/* Returns the next data item in inorder
within the tree being traversed with |trav|,
or if there are no more data items returns |0|. */
static Std$Object_t *avl_t_next (struct avl_traverser *trav) {
struct avl_node *x;
if (trav->avl_generation != trav->avl_table->avl_generation) trav_refresh (trav);
x = trav->avl_node;
if (x == 0) {
return avl_t_first (trav, trav->avl_table);
} else if (x->avl_link[1] != 0) {
trav->avl_stack[trav->avl_height++] = x;
x = x->avl_link[1];
while (x->avl_link[0] != 0) {
trav->avl_stack[trav->avl_height++] = x;
x = x->avl_link[0];
}
} else {
struct avl_node *y;
do {
if (trav->avl_height == 0) {
trav->avl_node = 0;
return 0;
}
y = x;
x = trav->avl_stack[--trav->avl_height];
} while (y == x->avl_link[1]);
}
trav->avl_node = x;
return x;
}
/* Returns the previous data item in inorder
within the tree being traversed with |trav|,
or if there are no more data items returns |NULL|. */
void *
bst_t_prev (struct bst_traverser *trav)
{
struct bst_node *x;
assert (trav != NULL);
if (trav->bst_generation != trav->bst_table->bst_generation)
trav_refresh (trav);
x = trav->bst_node;
if (x == NULL)
{
return bst_t_last (trav, trav->bst_table);
}
else if (x->bst_link[0] != NULL)
{
if (trav->bst_height >= BST_MAX_HEIGHT)
{
bst_balance (trav->bst_table);
return bst_t_prev (trav);
}
trav->bst_stack[trav->bst_height++] = x;
x = x->bst_link[0];
while (x->bst_link[1] != NULL)
{
if (trav->bst_height >= BST_MAX_HEIGHT)
{
bst_balance (trav->bst_table);
return bst_t_prev (trav);
}
trav->bst_stack[trav->bst_height++] = x;
x = x->bst_link[1];
}
}
else
{
struct bst_node *y;
do
{
if (trav->bst_height == 0)
{
trav->bst_node = NULL;
return NULL;
}
y = x;
x = trav->bst_stack[--trav->bst_height];
}
while (y == x->bst_link[0]);
}
trav->bst_node = x;
return x->bst_data;
}
