fix(treemap): remove_range would sometimes remove too much

remove_range would remove the whole container if the first bitmap found
in the range was the last bigmap touching the range, rather than just
the first part of the container.

croaring/src/treemap/imp.rs

@@ -446,35 +446,31 @@ impl Treemap {
             return;
         }
 
-        let mut iter = self.map.range_mut(start_high..=end_high);
-        let mut keys_to_remove = Vec::new();
         // Step 1: Remove first partial range if bitmap exists
-        if let Some((&first_high, first_bitmap)) = iter.next() {
-            if first_high == start_high {
-                first_bitmap.remove_range(start_low..=u32::MAX);
-                if first_bitmap.is_empty() {
-                    keys_to_remove.push(first_high);
-                }
-            } else {
-                keys_to_remove.push(first_high);
+        if let Entry::Occupied(mut e) = self.map.entry(start_high) {
+            let bitmap = e.get_mut();
+            bitmap.remove_range(start_low..);
+            if bitmap.is_empty() {
+                e.remove();
             }
         }
         // Step 2: Remove the final partial range if bitmap exists
-        if let Some((&last_high, last_bitmap)) = iter.next_back() {
-            if last_high == end_high {
-                last_bitmap.remove_range(0..=end_low);
-                if last_bitmap.is_empty() {
-                    keys_to_remove.push(last_high);
-                }
-            } else {
-                keys_to_remove.push(last_high);
+        if let Entry::Occupied(mut e) = self.map.entry(end_high) {
+            let bitmap = e.get_mut();
+            bitmap.remove_range(..=end_low);
+            if bitmap.is_empty() {
+                e.remove();
             }
         }
 
         // Step 3: Remove all full ranges
         // Unfortunately, there's no way to remove a range from a BTreeMap, so
         // we have to build a list of keys to remove and then remove them individually
-        keys_to_remove.extend(iter.map(|(&k, _)| k));
+        let keys_to_remove = self
+            .map
+            .range_mut(start_high + 1..end_high)
+            .map(|(&k, _)| k)
+            .collect::<Vec<_>>();
 
         for key in &keys_to_remove {
             self.map.remove(key);

croaring/tests/lib.rs

@@ -180,6 +180,19 @@ fn test_treemap_max_andnot_empty() {
     assert_eq!(diff, single_max);
 }
 
+#[test]
+fn treemap_remove_big_range() {
+    let mut treemap = Treemap::new();
+    let value = 0xFFFFFFFFFFFF038D;
+    let range_end = 0xFFFFFFFFFF25FFFF;
+    treemap.add(value);
+
+    assert!(range_end < value);
+    treemap.remove_range(..value);
+    assert!(treemap.contains(value));
+    assert_eq!(treemap.cardinality(), 1);
+}
+
 #[test]
 fn treemap_run_optimized() {
     let mut initial = Bitmap::new();