/**
* This does a single "left" rotation on a given node 'a'. The rotated
* node is returned.
*
* @private
* @param a the node to rotate.
* @return the rotated node
*/
static PropPtr
rotate_left_single(PropPtr a)
{
PropPtr b = a->right;
a->right = b->left;
b->left = a;
fixup_height(a);
fixup_height(b);
return b;
}
static PropPtr
rotate_right_single(PropPtr a)
{
PropPtr b = AVL_LF(a);
AVL_LF(a) = AVL_RT(b);
AVL_RT(b) = a;
fixup_height(a);
fixup_height(b);
return (b);
}
/**
* This call balances the AVL node 'a' and returns the balanced node.
*
* @private
* @param a the node to balance
* @return the balanced node
*/
static PropPtr
balance_node(PropPtr a)
{
int dh = height_diff(a);
if (abs(dh) < 2) {
fixup_height(a);
} else {
/* One might argue the brackets are not necessary here, but
* this looked like a train wreck without them :)
*/
if (dh == 2) {
if (height_diff(a->right) >= 0) {
a = rotate_left_single(a);
} else {
a = rotate_left_double(a);
}
} else if (height_diff(a->left) <= 0) {
a = rotate_right_single(a);
} else {
a = rotate_right_double(a);
}
}
return a;
}
/**
* This does a double "right" rotation on a given node 'a'. The rotated
* node is returned.
*
* @private
* @param a the node to rotate.
* @return the rotated node
*/
static PropPtr
rotate_right_double(PropPtr a)
{
PropPtr b = a->left, c = b->right;
a->left = c->right;
b->right = c->left;
c->right = a;
c->left = b;
fixup_height(a);
fixup_height(b);
fixup_height(c);
return c;
}
static PropPtr
rotate_left_double(PropPtr a)
{
PropPtr b = AVL_RT(a), c = AVL_LF(b);
AVL_RT(a) = AVL_LF(c);
AVL_LF(b) = AVL_RT(c);
AVL_LF(c) = a;
AVL_RT(c) = b;
fixup_height(a);
fixup_height(b);
fixup_height(c);
return c;
}
static PropPtr
balance_node(PropPtr a)
{
int dh = height_diff(a);
if (abs(dh) < 2) {
fixup_height(a);
} else {
if (dh == 2)
if (height_diff(AVL_RT(a)) >= 0)
a = rotate_left_single(a);
else
a = rotate_left_double(a);
else if (height_diff(AVL_LF(a)) <= 0)
a = rotate_right_single(a);
else
a = rotate_right_double(a);
}
return a;
}