From dd27a0adc7566319e231836fcf1aed5d4e495f57 Mon Sep 17 00:00:00 2001
From: Tejo Kumar Reddy Chenchu <tejo.kumar.reddy.chenchu@sap.com>
Date: Thu, 24 Sep 2015 01:12:13 -0700
Subject: [PATCH] Fix rounding issue with the `precision` param of `_.floor`.

---
 lodash.js    | 11 +++++++++--
 test/test.js | 38 ++++++++++++++++++++++++++++----------
 2 files changed, 37 insertions(+), 12 deletions(-)

diff --git a/lodash.js b/lodash.js
index 5888858c9..876cdae18 100644
--- a/lodash.js
+++ b/lodash.js
@@ -4081,8 +4081,15 @@
       return function(number, precision) {
         precision = precision ? toInteger(precision) : 0;
         if (precision) {
-          precision = pow(10, precision);
-          return func(number * precision) / precision;
+          // Shift the decimal point with exponential notation to avoid floating-point funny bussiness.
+          // See [MDN](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Math/round#Examples)
+          // for more details.
+          var pair = (+number + 'e').split('e'),
+              value = func(pair[0] + 'e' + (+pair[1] + precision));
+
+          // Shift back.
+          pair = (value + 'e').split('e');
+          return +(pair[0] + 'e' + (pair[1] - precision));
         }
         return func(number);
       };
diff --git a/test/test.js b/test/test.js
index 364e18117..d6d1ea59c 100644
--- a/test/test.js
+++ b/test/test.js
@@ -11362,6 +11362,7 @@
       }
     });
   }());
+
   /*--------------------------------------------------------------------------*/
 
   QUnit.module('lodash.mapKeys');
@@ -16222,13 +16223,30 @@
       assert.strictEqual(actual, isCeil ? 5 : 4);
     });
 
-    QUnit.test('`_.' + methodName + '` should return a rounded number with a precision of `0`', function(assert) {
+    QUnit.test('`_.' + methodName + '` should work with a precision of `0`', function(assert) {
       assert.expect(1);
 
       var actual = func(4.006, 0);
       assert.strictEqual(actual, isCeil ? 5 : 4);
     });
 
+    QUnit.test('`_.' + methodName + '` should work with a positive precision', function(assert) {
+      assert.expect(2);
+
+      var actual = func(4.016, 2);
+      assert.strictEqual(actual, isFloor ? 4.01 : 4.02);
+
+      actual = func(4.1, 2);
+      assert.strictEqual(actual, 4.1);
+    });
+
+    QUnit.test('`_.' + methodName + '` should work with a negative precision', function(assert) {
+      assert.expect(1);
+
+      var actual = func(4160, -2);
+      assert.strictEqual(actual, isFloor ? 4100 : 4200);
+    });
+
     QUnit.test('`_.' + methodName + '` should coerce `precision` to an integer', function(assert) {
       assert.expect(3);
 
@@ -16244,18 +16262,18 @@
       assert.strictEqual(actual, expected);
     });
 
-    QUnit.test('`_.' + methodName + '` should return a rounded number with a positive precision', function(assert) {
-      assert.expect(1);
+    QUnit.test('`_.' + methodName + '` should work with exponential notation and `precision`', function(assert) {
+      assert.expect(3);
 
-      var actual = func(4.016, 2);
-      assert.strictEqual(actual, isFloor ? 4.01 : 4.02);
-    });
+      var actual = func(5e1, 2);
+      assert.deepEqual(actual, 50);
 
-    QUnit.test('`_.' + methodName + '` should return a rounded number with a negative precision', function(assert) {
-      assert.expect(1);
+      actual = func('5e', 1);
+      assert.deepEqual(actual, NaN);
+
+      actual = func('5e1e1', 1);
+      assert.deepEqual(actual, NaN);
 
-      var actual = func(4160, -2);
-      assert.strictEqual(actual, isFloor ? 4100 : 4200);
     });
   });