fix(currency): Handle not-quite-zero values

IEEE 754 floating point sometimes results in values that are very small,
rather than zero. One example is 1.0 + 1.07 - 2.07, which returns
4.440892098500626e-16 instead of 0.

This change tweaks the number formatting logic so that an exponential
value with a negative exponent that is larger than the precision+1
returns 0 instead. For example: with precision 2, anything with an
exponent of -4, -5 or more would become 0. 9e-3 = 0.009 = 0.01, but 9e-4
= 0.0009 = 0.001 = 0.00. This detail is unlikely to matter since this
quirk is usually only triggered with values very close to zero.

Closes #1469

2 files changed, 18 insertions, 2 deletions

diff --git a/src/ng/filter/filters.js b/src/ng/filter/filters.js
index 376afd85..57186981 100644
--- a/src/ng/filter/filters.js
+++ b/src/ng/filter/filters.js
@@ -117,9 +117,18 @@ function formatNumber(number, pattern, groupSep, decimalSep, fractionSize) {
       formatedText = '',
       parts = [];
 
+  var hasExponent = false;
   if (numStr.indexOf('e') !== -1) {
-    formatedText = numStr;
-  } else {
+    var match = numStr.match(/([\d\.]+)e(-?)(\d+)/);
+    if (match && match[2] == '-' && match[3] > fractionSize + 1) {
+      numStr = '0';
+    } else {
+      formatedText = numStr;
+      hasExponent = true;
+    }
+  }
+
+  if (!hasExponent) {
     var fractionLen = (numStr.split(DECIMAL_SEP)[1] || '').length;
 
     // determine fractionSize if it is not specified
diff --git a/test/ng/filter/filtersSpec.js b/test/ng/filter/filtersSpec.js
index 883e91f6..cbb41841 100644
--- a/test/ng/filter/filtersSpec.js
+++ b/test/ng/filter/filtersSpec.js
@@ -91,6 +91,13 @@ describe('filters', function() {
       expect(currency()).toBe('');
       expect(currency('abc')).toBe('');
     });
+
+    it('should handle zero and nearly-zero values properly', function() {
+      // This expression is known to yield 4.440892098500626e-16 instead of 0.0.
+      expect(currency(1.07 + 1 - 2.07)).toBe('$0.00');
+      expect(currency(0.008)).toBe('$0.01');
+      expect(currency(0.003)).toBe('$0.00');
+    });
   });