efficient bulk insert

.prettierrc

@@ -0,0 +1,7 @@
+{
+  "semi": false,
+  "arrowParens": "always",
+  "singleQuote": true,
+  "printWidth": 110,
+  "trailingComma": "all"
+}

package.json

@@ -1,7 +1,8 @@
 {
   "name": "fixed-merkle-tree",
-  "version": "0.4.0",
+  "version": "0.6.0",
   "description": "Fixed depth merkle tree implementation with sequential inserts",
+  "repository": "https://github.com/tornadocash/fixed-merkle-tree.git",
   "main": "src/merkleTree.js",
   "scripts": {
     "test": "mocha",

src/merkleTree.js

@@ -22,22 +22,21 @@ class MerkleTree {
    * @param {hashFunction} [options.hashFunction] Function used to hash 2 leaves
    * @param [options.zeroElement] Value for non-existent leaves
    */
-  constructor(levels, elements = [], { hashFunction, zeroElement = DEFAULT_ZERO } = {}) {
+  constructor(levels, elements = [], { hashFunction = defaultHash, zeroElement = DEFAULT_ZERO } = {}) {
     this.levels = levels
-    this.capacity = 1 << levels
-    this.zeroElement = zeroElement
-    this._hash = hashFunction || defaultHash
+    this.capacity = 2 ** levels
     if (elements.length > this.capacity) {
       throw new Error('Tree is full')
     }
-
+    this._hash = hashFunction
+    this.zeroElement = zeroElement
     this._zeros = []
-    this._layers = []
-    this._layers[0] = elements
-    this._zeros[0] = this.zeroElement
+    this._zeros[0] = zeroElement
     for (let i = 1; i <= levels; i++) {
       this._zeros[i] = this._hash(this._zeros[i - 1], this._zeros[i - 1])
     }
+    this._layers = []
+    this._layers[0] = elements.slice()
     this._rebuild()
   }
 
@@ -47,9 +46,9 @@ class MerkleTree {
       for (let i = 0; i < Math.ceil(this._layers[level - 1].length / 2); i++) {
         this._layers[level][i] = this._hash(
           this._layers[level - 1][i * 2],
-          i * 2 + 1 < this._layers[level - 1].length ?
-            this._layers[level - 1][i * 2 + 1] :
-            this._zeros[level - 1],
+          i * 2 + 1 < this._layers[level - 1].length
+            ? this._layers[level - 1][i * 2 + 1]
+            : this._zeros[level - 1],
         )
       }
     }
@@ -75,15 +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])
   }
 
   /**
@@ -100,9 +114,9 @@ class MerkleTree {
       index >>= 1
       this._layers[level][index] = this._hash(
         this._layers[level - 1][index * 2],
-        index * 2 + 1 < this._layers[level - 1].length ?
-          this._layers[level - 1][index * 2 + 1] :
-          this._zeros[level - 1],
+        index * 2 + 1 < this._layers[level - 1].length
+          ? this._layers[level - 1][index * 2 + 1]
+          : this._zeros[level - 1],
       )
     }
   }
@@ -120,9 +134,8 @@ class MerkleTree {
     const pathIndices = []
     for (let level = 0; level < this.levels; level++) {
       pathIndices[level] = index % 2
-      pathElements[level] = (index ^ 1) < this._layers[level].length ?
-        this._layers[level][index ^ 1] :
-        this._zeros[level]
+      pathElements[level] =
+        (index ^ 1) < this._layers[level].length ? this._layers[level][index ^ 1] : this._zeros[level]
       index >>= 1
     }
     return {
@@ -153,6 +166,14 @@ class MerkleTree {
     return this._layers[0].slice()
   }
 
+  /**
+   * Returns a copy of n-th zero elements array
+   * @returns {Object[]}
+   */
+  zeros() {
+    return this._zeros.slice()
+  }
+
   /**
    * Serialize entire tree state including intermediate layers into a plain object
    * Deserializing it back will not require to recompute any hashes
@@ -161,8 +182,6 @@ class MerkleTree {
   serialize() {
     return {
       levels: this.levels,
-      capacity: this.capacity,
-      zeroElement: this.zeroElement,
       _zeros: this._zeros,
       _layers: this._layers,
     }
@@ -180,6 +199,8 @@ class MerkleTree {
   static deserialize(data, hashFunction) {
     const instance = Object.assign(Object.create(this.prototype), data)
     instance._hash = hashFunction || defaultHash
+    instance.capacity = 2 ** instance.levels
+    instance.zeroElement = instance._zeros[0]
     return instance
   }
 }

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])