/* Inserts |item| into |tree| and returns a pointer to |item|'s address. If a duplicate item is found in the tree, returns a pointer to the duplicate without inserting |item|. Returns |NULL| in case of memory allocation failure. */ void ** avl_probe (struct avl_table *tree, void *item) { struct avl_node *y, *z; /* Top node to update balance factor, and parent. */ struct avl_node *p, *q; /* Iterator, and parent. */ struct avl_node *n; /* Newly inserted node. */ struct avl_node *w; /* New root of rebalanced subtree. */ int dir; /* Direction to descend. */ unsigned char da[AVL_MAX_HEIGHT]; /* Cached comparison results. */ int k = 0; /* Number of cached results. */ assert (tree != NULL && item != NULL); z = (struct avl_node *) &tree->avl_root; y = tree->avl_root; dir = 0; for (q = z, p = y; p != NULL; q = p, p = p->avl_link[dir]) { int cmp = tree->avl_compare (item, p->avl_data, tree->avl_param); if (cmp == 0) return &p->avl_data; if (p->avl_balance != 0) z = q, y = p, k = 0; da[k++] = dir = cmp > 0; } n = q->avl_link[dir] = tree->avl_alloc->libavl_malloc (tree->avl_alloc, sizeof *n); if (n == NULL) return NULL; tree->avl_count++; n->avl_data = item; n->avl_link[0] = n->avl_link[1] = NULL; n->avl_balance = 0; if (y == NULL) return &n->avl_data; for (p = y, k = 0; p != n; p = p->avl_link[da[k]], k++) if (da[k] == 0) p->avl_balance--; else p->avl_balance++; if (y->avl_balance == -2) { struct avl_node *x = y->avl_link[0]; if (x->avl_balance == -1) { w = x; y->avl_link[0] = x->avl_link[1]; x->avl_link[1] = y; x->avl_balance = y->avl_balance = 0; } else { assert (x->avl_balance == +1); w = x->avl_link[1]; x->avl_link[1] = w->avl_link[0]; w->avl_link[0] = x; y->avl_link[0] = w->avl_link[1]; w->avl_link[1] = y; if (w->avl_balance == -1) x->avl_balance = 0, y->avl_balance = +1; else if (w->avl_balance == 0) x->avl_balance = y->avl_balance = 0; else /* |w->avl_balance == +1| */ x->avl_balance = -1, y->avl_balance = 0; w->avl_balance = 0; } } else if (y->avl_balance == +2) { struct avl_node *x = y->avl_link[1]; if (x->avl_balance == +1) { w = x; y->avl_link[1] = x->avl_link[0]; x->avl_link[0] = y; x->avl_balance = y->avl_balance = 0; } else { assert (x->avl_balance == -1); w = x->avl_link[0]; x->avl_link[0] = w->avl_link[1]; w->avl_link[1] = x; y->avl_link[1] = w->avl_link[0]; w->avl_link[0] = y; if (w->avl_balance == +1) x->avl_balance = 0, y->avl_balance = -1; else if (w->avl_balance == 0) x->avl_balance = y->avl_balance = 0; else /* |w->avl_balance == -1| */ x->avl_balance = +1, y->avl_balance = 0; w->avl_balance = 0; } } else return &n->avl_data; z->avl_link[y != z->avl_link[0]] = w; tree->avl_generation++; return &n->avl_data; }