT(cright, node); + AVL_SETCHILD(cright, left); + } + + /* + * move node to be child's right child + */ + child->avl_child[right] = node; + AVL_SETBALANCE(node, -child_bal); + AVL_SETCHILD(node, right); + AVL_SETPARENT(node, child); + + /* + * update the pointer into this subtree + */ + AVL_SETBALANCE(child, child_bal); + AVL_SETCHILD(child, which_child); + AVL_SETPARENT(child, parent); + if (parent != NULL) + parent->avl_child[which_child] = child; + else + tree->avl_root = child; + + return (child_bal == 0); + } + + /* BEGIN CSTYLED */ + /* + * case 2 : When node is left heavy, but child is right heavy we use + * a different rotation. + * + * (node b:-2) + * / \ + * / \ + * / \ + * (child b:+1) + * / \ + * / \ + * (gchild b: != 0) + * / \ + * / \ + * gleft gright + * + * becomes: + * + * (gchild b:0) + * / \ + * / \ + * / \ + * (child b:?) (node b:?) + * / \ / \ + * / \ / \ + * gleft gright + * + * computing the new balances is more complicated. As an example: + * if gchild was right_heavy, then child is now left heavy + * else it is balanced + */ + /* END CSTYLED */ + gchild = child->avl_child[right]; + gleft = gchild->avl_child[left]; + gright = gchild->avl_child[right]; + + /* + * move gright to left child of node and + * + * move gleft to right child of node + */ + node->avl_child[left] = gright; + if (gright != NULL) { + AVL_SETPARENT(gright, node); + AVL_SETCHILD(gright, left); + } + + child->avl_child[right] = gleft; + if (gleft != NULL) { + AVL_SETPARENT(gleft, child); + AVL_SETCHILD(gleft, right); + } + + /* + * move child to left child of gchild and + * + * move node to right child of gchild and + * + * fixup parent of all this to point to gchild + */ + balance = AVL_XBALANCE(gchild); + gchild->avl_child[left] = child; + AVL_SETBALANCE(child, (balance == right_heavy ? left_heavy : 0)); + AVL_SETPARENT(child, gchild); + AVL_SETCHILD(child, left); + + gchild->avl_child[right] = node; + AVL_SETBALANCE(node, (balance == left_heavy ? right_heavy : 0)); + AVL_SETPARENT(node, gchild); + AVL_SETCHILD(node, right); + + AVL_SETBALANCE(gchild, 0); + AVL_SETPARENT(gchild, parent); + AVL_SETCHILD(gchild, which_child); + if (parent != NULL) + parent->avl_child[which_child] = gchild; + else + tree->avl_root = gchild; + + return (1); /* the new tree is always shorter */ +} + + +/* + * Insert a new node into an AVL tree at the specified (from avl_find()) place. + * + * Newly inserted nodes are always leaf nodes in the tree, since avl_find() + * searches out to the leaf positions. The avl_index_t indicates the node + * which will be the parent of the new node. + * + * After the node is inserted, a single rotation further up the tree may + * be necessary to maintain an acceptable AVL balance. + */ +void +avl_insert(avl_tree_t *tree, void *new_data, avl_index_t where) +{ + avl_node_t *node; + avl_node_t *parent = AVL_INDEX2NODE(where); + int old_balance; + int new_balance; + int which_child = AVL_INDEX2CHILD(where); + size_t off = tree->avl_offset; + + ASSERT(tree); +#ifdef _LP64 + ASSERT(((uintptr_t)new_data & 0x7) == 0); +#endif + + node = AVL_DATA2NODE(new_data, off); + + /* + * First, add the node to the tree at the indicated position. + */ + ++tree->avl_numnodes; + + node->avl_child[0] = NULL; + node->avl_child[1] = NULL; + + AVL_SETCHILD(node, which_child); + AVL_SETBALANCE(node, 0); + AVL_SETPARENT(node, parent); + if (parent != NULL) { + ASSERT(parent->avl_child[which_child] == NULL); + parent->avl_child[which_child] = node; + } else { + ASSERT(tree->avl_root == NULL); + tree->avl_root = node; + } + /* + * Now, back up the tree modifying the balance of all nodes above the + * insertion point. If we get to a highly unbalanced ancestor, we + * need to do a rotation. If we back