perf(imt): when updating a node, skip calculation if value is the same (

#350)

In order to improve performance, we can avoid recalculating the Incremental Merkel Tree in the event
that the update value is the same as the tree value.

re #340

packages/imt/src/imt.ts

@@ -224,6 +224,8 @@ export default class IMT {
             throw new Error("The leaf does not exist in this tree")
         }
 
+        if (newLeaf === this._nodes[0][index]) return
+
         let node = newLeaf
 
         for (let level = 0; level < this.depth; level += 1) {

packages/imt/tests/imt.test.ts

@@ -131,6 +131,25 @@ describe("IMT", () => {
                         expect(tree.root).toEqual(root)
                     }
                 })
+
+                it(`Should not error when update value is the same`, () => {
+                    for (let i = 0; i < numberOfLeaves; i += 1) {
+                        tree.insert(1)
+                        oldTree.insert(1)
+                    }
+
+                    const previousRoot = tree.root
+
+                    for (let i = 0; i < numberOfLeaves; i += 1) {
+                        tree.update(i, 1)
+                        oldTree.update(i, 1)
+
+                        const { root } = oldTree.genMerklePath(0)
+
+                        expect(tree.root).toEqual(root)
+                        expect(tree.root).toEqual(previousRoot)
+                    }
+                })
             })
 
             describe("# indexOf", () => {