added getInterval() to MemoryBTree

Author: tomijaga

src/MemoryBTree/Base.mo

@@ -897,7 +897,7 @@ module {
         let (end_node, end_node_index) = Methods.get_leaf_node_by_index(btree, end);
 
         let start_index = start_node_index : Nat;
-        let end_index = end_node_index + 1 : Nat; // + 1 because the end index is exclusive
+        let end_index = end_node_index : Nat;
 
         RevIter.map<(Blob, Blob), (K, V)>(
             Methods.new_blobs_iterator(btree, start_node, start_index, end_node, end_index),
@@ -907,6 +907,20 @@ module {
         );
     };
 
+    public func getInterval<K, V>(btree : MemoryBTree, btree_utils : BTreeUtils<K, V>, start : ?K, end : ?K) : (Nat, Nat) {
+        let start_rank = switch (start) {
+            case (?key) getIndex(btree, btree_utils, key);
+            case (null) 0;
+        };
+
+        let end_rank = switch (end) {
+            case (?key) getIndex(btree, btree_utils, key) + 1; // +1 because the end is exclusive
+            case (null) btree.count;
+        };
+
+        (start_rank, end_rank);
+    };
+
     public func scan<K, V>(btree : MemoryBTree, btree_utils : BTreeUtils<K, V>, start : ?K, end : ?K) : RevIter<(K, V)> {
         let start_address = switch (start) {
             case (?key) {

src/MemoryBTree/lib.mo

@@ -125,6 +125,9 @@ module {
         /// Returns an array of all the values in the BTree
         public func toVals() : [V] = BaseMemoryBTree.toVals(state, btree_utils);
 
+        /// Returns the start and end index of the range between the given keys
+        public func getInterval(start : ?K, end : ?K) : (Nat, Nat) = BaseMemoryBTree.getInterval(state, btree_utils, start, end);
+
         /// Returns a reversible iterator over the entries in the given range
         public func range(i : Nat, j : Nat) : RevIter<(K, V)> = BaseMemoryBTree.range(state, btree_utils, i, j);