out of the tree we are done. + * If we brought any subtree into perfect balance (0), we are also done. + */ + for (;;) { + node = parent; + if (node == NULL) + return; + + /* + * Compute the new balance + */ + old_balance = AVL_XBALANCE(node); + new_balance = old_balance + avl_child2balance[which_child]; + + /* + * If we introduced equal balance, then we are done immediately + */ + if (new_balance == 0) { + AVL_SETBALANCE(node, 0); + return; + } + + /* + * If both old and new are not zero we went + * from -1 to -2 balance, do a rotation. + */ + if (old_balance != 0) + break; + + AVL_SETBALANCE(node, new_balance); + parent = AVL_XPARENT(node); + which_child = AVL_XCHILD(node); + } + + /* + * perform a rotation to fix the tree and return + */ + (void) avl_rotation(tree, node, new_balance); +} + +/* + * Insert "new_data" in "tree" in the given "direction" either after or + * before (AVL_AFTER, AVL_BEFORE) the data "here". + * + * Insertions can only be done at empty leaf points in the tree, therefore + * if the given child of the node is already present we move to either + * the AVL_PREV or AVL_NEXT and reverse the insertion direction. Since + * every other node in the tree is a leaf, this always works. + * + * To help developers using this interface, we assert that the new node + * is correctly ordered at every step of the way in DEBUG kernels. + */ +void +avl_insert_here( + avl_tree_t *tree, + void *new_data, + void *here, + int direction) +{ + avl_node_t *node; + int child = direction; /* rely on AVL_BEFORE == 0, AVL_AFTER == 1 */ +#ifdef DEBUG + int diff; +#endif + + ASSERT(tree != NULL); + ASSERT(new_data != NULL); + ASSERT(here != NULL); + ASSERT(direction == AVL_BEFORE || direction == AVL_AFTER); + + /* + * If corresponding child of node is not NULL, go to the neighboring + * node and reverse the insertion direction. + */ + node = AVL_DATA2NODE(here, tree->avl_offset); + +#ifdef DEBUG + diff = tree->avl_compar(new_data, here); + ASSERT(-1 <= diff && diff <= 1); + ASSERT(diff != 0); + ASSERT(diff > 0 ? child == 1 : child == 0); +#endif + + if (node->avl_child[child] != NULL) { + node = node->avl_child[child]; + child = 1 - child; + while (node->avl_child[child] != NULL) { +#ifdef DEBUG + diff = tree->avl_compar(new_data, + AVL_NODE2DATA(node, tree->avl_offset)); + ASSERT(-1 <= diff && diff <= 1); + ASSERT(diff != 0); + ASSERT(diff > 0 ? child == 1 : child == 0); +#endif + node = node->avl_child[child]; + } +#ifdef DEBUG + diff = tree->avl_compar(new_data, + AVL_NODE2DATA(node, tree->avl_offset)); + ASSERT(-1 <= diff && diff <= 1); + ASSERT(diff != 0); + ASSERT(diff > 0 ? child == 1 : child == 0); +#endif + } + ASSERT(node->avl_child[child] == NULL); + + avl_insert(tree, new_data, AVL_MKINDEX(node, child)); +} + +/* + * Add a new node to an AVL tree. + */ +void +avl_add(avl_tree_t *tree, void *new_node) +{ + avl_index_t where; + + /* + * This is unfortunate. We want to call panic() here, even for + * non-DEBUG kernels. In userland, however, we can't depend on anything + * in libc or else the rtld build process gets confused. So, all we can + * do in userland is resort to a normal ASSERT(). + */ + if (avl_find(tree, new_node, &where) != NULL) +#ifdef _KERNEL + panic("avl_find() succeeded inside avl_add()"); +#else + ASSERT(0); +#endif + avl_insert(tree, new_node, where); +} + +/* + * Delete a node from the AVL tree. Deletion is similar to insertion, but + * with 2 complications. + * + * First, we may be deleting an interior node. Consider the following subtree: + * + * d c c + * / \ / \ / \ + * b e b e b e + * / \ / \ / + * a c a a + * + * When we are deleting node (d), we find and bring up an adjacent valued leaf + * node, say (c), to take the interior node's place. In