+/* Delete all the elements with rank between start and end from the skiplist.
+ * Start and end are inclusive. */
+static unsigned long zslDeleteRangeByRank(zskiplist *zsl, unsigned int start, unsigned int end, dict *dict) {
+ zskiplistNode *update[ZSKIPLIST_MAXLEVEL], *x;
+ unsigned long traversed = 0, removed = 0;
+ int i;
+
+ /* start and end are given 0-based, but zsl uses 1-based
+ * ranks internally */
+ start++; end++;
+
+ x = zsl->header;
+ for (i = zsl->level-1; i >= 0; i--) {
+ while (x->forward[i] && (traversed + (i > 0 ? x->span[i-1] : 1)) < start) {
+ traversed += i > 0 ? x->span[i-1] : 1;
+ x = x->forward[i];
+ }
+ update[i] = x;
+ }
+
+ traversed++;
+ x = x->forward[0];
+ while (x && traversed <= end) {
+ zskiplistNode *next;
+
+ for (i = 0; i < zsl->level; i++) {
+ if (update[i]->forward[i] == x) {
+ if (i > 0) {
+ update[i]->span[i-1] += x->span[i-1] - 1;
+ }
+ update[i]->forward[i] = x->forward[i];
+ } else {
+ /* invariant: i > 0, because update[0]->forward[0]
+ * is always equal to x */
+ update[i]->span[i-1] -= 1;
+ }
+ }
+ if (x->forward[0]) {
+ x->forward[0]->backward = x->backward;
+ } else {
+ zsl->tail = x->backward;
+ }
+ next = x->forward[0];
+ dictDelete(dict,x->obj);
+ zslFreeNode(x);
+ while(zsl->level > 1 && zsl->header->forward[zsl->level-1] == NULL)
+ zsl->level--;
+ zsl->length--;
+ removed++;
+ traversed++;
+ x = next;
+ }
+ return removed;
+}
+