Add ceiling division operation to the Math.sol library (#2681)

Co-authored-by: Hadrien Croubois <hadrien.croubois@gmail.com>
Co-authored-by: Francisco Giordano <frangio.1@gmail.com>

test/utils/math/Math.test.js

@@ -1,6 +1,6 @@
-const { BN } = require('@openzeppelin/test-helpers');
-
+const { BN, constants } = require('@openzeppelin/test-helpers');
 const { expect } = require('chai');
+const { MAX_UINT256 } = constants;
 
 const MathMock = artifacts.require('MathMock');
 
@@ -55,4 +55,29 @@ contract('Math', function (accounts) {
       expect(await this.math.average(a, b)).to.be.bignumber.equal(bnAverage(a, b));
     });
   });
+
+  describe('ceilDiv', function () {
+    it('does not round up on exact division', async function () {
+      const a = new BN('10');
+      const b = new BN('5');
+      expect(await this.math.ceilDiv(a, b)).to.be.bignumber.equal('2');
+    });
+
+    it('rounds up on division with remainders', async function () {
+      const a = new BN('42');
+      const b = new BN('13');
+      expect(await this.math.ceilDiv(a, b)).to.be.bignumber.equal('4');
+    });
+
+    it('does not overflow', async function () {
+      const b = new BN('2');
+      const result = new BN('1').shln(255);
+      expect(await this.math.ceilDiv(MAX_UINT256, b)).to.be.bignumber.equal(result);
+    });
+
+    it('correctly computes max uint256 divided by 1', async function () {
+      const b = new BN('1');
+      expect(await this.math.ceilDiv(MAX_UINT256, b)).to.be.bignumber.equal(MAX_UINT256);
+    });
+  });
 });