the code this is + * handled by temporarily swapping (d) and (c) in the tree and then using + * common code to delete (d) from the leaf position. + * + * Secondly, an interior deletion from a deep tree may require more than one + * rotation to fix the balance. This is handled by moving up the tree through + * parents and applying rotations as needed. The return value from + * avl_rotation() is used to detect when a subtree did not change overall + * height due to a rotation. + */ +void +avl_remove(avl_tree_t *tree, void *data) +{ + avl_node_t *delete; + avl_node_t *parent; + avl_node_t *node; + avl_node_t tmp; + int old_balance; + int new_balance; + int left; + int right; + int which_child; + size_t off = tree->avl_offset; + + ASSERT(tree); + + delete = AVL_DATA2NODE(data, off); + + /* + * Deletion is easiest with a node that has at most 1 child. + * We swap a node with 2 children with a sequentially valued + * neighbor node. That node will have at most 1 child. Note this + * has no effect on the ordering of the remaining nodes. + * + * As an optimization, we choose the greater neighbor if the tree + * is right heavy, otherwise the left neighbor. This reduces the + * number of rotations needed. + */ + if (delete->avl_child[0] != NULL && delete->avl_child[1] != NULL) { + + /* + * choose node to swap from whichever side is taller + */ + old_balance = AVL_XBALANCE(delete); + left = avl_balance2child[old_balance + 1]; + right = 1 - left; + + /* + * get to the previous value'd node + * (down 1 left, as far as possible right) + */ + for (node = delete->avl_child[left]; + node->avl_child[right] != NULL; + node = node->avl_child[right]) + ; + + /* + * create a temp placeholder for 'node' + * move 'node' to delete's spot in the tree + */ + tmp = *node; + + *node = *delete; + if (node->avl_child[left] == node) + node->avl_child[left] = &tmp; + + parent = AVL_XPARENT(node); + if (parent != NULL) + parent->avl_child[AVL_XCHILD(node)] = node; + else + tree->avl_root = node; + AVL_SETPARENT(node->avl_child[left], node); + AVL_SETPARENT(node->avl_child[right], node); + + /* + * Put tmp where node used to be (just temporary). + * It always has a parent and at most 1 child. + */ + delete = &tmp; + parent = AVL_XPARENT(delete); + parent->avl_child[AVL_XCHILD(delete)] = delete; + which_child = (delete->avl_child[1] != 0); + if (delete->avl_child[which_child] != NULL) + AVL_SETPARENT(delete->avl_child[which_child], delete); + } + + + /* + * Here we know "delete" is at least partially a leaf node. It can + * be easily removed from the tree. + */ + ASSERT(tree->avl_numnodes > 0); + --tree->avl_numnodes; + parent = AVL_XPARENT(delete); + which_child = AVL_XCHILD(delete); + if (delete->avl_child[0] != NULL) + node = delete->avl_child[0]; + else + node = delete->avl_child[1]; + + /* + * Connect parent directly to node (leaving out delete). + */ + if (node != NULL) { + AVL_SETPARENT(node, parent); + AVL_SETCHILD(node, which_child); + } + if (parent == NULL) { + tree->avl_root = node; + return; + } + parent->avl_child[which_child] = node; + + + /* + * Since the subtree is now shorter, begin adjusting parent balances + * and performing any needed rotations. + */ + do { + + /* + * Move up the tree and adjust the balance + * + * Capture the parent and which_child values for the next + * iteration before any rotations occur. + */ + node = parent; + old_balance = AVL_XBALANCE(node); + new_balance = old_balance - avl_child2balance[which_child]; + parent = AVL_XPARENT(node); + which_child = AVL_XCHILD(node); + + /* + * If a node was in perfect balance but isn't anymore then + * we can stop, since the height didn't change above this point + * due to a deletion. + */ + if (old_balance == 