Improve ScanJsonNumber.

src/conversions.cc

Index: src/conversions.cc
===================================================================
--- src/conversions.cc	(revision 6635)
+++ src/conversions.cc	(working copy)
@@ -702,26 +702,12 @@
 
 
 const char* DoubleToCString(double v, Vector<char> buffer) {
-  StringBuilder builder(buffer.start(), buffer.length());
-
   switch (fpclassify(v)) {
-    case FP_NAN:
-      builder.AddString("NaN");
-      break;
-
-    case FP_INFINITE:
-      if (v < 0.0) {
-        builder.AddString("-Infinity");
-      } else {
-        builder.AddString("Infinity");
-      }
-      break;
-
-    case FP_ZERO:
-      builder.AddCharacter('0');
-      break;
-
+    case FP_NAN: return "NaN";
+    case FP_INFINITE: return (v < 0.0 ? "-Infinity" : "Infinity");
+    case FP_ZERO: return "0";
     default: {
+      StringBuilder builder(buffer.start(), buffer.length());
       int decimal_point;
       int sign;
       const int kV8DtoaBufferCapacity = kBase10MaximalLength + 1;
@@ -764,9 +750,9 @@
         if (exponent < 0) exponent = -exponent;
         builder.AddFormatted("%d", exponent);
       }
+    return builder.Finalize();
     }
   }
-  return builder.Finalize();
 }