Detect zero receiver of modInverse (may not converge and time out

runtime/lib/bigint.dart

 // Copyright (c) 2014, 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.
 
 // Copyright 2009 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
 /*
  * Copyright (c) 2003-2005  Tom Wu
@@ skipping 1524 matching lines @@
       }
     }
     assert(!is1);
     return z._revert(r_digits, r_used)._toValidInt();
   }
 
   // Returns 1/this % m, with m > 0.
   int modInverse(int m) {
     if (m is! int) throw new ArgumentError(m);
     if (m <= 0) throw new RangeError(m);
+    if (_used == 0) return 0;
     m = m._toBigint();
     // TODO(regis): Implement modInverse for an even modulus.
     if (m.isEven) throw new UnimplementedError();
     var t = this;
     if ((t._compare(m) >= 0) || t._neg) {
       t %= m;
       t = t._toBigint();
     }
     final t_used = t._used;
     if (t_used == 0) {
@@ skipping 352 matching lines @@
 
   int _mul(Uint32List x_digits, int x_used,
            Uint32List y_digits, int y_used,
            Uint32List r_digits) {
     var r_used = _Bigint._mulDigits(x_digits, x_used,
                                     y_digits, y_used,
                                     r_digits);
     return _reduce(r_digits, r_used);
   }
 }