0) { + AVL_SETBALANCE(node, new_balance); + break; + } + + /* + * If the new balance is zero, we don't need to rotate + * else + * need a rotation to fix the balance. + * If the rotation doesn't change the height + * of the sub-tree we have finished adjusting. + */ + if (new_balance == 0) + AVL_SETBALANCE(node, new_balance); + else if (!avl_rotation(tree, node, new_balance)) + break; + } while (parent != NULL); +} + +/* + * initialize a new AVL tree + */ +void +avl_create(avl_tree_t *tree, int (*compar) (const void *, const void *), + size_t size, size_t offset) +{ + ASSERT(tree); + ASSERT(compar); + ASSERT(size > 0); + ASSERT(size >= offset + sizeof (avl_node_t)); +#ifdef _LP64 + ASSERT((offset & 0x7) == 0); +#endif + + tree->avl_compar = compar; + tree->avl_root = NULL; + tree->avl_numnodes = 0; + tree->avl_size = size; + tree->avl_offset = offset; +} + +/* + * Delete a tree. + */ +/* ARGSUSED */ +void +avl_destroy(avl_tree_t *tree) +{ + ASSERT(tree); + ASSERT(tree->avl_numnodes == 0); + ASSERT(tree->avl_root == NULL); +} + + +/* + * Return the number of nodes in an AVL tree. + */ +ulong_t +avl_numnodes(avl_tree_t *tree) +{ + ASSERT(tree); + return (tree->avl_numnodes); +} + + +#define CHILDBIT (1L) + +/* + * Post-order tree walk used to visit all tree nodes and destroy the tree + * in post order. This is used for destroying a tree w/o paying any cost + * for rebalancing it. + * + * example: + * + * void *cookie = NULL; + * my_data_t *node; + * + * while ((node = avl_destroy_nodes(tree, &cookie)) != NULL) + * free(node); + * avl_destroy(tree); + * + * The cookie is really an avl_node_t to the current node's parent and + * an indication of which child you looked at last. + * + * On input, a cookie value of CHILDBIT indicates the tree is done. + */ +void * +avl_destroy_nodes(avl_tree_t *tree, void **cookie) +{ + avl_node_t *node; + avl_node_t *parent; + int child; + void *first; + size_t off = tree->avl_offset; + + /* + * Initial calls go to the first node or it's right descendant. + */ + if (*cookie == NULL) { + first = avl_first(tree); + + /* + * deal with an empty tree + */ + if (first == NULL) { + *cookie = (void *)CHILDBIT; + return (NULL); + } + + node = AVL_DATA2NODE(first, off); + parent = AVL_XPARENT(node); + goto check_right_side; + } + + /* + * If there is no parent to return to we are done. + */ + parent = (avl_node_t *)((uintptr_t)(*cookie) & ~CHILDBIT); + if (parent == NULL) { + if (tree->avl_root != NULL) { + ASSERT(tree->avl_numnodes == 1); + tree->avl_root = NULL; + tree->avl_numnodes = 0; + } + return (NULL); + } + + /* + * Remove the child pointer we just visited from the parent and tree. + */ + child = (uintptr_t)(*cookie) & CHILDBIT; + parent->avl_child[child] = NULL; + ASSERT(tree->avl_numnodes > 1); + --tree->avl_numnodes; + + /* + * If we just did a right child or there isn't one, go up to parent. + */ + if (child == 1 || parent->avl_child[1] == NULL) { + node = parent; + parent = AVL_XPARENT(parent); + goto done; + } + + /* + * Do parent's right child, then leftmost descendent. + */ + node = parent->avl_child[1]; + while (node->avl_child[0] != NULL) { + parent = node; + node = node->avl_child[0]; + } + + /* + * If here, we moved to a left child. It may have one + * child on the right (when balance == +1). + */ +check_right_side: + if (node->avl_child[1] != NULL) { + ASSERT(AVL_XBALANCE(node) == 1); + parent = node; + node = node->avl_child[1]; + ASSERT(node->avl_child[0] == NULL && + node->avl_child[1] == NULL); + } else { + ASSERT(AVL_XBALANCE(node) <= 0); + } + +done: + if (parent == NULL) { + *cookie = (void *)CHILDBIT; + ASSERT(node == tree->avl_root); + } else { + *cookie = (void *)((uintptr_t)parent | AVL_XCHILD(node)); + } + + return (AVL_NODE2DATA(node, off)); +} |