Check how many Smi digits are acceptable when parsing integers.

runtime/lib/integers_patch.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 // Dart core library.
 
 // VM implementation of int.
 
 patch class int {
 
   static bool _isWhitespace(int codePoint) {
     return
       (codePoint == 32) || // Space.
       ((9 <= codePoint) && (codePoint <= 13)); // CR, LF, TAB, etc.
   }
 
+  static bool is64Bit() => 1 << 32 is _Smi;
+
   static int _tryParseSmi(String str) {
     if (str.isEmpty) return null;
     var ix = 0;
     var endIx = str.length - 1;
     // Find first and last non-whitespace.
     while (ix <= endIx) {
       if (!_isWhitespace(str.codeUnitAt(ix))) break;
       ix++;
     }
     if (endIx < ix) {
       return null;  // Empty.
     }
     while (endIx > ix) {
       if (!_isWhitespace(str.codeUnitAt(endIx))) break;
       endIx--;
     }
 
     var isNegative = false;
     var c = str.codeUnitAt(ix);
     // Check for leading '+' or '-'.
     if ((c == 0x2b) || (c == 0x2d)) {
       ix++;
       isNegative = (c == 0x2d);
       if (ix > endIx) {
         return null;  // Empty.
       }
     }
-    if ((endIx - ix) >= 9) {
+    int smiLimit = is64Bit() ? 18 : 9;
+    if ((endIx - ix) >= smiLimit) {
       return null;  // May not fit into a Smi.
     }
     var result = 0;
     for (int i = ix; i <= endIx; i++) {
       var c = str.codeUnitAt(i) - 0x30;
       if ((c > 9) || (c < 0)) {
         return null;
       }
       result = result * 10 + c;
     }
@@ skipping 69 matching lines @@
       int digit = digits[code - 0x30];
       if (digit >= radix) return onError(source);
       result = result * radix + digit;
       i++;
       if (i == source.length) break;
       code = source.codeUnitAt(i);
     } while (true);
     return negative ? -result : result;
   }
 }