From 9aa30e19605e686d324448645c6594d2d31464c6 Mon Sep 17 00:00:00 2001
From: jeano <33420400+JeanoLee@users.noreply.github.com>
Date: Tue, 14 Aug 2018 05:40:48 +0900
Subject: [PATCH] Add Modulo operation for getting the quotient (#915)

* Add Modulo operation for getting the quotient

* Improved modulo tests and implementation.

* Removed assertion.
---
 contracts/math/SafeMath.sol      |  9 +++++++
 contracts/mocks/SafeMathMock.sol |  4 ++++
 test/math/SafeMath.test.js       | 40 ++++++++++++++++++++++++++++++++
 3 files changed, 53 insertions(+)

diff --git a/contracts/math/SafeMath.sol b/contracts/math/SafeMath.sol
index e978fc42899..da591c3b207 100644
--- a/contracts/math/SafeMath.sol
+++ b/contracts/math/SafeMath.sol
@@ -54,4 +54,13 @@ library SafeMath {
 
     return c;
   }
+
+  /**
+  * @dev Divides two numbers and returns the remainder (unsigned integer modulo),
+  * reverts when dividing by zero.
+  */
+  function mod(uint256 a, uint256 b) internal pure returns (uint256) {
+    require(b != 0);
+    return a % b;
+  }
 }
diff --git a/contracts/mocks/SafeMathMock.sol b/contracts/mocks/SafeMathMock.sol
index df749b5ac22..d69d6e5cc3d 100644
--- a/contracts/mocks/SafeMathMock.sol
+++ b/contracts/mocks/SafeMathMock.sol
@@ -21,4 +21,8 @@ contract SafeMathMock {
   function add(uint256 _a, uint256 _b) public pure returns (uint256) {
     return SafeMath.add(_a, _b);
   }
+
+  function mod(uint256 a, uint256 b) public pure returns (uint256) {
+    return SafeMath.mod(a, b);
+  }
 }
diff --git a/test/math/SafeMath.test.js b/test/math/SafeMath.test.js
index 2c0018c184e..3a96e2609ee 100644
--- a/test/math/SafeMath.test.js
+++ b/test/math/SafeMath.test.js
@@ -1,4 +1,5 @@
 const { assertRevert } = require('../helpers/assertRevert');
+
 const BigNumber = web3.BigNumber;
 const SafeMathMock = artifacts.require('SafeMathMock');
 
@@ -88,4 +89,43 @@ contract('SafeMath', () => {
       await assertRevert(this.safeMath.div(a, b));
     });
   });
+
+  describe('mod', function () {
+    describe('modulos correctly', async function () {
+      it('when the dividend is smaller than the divisor', async function () {
+        const a = new BigNumber(284);
+        const b = new BigNumber(5678);
+
+        (await this.safeMath.mod(a, b)).should.be.bignumber.equal(a.mod(b));
+      });
+
+      it('when the dividend is equal to the divisor', async function () {
+        const a = new BigNumber(5678);
+        const b = new BigNumber(5678);
+
+        (await this.safeMath.mod(a, b)).should.be.bignumber.equal(a.mod(b));
+      });
+
+      it('when the dividend is larger than the divisor', async function () {
+        const a = new BigNumber(7000);
+        const b = new BigNumber(5678);
+
+        (await this.safeMath.mod(a, b)).should.be.bignumber.equal(a.mod(b));
+      });
+
+      it('when the dividend is a multiple of the divisor', async function () {
+        const a = new BigNumber(17034); // 17034 == 5678 * 3
+        const b = new BigNumber(5678);
+
+        (await this.safeMath.mod(a, b)).should.be.bignumber.equal(a.mod(b));
+      });
+    });
+
+    it('reverts with a 0 divisor', async function () {
+      const a = new BigNumber(5678);
+      const b = new BigNumber(0);
+
+      await assertRevert(this.safeMath.mod(a, b));
+    });
+  });
 });