efficient bulk insert

(cherry picked from commit c83a4a4dc0e97338c2dbb83236dffb577dea73fa)

src/merkleTree.js

@@ -74,15 +74,30 @@ class MerkleTree {
   }
 
   /**
-   * Insert multiple elements into the tree. Tree will be fully rebuilt during this operation.
+   * Insert multiple elements into the tree.
    * @param {Array} elements Elements to insert
    */
   bulkInsert(elements) {
     if (this._layers[0].length + elements.length > this.capacity) {
       throw new Error('Tree is full')
     }
-    this._layers[0].push(...elements)
-    this._rebuild()
+    // First we insert all elements except the last one
+    // updating only full subtree hashes (all layers where inserted element has odd index)
+    // the last element will update the full path to the root making the tree consistent again
+    for (let i = 0; i < elements.length - 1; i++) {
+      this._layers[0].push(elements[i])
+      let level = 0
+      let index = this._layers[0].length - 1
+      while (index % 2 === 1) {
+        level++
+        index >>= 1
+        this._layers[level][index] = this._hash(
+          this._layers[level - 1][index * 2],
+          this._layers[level - 1][index * 2 + 1],
+        )
+      }
+    }
+    this.insert(elements[elements.length - 1])
   }
 
   /**

test/merkleTree.test.js

@@ -71,6 +71,32 @@ describe('MerkleTree', () => {
       tree.root().should.equal('10132905325673518287563057607527946096399700874345297651940963130460267058606')
     })
 
+    it('should give the same result as sequental inserts', () => {
+      const initialArray = [
+        [1],
+        [1, 2],
+        [1, 2, 3],
+        [1, 2, 3, 4],
+      ]
+      const insertedArray = [
+        [11],
+        [11, 12],
+        [11, 12, 13],
+        [11, 12, 13, 14],
+      ]
+      for (const initial of initialArray) {
+        for (const inserted of insertedArray) {
+          const tree1 = new MerkleTree(10, initial)
+          const tree2 = new MerkleTree(10, initial)
+          tree1.bulkInsert(inserted)
+          for (const item of inserted) {
+            tree2.insert(item)
+          }
+          tree1.root().should.equal(tree2.root())
+        }
+      }
+    }).timeout(10000)
+
     it('should work with max elements', () => {
       const tree = new MerkleTree(2, [1, 2])
       tree.bulkInsert([3, 4])