fix tdelete to properly balance the tree

the tsearch data structure is an avl tree, but it did not implement
the deletion operation correctly so the tree could become unbalanced.

reported by Ed Schouten.

diff --git a/src/search/tsearch_avl.c b/src/search/tsearch_avl.c
index 86200928ef6c6390a0d8c8563d7a375e92c01605..08644607abf5192dde18342c493c6f98cd914ecb 100644 (file)
--- a/src/search/tsearch_avl.c
+++ b/src/search/tsearch_avl.c
@@ -105,10 +105,13 @@ static struct node *insert(struct node **n, const void *k,
        return r;
 }
 
-static struct node *movr(struct node *n, struct node *r) {
-       if (!n)
-               return r;
-       n->right = movr(n->right, r);
+static struct node *remove_rightmost(struct node *n, struct node **rightmost)
+{
+       if (!n->right) {
+               *rightmost = n;
+               return n->left;
+       }
+       n->right = remove_rightmost(n->right, rightmost);
        return balance(n);
 }
 
@@ -122,7 +125,13 @@ static struct node *remove(struct node **n, const void *k,
        c = cmp(k, (*n)->key);
        if (c == 0) {
                struct node *r = *n;
-               *n = movr(r->left, r->right);
+               if (r->left) {
+                       r->left = remove_rightmost(r->left, n);
+                       (*n)->left = r->left;
+                       (*n)->right = r->right;
+                       *n = balance(*n);
+               } else
+                       *n = r->right;
                free(r);
                return parent;
        }