feat(mod): Add mod function (#86) (#87)

Closes #86

Author: tbarber350

src/index.js

@@ -27,6 +27,7 @@ import dec2bin from './dec2bin'
 import searchAndReplace from './search-and-replace'
 import sqrt from './sqrt'
 import toPower from './to-power'
+import mod from './mod'
 
 export {
   initArray,
@@ -57,4 +58,5 @@ export {
   searchAndReplace,
   sqrt,
   toPower,
+  mod,
 }

src/mod.js

@@ -0,0 +1,16 @@
+export default mod
+
+/**
+ * Original Source: http://stackoverflow.com/a/17323608
+ *
+ * This method provides a modulo function that will always return a positive
+ * value even when supplied a negative dividend.
+ *
+ * @param {Number} dividend - the number to be divided by divisor
+ * @param {Number} divisor - the number divided by
+ * @returns {Number} - the remainder
+ */
+
+function mod(dividend, divisor) {
+  return ((dividend % divisor) + divisor) % divisor
+}

test/mod.test.js

@@ -0,0 +1,18 @@
+import test from 'ava'
+import {mod} from '../src'
+
+test('a dividend larger than divisor', t => {
+  const dividend = 12
+  const divisor = 8
+  const expected = 4
+  const result = mod(dividend, divisor)
+  t.is(expected, result)
+})
+
+test('a negative dividend', t => {
+  const dividend = -12
+  const divisor = 8
+  const expected = 4
+  const result = mod(dividend, divisor)
+  t.is(expected, result)
+})