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

runtime/lib/integers.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.
 
 // TODO(srdjan): fix limitations.
 // - shift amount must be a Smi.
 class _IntegerImplementation extends _Num {
   // The Dart class _Bigint extending _IntegerImplementation requires a
   // default constructor.
 
@@ skipping 247 matching lines @@
     var mask = radix - 1;
     do {
       string._setAt(--length, _digits.codeUnitAt(value & mask));
       value >>= bitsPerDigit;
     } while (value > 0);
     return string;
   }
 
   _leftShiftWithMask32(count, mask)  native "Integer_leftShiftWithMask32";
 
-  // Return pow(this, e) % m.
+  // Returns pow(this, e) % m.
   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;
     if (e is _Bigint || m is _Bigint) {
       return _toBigint().modPow(e, m);
     }
     if (e < 1) return 1;
     int b = this;
     if (b < 0 || b > m) {
-      b = b % m;
+      b %= m;
     }
     int r = 1;
     while (e > 0) {
-     if ((e & 1) != 0) {
-       r = (r * b) % m;
-     }
-     e >>= 1;
-     b = (b * b) % m;
+      if (e.isOdd) {
+        r = (r * b) % m;
+      }
+      e >>= 1;
+      b = (b * b) % m;
     }
     return r;
   }
 }
 
 class _Smi extends _IntegerImplementation implements int {
   factory _Smi._uninstantiable() {
     throw new UnsupportedError(
         "_Smi can only be allocated by the VM");
   }
@@ skipping 204 matching lines @@
   // Shift by mint exceeds range that can be handled by the VM.
   int _shrFromInt(int other) {
     if (other < 0) {
       return -1;
     } else {
       return 0;
     }
   }
   int _shlFromInt(int other) native "Mint_shlFromInt";
 }