Add modPow(int exponent, int modulus) method to int abstract class.

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 1320 matching lines @@
   int _remainderFromInteger(int other) {
     return other._toBigint()._rem(this)._toValidInt();
   }
   bool _greaterThanFromInteger(int other) {
     return other._toBigint()._compare(this) > 0;
   }
   bool _equalToInteger(int other) {
     return other._toBigint()._compare(this) == 0;
   }
 
-  // Return pow(this, e) % m, with e >= 0, m > 0.
+  // Returns pow(this, e) % m, with e >= 0, m > 0.
   int modPow(int e, int m) {
-    if (e is! int || e < 0) throw new ArgumentError(e);
-    if (m is! int || m <= 0) throw new ArgumentError(m);
+    if (e is! int) throw new ArgumentError(e);
+    if (m is! int) throw new ArgumentError(m);
+    if (e < 0) throw new RangeError(e);
+    if (m <= 0) throw new RangeError(m);
+    if (e == 0) return 1;
     final m_used = m._used;
     final m_used2p2 = 2*m_used + 1 + 1;  // +1 for leading zero.
     final e_bitlen = e.bitLength;
     if (e_bitlen <= 0) return 1;
     if ((e is! _Bigint) || m.isEven) {
       _Reduction z = (e_bitlen < 8 || m.isEven) ?
           new _Classic(m) : new _Montgomery(m);
       // TODO(regis): Should we use Barrett reduction for an even modulus?
       var m_used = m._used;
       var r_digits = new Uint32List(m_used2p2);
@@ skipping 383 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);
   }
 }