fix: another case where offsets could be non-zero with no intervals

Author: Dr-Emann

roaring/src/bitmap/store/interval_store.rs

@@ -660,15 +660,15 @@ impl<I: SliceIterator<Interval>> RunIter<I> {
             self.forward_offset = 0;
             return;
         }
+        let only_interval = self.intervals.as_slice().len() == 1;
         let total_offset = u64::from(self.forward_offset)
-            + if self.intervals.as_slice().len() == 1 {
-                u64::from(self.backward_offset)
-            } else {
-                0
-            };
+            + if only_interval { u64::from(self.backward_offset) } else { 0 };
         if Some(total_offset) >= self.intervals.as_slice().first().map(|f| f.run_len()) {
             self.intervals.next();
             self.forward_offset = 0;
+            if only_interval {
+                self.backward_offset = 0;
+            }
         }
     }
 
@@ -680,11 +680,15 @@ impl<I: SliceIterator<Interval>> RunIter<I> {
             self.backward_offset = 0;
             return;
         }
+        let only_interval = self.intervals.as_slice().len() == 1;
         let total_offset = u64::from(self.backward_offset)
-            + if self.intervals.as_slice().len() == 1 { u64::from(self.forward_offset) } else { 0 };
+            + if only_interval { u64::from(self.forward_offset) } else { 0 };
         if Some(total_offset) >= self.intervals.as_slice().last().map(|f| f.run_len()) {
             self.intervals.next_back();
             self.backward_offset = 0;
+            if only_interval {
+                self.forward_offset = 0;
+            }
         }
     }
 

roaring/tests/iter_advance_to.rs

@@ -267,6 +267,17 @@ fn advance_run_with_nth() {
     assert_eq!(iter.nth(100563), None);
 }
 
+#[test]
+fn advance_to_with_next_len() {
+    let mut bitmap = RoaringBitmap::new();
+    bitmap.insert_range(100..0x4000);
+    let mut iter = bitmap.iter();
+    iter.advance_back_to(100);
+    assert_eq!(iter.next(), Some(100));
+    assert_eq!(iter.len(), 0);
+    assert_eq!(iter.nth_back(0), None);
+}
+
 #[test]
 fn advance_bitset_front_and_back_past_each_other() {
     let mut bitmap = RoaringBitmap::new();