Remove limit on bigint multiplication - fixes issue 12833.

tests/corelib/big_integer_vm_test.dart

 // Copyright (c) 2011, 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.
 // Testing Bigints.
 // TODO(srdjan): Make sure the numbers are Bigint and not Mint or Smi.
 
 library big_integer_test;
 import "package:expect/expect.dart";
 
 class BigIntegerTest {
@@ skipping 55 matching lines @@
     a = 12345678901234567890;
     b = 10000000000000000;
     Expect.equals(123456789012345678900000000000000000, a * b);
     // Bigint and double.
     a = 200.0;
     b = 100000000000;
     Expect.equals(20000000000000.0, a * b);
     Expect.equals(20000000000000.0, b * a);
   }
 
+  static testBigintHugeMul() {
+    var block = 28 * 256;   // 28 bit chunks with 8 bit 'carry' in a DoubleChunk.
+    var bits = block * 32;  // plenty of blocks in longest column sum;
+    var a = 1 << bits;
+    var a1 = a - 1;      // all 1's
+    var p1 = a1 * a1;
+    var p2 = a * a - a - a + 1;
+    // Use isTrue instead of equals to avoid trying to print such big numbers.
+    Expect.isTrue(p1 == p2, 'products do not match');
+  }
+
   static testBigintTruncDiv() {
     var a = 12345678901234567890;
     var b = 10;
     // Bigint and Smi.
     Expect.equals(1234567890123456789, a ~/ b);
     Expect.equals(0, b ~/ a);
     Expect.equals(123456789, 123456789012345678 ~/ 1000000000);
     // Bigint and Bigint.
     a = 12345678901234567890;
     b = 10000000000000000;
@@ skipping 67 matching lines @@
     }
     Expect.equals(true, exceptionCaught);
   }
 
   static testMain() {
     Expect.equals(1234567890123456789, foo());
     testSmiOverflow();
     testBigintAdd();
     testBigintSub();
     testBigintMul();
+    testBigintHugeMul();
     testBigintModulo();
     testBigintTruncDiv();
     testBigintDiv();
     testBigintNegate();
     testShiftAmount();
     Expect.equals(1234567890123456, (1234567890123456).abs());
     Expect.equals(1234567890123456, (-1234567890123456).abs());
     var a = 10000000000000000000;
     var b = 10000000000000000001;
     Expect.equals(false, a.hashCode == b.hashCode);
     Expect.equals(true, a.hashCode == (b - 1).hashCode);
   }
 }
 
 main() {
   BigIntegerTest.testMain();
 }