[PATCH 2/3] Further optimization of function rb_erase() in lib/rbtree.c

Wolfram Strepp
2009-04-10T10:24:21Z

There are two cases when a node, having 2 childs, is erased:
'normal case': the successor is not the right-hand-child of the node to be erased
'special case': the successor is the right-hand child of the node to be erased

Here some ascii-art, with following symbols (referring to the code):
O: node to be deleted
N: the successor of O
P: parent of N
C: child of N
L: some other node

normal case:

O N
/ \ / \
/ \ / \
L \ L \
/ \ P ----> / \ P
/ \ / \
/ /
N C
\ / \
\
C
/ \

special case:
O|P N
/ \ / \
/ \ / \
L \ L \
/ \ N ----> / C
\ / \
\
C
/ \

Notice that for the special case we don't have to reconnect C to N.

Signed-off-by: Wolfram Strepp <wstrepp@gmx.de>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
---
lib/rbtree.c | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)
Index: linux-2.6/lib/rbtree.c
===================================================================
--- linux-2.6.orig/lib/rbtree.c
+++ linux-2.6/lib/rbtree.c
@@ -251,13 +251,13 @@ void rb_erase(struct rb_node *node, stru
parent = rb_parent(node);
color = rb_color(node);

- if (child)
- rb_set_parent(child, parent);
if (parent == old) {
- parent->rb_right = child;
parent = node;
- } else
+ } else {
+ if (child)
+ rb_set_parent(child, parent);
parent->rb_left = child;
+ }

node->rb_parent_color = old->rb_parent_color;
node->rb_right = old->rb_right;

--
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