-Fixed JsonReader.ReadAsDouble with a JValue BigInteger

Src/Newtonsoft.Json.Tests/Linq/JTokenReaderTest.cs

@@ -51,6 +51,20 @@ namespace Newtonsoft.Json.Tests.Linq
     [TestFixture]
     public class JTokenReaderTest : TestFixtureBase
     {
+#if !(NET20 || NET35 || PORTABLE40 || PORTABLE)
+        [Test]
+        public void ConvertBigIntegerToDouble()
+        {
+            var jObject = JObject.Parse("{ maxValue:10000000000000000000}");
+
+            JsonReader reader = jObject.CreateReader();
+            Assert.IsTrue(reader.Read());
+            Assert.IsTrue(reader.Read());
+            Assert.AreEqual(10000000000000000000d, reader.ReadAsDouble());
+            Assert.IsTrue(reader.Read());
+        }
+#endif
+
         [Test]
         public void ErrorTokenIndex()
         {

Src/Newtonsoft.Json/JsonReader.cs

@@ -622,12 +622,24 @@ namespace Newtonsoft.Json
                 case JsonToken.Float:
                     if (!(Value is double))
                     {
-                        SetToken(JsonToken.Float, Convert.ToDouble(Value, CultureInfo.InvariantCulture), false);
+                        double d;
+#if !(NET20 || NET35 || PORTABLE40 || PORTABLE)
+                        if (Value is BigInteger)
+                        {
+                            d = (double)(BigInteger)Value;
+                        }
+                        else
+#endif
+                        {
+                            d = Convert.ToDouble(Value, CultureInfo.InvariantCulture);
+                        }
+
+                        SetToken(JsonToken.Float, d, false);
                     }
 
-                    return (double) Value;
+                    return (double)Value;
                 case JsonToken.String:
-                    return ReadDoubleString((string) Value);
+                    return ReadDoubleString((string)Value);
             }
 
             throw JsonReaderException.Create(this, "Error reading double. Unexpected token: {0}.".FormatWith(CultureInfo.InvariantCulture, t));