From 56515380452baad9fcd32c5d4502002af0183ce9 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Nicol=C3=A1s=20Venturo?= <nicolas.venturo@gmail.com>
Date: Mon, 4 Jun 2018 20:04:08 -0300
Subject: [PATCH] Clarified the rationaly behind the mul branch test. (#970)

---
 contracts/math/SafeMath.sol | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/contracts/math/SafeMath.sol b/contracts/math/SafeMath.sol
index c603c7558..3b8d75905 100644
--- a/contracts/math/SafeMath.sol
+++ b/contracts/math/SafeMath.sol
@@ -11,9 +11,13 @@ library SafeMath {
   * @dev Multiplies two numbers, throws on overflow.
   */
   function mul(uint256 a, uint256 b) internal pure returns (uint256 c) {
+    // Gas optimization: this is cheaper than asserting 'a' not being zero, but the
+    // benefit is lost if 'b' is also tested.
+    // See: https://github.com/OpenZeppelin/openzeppelin-solidity/pull/522
     if (a == 0) {
       return 0;
     }
+
     c = a * b;
     assert(c / a == b);
     return c;