linux-kernel - [PATCH v2 4/9] rbtree: place easiest case first in rb

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Message-Id: <1343946858-8170-5-git-send-email-walken@google.com>
Date:	Thu,  2 Aug 2012 15:34:13 -0700
From:	Michel Lespinasse <walken@...gle.com>
To:	riel@...hat.com, peterz@...radead.org, daniel.santos@...ox.com,
	aarcange@...hat.com, dwmw2@...radead.org, akpm@...ux-foundation.org
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	torvalds@...ux-foundation.org
Subject: [PATCH v2 4/9] rbtree: place easiest case first in rb_erase()

In rb_erase, move the easy case (node to erase has no more than
1 child) first. I feel the code reads easier that way.

Signed-off-by: Michel Lespinasse <walken@...gle.com>
---
 lib/rbtree.c |   35 ++++++++++++++++++-----------------
 1 files changed, 18 insertions(+), 17 deletions(-)

diff --git a/lib/rbtree.c b/lib/rbtree.c
index de89a61..bde1b5c 100644
--- a/lib/rbtree.c
+++ b/lib/rbtree.c
@@ -368,17 +368,28 @@ 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, *parent;
+	struct rb_node *child = node->rb_right, *tmp = node->rb_left;
+	struct rb_node *parent;
 	int color;
 
-	if (!node->rb_left)
-		child = node->rb_right;
-	else if (!node->rb_right)
-		child = node->rb_left;
-	else {
+	if (!tmp) {
+	case1:
+		/* Case 1: node to erase has no more than 1 child (easy!) */
+
+		parent = rb_parent(node);
+		color = rb_color(node);
+
+		if (child)
+			rb_set_parent(child, parent);
+		__rb_change_child(node, child, parent, root);
+	} else if (!child) {
+		/* Still case 1, but this time the child is node->rb_left */
+		child = tmp;
+		goto case1;
+	} else {
 		struct rb_node *old = node, *left;
 
-		node = node->rb_right;
+		node = child;
 		while ((left = node->rb_left) != NULL)
 			node = left;
 
@@ -402,18 +413,8 @@ void rb_erase(struct rb_node *node, struct rb_root *root)
 		node->__rb_parent_color = old->__rb_parent_color;
 		node->rb_left = old->rb_left;
 		rb_set_parent(old->rb_left, node);
-
-		goto color;
 	}
 
-	parent = rb_parent(node);
-	color = rb_color(node);
-
-	if (child)
-		rb_set_parent(child, parent);
-	__rb_change_child(node, child, parent, root);
-
-color:
 	if (color == RB_BLACK)
 		__rb_erase_color(child, parent, root);
 }
-- 
1.7.7.3

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