Frog: Fix parsing of hex literals with >31 bits

frog/parser.dart

Index: frog/parser.dart
diff --git a/frog/parser.dart b/frog/parser.dart
index 18fa60ff73d15052e918aedb681f70d43dbc4caa..4d321dacf044d52ca55b39cb4ee75b62c42457e2 100644
--- a/frog/parser.dart
+++ b/frog/parser.dart
@@ -1334,10 +1334,14 @@ class Parser {
   static int parseHex(String hex) {
     var result = 0;
 
-    for (int i=0; i < hex.length; i++) {
+    for (int i = 0; i < hex.length; i++) {
       var digit = _hexDigit(hex.charCodeAt(i));
       assert(digit != -1);
-      result = (result << 4) + digit;
+      // Multiply by 16 rather than shift by 4 since that will result in a
+      // correct value for numbers that exceed the 32 bit precision of JS
+      // 'integers'.
+      // TODO: Figure out a better solution to integer truncation. Issue 638.
+      result = (result * 16) + digit;
     }
 
     return result;