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Subject[PATCH 2/6] rbtree: optimize fetching of sibling node
Date
When looking to fetch a node's sibling, we went through a sequence of:
- check if node is the parent's left child
- if it is, then fetch the parent's right child

This can be replaced with:
- fetch the parent's right child as an assumed sibling
- check that node is NOT the fetched child

This avoids fetching the parent's left child when node is actually
that child. Saves a bit on code size, though it doesn't seem to make
a large difference in speed.

Signed-off-by: Michel Lespinasse <walken@google.com>
---
lib/rbtree.c | 21 +++++++++++++--------
1 files changed, 13 insertions(+), 8 deletions(-)
diff --git a/lib/rbtree.c b/lib/rbtree.c
index 3b6ec98..8b111cc 100644
--- a/lib/rbtree.c
+++ b/lib/rbtree.c
@@ -108,8 +108,8 @@ void rb_insert_color(struct rb_node *node, struct rb_root *root)

gparent = rb_red_parent(parent);

- if (parent == gparent->rb_left) {
- tmp = gparent->rb_right;
+ tmp = gparent->rb_right;
+ if (parent != tmp) { /* parent == gparent->rb_left */
if (tmp && rb_is_red(tmp)) {
/*
* Case 1 - color flips
@@ -132,7 +132,8 @@ void rb_insert_color(struct rb_node *node, struct rb_root *root)
continue;
}

- if (parent->rb_right == node) {
+ tmp = parent->rb_right;
+ if (node == tmp) {
/*
* Case 2 - left rotate at parent
*
@@ -152,6 +153,7 @@ void rb_insert_color(struct rb_node *node, struct rb_root *root)
RB_BLACK);
rb_set_parent_color(parent, node, RB_RED);
parent = node;
+ tmp = node->rb_right;
}

/*
@@ -163,7 +165,7 @@ void rb_insert_color(struct rb_node *node, struct rb_root *root)
* / \
* n U
*/
- gparent->rb_left = tmp = parent->rb_right;
+ gparent->rb_left = tmp; /* == parent->rb_right */
parent->rb_right = gparent;
if (tmp)
rb_set_parent_color(tmp, gparent, RB_BLACK);
@@ -181,7 +183,8 @@ void rb_insert_color(struct rb_node *node, struct rb_root *root)
continue;
}

- if (parent->rb_left == node) {
+ tmp = parent->rb_left;
+ if (node == tmp) {
/* Case 2 - right rotate at parent */
parent->rb_left = tmp = node->rb_right;
node->rb_right = parent;
@@ -190,10 +193,11 @@ void rb_insert_color(struct rb_node *node, struct rb_root *root)
RB_BLACK);
rb_set_parent_color(parent, node, RB_RED);
parent = node;
+ tmp = node->rb_left;
}

/* Case 3 - left rotate at gparent */
- gparent->rb_right = tmp = parent->rb_left;
+ gparent->rb_right = tmp; /* == parent->rb_left */
parent->rb_left = gparent;
if (tmp)
rb_set_parent_color(tmp, gparent, RB_BLACK);
@@ -224,8 +228,9 @@ static void __rb_erase_color(struct rb_node *node, struct rb_node *parent,
break;
} else if (!parent) {
break;
- } else if (parent->rb_left == node) {
- sibling = parent->rb_right;
+ }
+ sibling = parent->rb_right;
+ if (node != sibling) { /* node == parent->rb_left */
if (rb_is_red(sibling)) {
/*
* Case 1 - left rotate at parent
--
1.7.7.3


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