From 6d97f0919547df11be9443b54af2d90631eaa733 Mon Sep 17 00:00:00 2001
From: rotcivegaf <victorfage@gmail.com>
Date: Sat, 10 Jul 2021 21:28:12 +0200
Subject: [PATCH] Gas optimization on average function of Math.sol (#2757)

* change implementation to save gas

* add average test with two max uni256 number
---
 contracts/utils/math/Math.sol | 4 ++--
 test/utils/math/Math.test.js  | 5 +++++
 2 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/contracts/utils/math/Math.sol b/contracts/utils/math/Math.sol
index 66bb22005..7280bddeb 100644
--- a/contracts/utils/math/Math.sol
+++ b/contracts/utils/math/Math.sol
@@ -25,8 +25,8 @@ library Math {
      * zero.
      */
     function average(uint256 a, uint256 b) internal pure returns (uint256) {
-        // (a + b) / 2 can overflow, so we distribute.
-        return (a / 2) + (b / 2) + (((a % 2) + (b % 2)) / 2);
+        // (a + b) / 2 can overflow.
+        return (a & b) + (a ^ b) / 2;
     }
 
     /**
diff --git a/test/utils/math/Math.test.js b/test/utils/math/Math.test.js
index 31d3e17ac..7e194dec7 100644
--- a/test/utils/math/Math.test.js
+++ b/test/utils/math/Math.test.js
@@ -54,6 +54,11 @@ contract('Math', function (accounts) {
       const b = new BN('84346');
       expect(await this.math.average(a, b)).to.be.bignumber.equal(bnAverage(a, b));
     });
+
+    it('is correctly calculated with two max uint256 numbers', async function () {
+      const a = MAX_UINT256;
+      expect(await this.math.average(a, a)).to.be.bignumber.equal(bnAverage(a, a));
+    });
   });
 
   describe('ceilDiv', function () {