diff options
| -rw-r--r-- | lib/rbtree.c | 105 |
1 files changed, 62 insertions, 43 deletions
diff --git a/lib/rbtree.c b/lib/rbtree.c index bde1b5c5fb3..80b092538fa 100644 --- a/lib/rbtree.c +++ b/lib/rbtree.c @@ -2,7 +2,8 @@ Red Black Trees (C) 1999 Andrea Arcangeli <andrea@suse.de> (C) 2002 David Woodhouse <dwmw2@infradead.org> - + (C) 2012 Michel Lespinasse <walken@google.com> + 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 2 of the License, or @@ -50,6 +51,11 @@ #define rb_is_red(r) (!rb_color(r)) #define rb_is_black(r) rb_color(r) +static inline void rb_set_black(struct rb_node *rb) +{ + rb->__rb_parent_color |= RB_BLACK; +} + static inline void rb_set_parent(struct rb_node *rb, struct rb_node *p) { rb->__rb_parent_color = rb_color(rb) | (unsigned long)p; @@ -214,27 +220,18 @@ void rb_insert_color(struct rb_node *node, struct rb_root *root) } EXPORT_SYMBOL(rb_insert_color); -static void __rb_erase_color(struct rb_node *node, struct rb_node *parent, - struct rb_root *root) +static void __rb_erase_color(struct rb_node *parent, struct rb_root *root) { - struct rb_node *sibling, *tmp1, *tmp2; + struct rb_node *node = NULL, *sibling, *tmp1, *tmp2; while (true) { /* - * Loop invariant: all leaf paths going through node have a - * black node count that is 1 lower than other leaf paths. - * - * If node is red, we can flip it to black to adjust. - * If node is the root, all leaf paths go through it. - * Otherwise, we need to adjust the tree through color flips - * and tree rotations as per one of the 4 cases below. + * Loop invariants: + * - node is black (or NULL on first iteration) + * - node is not the root (parent is not NULL) + * - All leaf paths going through parent and node have a + * black node count that is 1 lower than other leaf paths. */ - if (node && rb_is_red(node)) { - rb_set_parent_color(node, parent, RB_BLACK); - break; - } else if (!parent) { - break; - } sibling = parent->rb_right; if (node != sibling) { /* node == parent->rb_left */ if (rb_is_red(sibling)) { @@ -268,17 +265,22 @@ static void __rb_erase_color(struct rb_node *node, struct rb_node *parent, * / \ / \ * Sl Sr Sl Sr * - * This leaves us violating 5), so - * recurse at p. If p is red, the - * recursion will just flip it to black - * and exit. If coming from Case 1, - * p is known to be red. + * This leaves us violating 5) which + * can be fixed by flipping p to black + * if it was red, or by recursing at p. + * p is red when coming from Case 1. */ rb_set_parent_color(sibling, parent, RB_RED); - node = parent; - parent = rb_parent(node); - continue; + if (rb_is_red(parent)) + rb_set_black(parent); + else { + node = parent; + parent = rb_parent(node); + if (parent) + continue; + } + break; } /* * Case 3 - right rotate at sibling @@ -339,9 +341,15 @@ static void __rb_erase_color(struct rb_node *node, struct rb_node *parent, /* Case 2 - sibling color flip */ rb_set_parent_color(sibling, parent, RB_RED); - node = parent; - parent = rb_parent(node); - continue; + if (rb_is_red(parent)) + rb_set_black(parent); + else { + node = parent; + parent = rb_parent(node); + if (parent) + continue; + } + break; } /* Case 3 - right rotate at sibling */ sibling->rb_right = tmp1 = tmp2->rb_left; @@ -369,23 +377,31 @@ static void __rb_erase_color(struct rb_node *node, struct rb_node *parent, void rb_erase(struct rb_node *node, struct rb_root *root) { struct rb_node *child = node->rb_right, *tmp = node->rb_left; - struct rb_node *parent; - int color; + struct rb_node *parent, *rebalance; if (!tmp) { - case1: - /* Case 1: node to erase has no more than 1 child (easy!) */ + /* + * 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. + */ parent = rb_parent(node); - color = rb_color(node); - - if (child) - rb_set_parent(child, parent); __rb_change_child(node, child, parent, root); + if (child) { + rb_set_parent_color(child, parent, RB_BLACK); + rebalance = NULL; + } else { + rebalance = rb_is_black(node) ? parent : NULL; + } } else if (!child) { /* Still case 1, but this time the child is node->rb_left */ - child = tmp; - goto case1; + parent = rb_parent(node); + __rb_change_child(node, tmp, parent, root); + rb_set_parent_color(tmp, parent, RB_BLACK); + rebalance = NULL; } else { struct rb_node *old = node, *left; @@ -397,26 +413,29 @@ void rb_erase(struct rb_node *node, struct rb_root *root) child = node->rb_right; parent = rb_parent(node); - color = rb_color(node); if (parent == old) { parent = node; } else { - if (child) - rb_set_parent(child, parent); parent->rb_left = child; node->rb_right = old->rb_right; rb_set_parent(old->rb_right, node); } + if (child) { + rb_set_parent_color(child, parent, RB_BLACK); + rebalance = NULL; + } else { + rebalance = rb_is_black(node) ? parent : NULL; + } node->__rb_parent_color = old->__rb_parent_color; node->rb_left = old->rb_left; rb_set_parent(old->rb_left, node); } - if (color == RB_BLACK) - __rb_erase_color(child, parent, root); + if (rebalance) + __rb_erase_color(rebalance, root); } EXPORT_SYMBOL(rb_erase); |