From d93a6d62981ee901948187ee1a52bbc61dac5ae1 Mon Sep 17 00:00:00 2001
From: poma <semenov.roma@gmail.com>
Date: Tue, 24 Aug 2021 19:19:26 +0300
Subject: [PATCH] Use switcher from circomlib

---
 circuits/merkleTree.circom  | 46 +++++++++----------------------------
 circuits/treeUpdater.circom |  8 +++----
 2 files changed, 15 insertions(+), 39 deletions(-)

diff --git a/circuits/merkleTree.circom b/circuits/merkleTree.circom
index 302c0d7..feeacb0 100644
--- a/circuits/merkleTree.circom
+++ b/circuits/merkleTree.circom
@@ -1,28 +1,5 @@
 include "../node_modules/circomlib/circuits/poseidon.circom";
-
-// Computes MiMC([left, right])
-template HashLeftRight() {
-    signal input left;
-    signal input right;
-    signal output hash;
-
-    component hasher = Poseidon(2);
-    hasher.inputs[0] <== left;
-    hasher.inputs[1] <== right;
-    hash <== hasher.out;
-}
-
-// if s == 0 returns [in[0], in[1]]
-// if s == 1 returns [in[1], in[0]]
-template DualMux() {
-    signal input in[2];
-    signal input s;
-    signal output out[2];
-
-    s * (1 - s) === 0
-    out[0] <== (in[1] - in[0])*s + in[0];
-    out[1] <== (in[0] - in[1])*s + in[1];
-}
+include "../node_modules/circomlib/circuits/switcher.circom";
 
 // Verifies that merkle proof is correct for given merkle root and a leaf
 // pathIndices input is an array of 0/1 selectors telling whether given pathElement is on the left or right side of merkle path
@@ -30,25 +7,24 @@ template MerkleTree(levels) {
     signal input leaf;
     signal input pathElements[levels];
     signal input pathIndices;
-
     signal output root;
 
-    component selectors[levels];
-    component hashers[levels];
+    component switcher[levels];
+    component hasher[levels];
 
     component indexBits = Num2Bits(levels);
     indexBits.in <== pathIndices;
 
     for (var i = 0; i < levels; i++) {
-        selectors[i] = DualMux();
-        selectors[i].in[0] <== i == 0 ? leaf : hashers[i - 1].hash;
-        selectors[i].in[1] <== pathElements[i];
-        selectors[i].s <== indexBits.out[i];
+        switcher[i] = Switcher();
+        switcher[i].L <== i == 0 ? leaf : hasher[i - 1].out;
+        switcher[i].R <== pathElements[i];
+        switcher[i].sel <== indexBits.out[i];
 
-        hashers[i] = HashLeftRight();
-        hashers[i].left <== selectors[i].out[0];
-        hashers[i].right <== selectors[i].out[1];
+        hasher[i] = Poseidon(2);
+        hasher[i].inputs[0] <== switcher[i].outL;
+        hasher[i].inputs[1] <== switcher[i].outR;
     }
 
-    root <== hashers[levels - 1].hash;
+    root <== hasher[levels - 1].out;
 }
diff --git a/circuits/treeUpdater.circom b/circuits/treeUpdater.circom
index c77ae7a..6495a1e 100644
--- a/circuits/treeUpdater.circom
+++ b/circuits/treeUpdater.circom
@@ -17,9 +17,9 @@ template TreeUpdater(levels, subtreeLevels, zeroSubtreeRoot) {
     // calculate subtree root
     // todo: make it work with arbitrary subtree levels
     // currently it works only with 1-level subtrees
-    component leafPair = HashLeftRight();
-    leafPair.left <== leaf[0];
-    leafPair.right <== leaf[1];
+    component leafPair = Poseidon(2);
+    leafPair.inputs[0] <== leaf[0];
+    leafPair.inputs[1] <== leaf[1];
 
     component treeBefore = MerkleTree(remainingLevels);
     for(var i = 0; i < remainingLevels; i++) {
@@ -34,6 +34,6 @@ template TreeUpdater(levels, subtreeLevels, zeroSubtreeRoot) {
         treeAfter.pathElements[i] <== pathElements[i];
     }
     treeAfter.pathIndices <== pathIndices;
-    treeAfter.leaf <== leafPair.hash;
+    treeAfter.leaf <== leafPair.out;
     treeAfter.root === newRoot;
 }