Just another update

Task/Modular-exponentiation/D/modular-exponentiation.d

@@ -1,23 +1,30 @@
-import std.stdio, std.bigint;
+module modular_exponentiation;
 
-BigInt powMod(BigInt base, BigInt exponent, BigInt modulus)
-in {
+private import std.bigint;
+
+BigInt powMod(BigInt base, BigInt exponent, in BigInt modulus)
+pure nothrow /*@safe*/ in {
    assert(exponent >= 0);
 } body {
     BigInt result = 1;
-    while (exponent > 0) {
-        if (exponent % 2 == 1)
+
+    while (exponent) {
+        if (exponent & 1)
             result = (result * base) % modulus;
         exponent /= 2;
         base = base ^^ 2 % modulus;
     }
+
     return result;
 }
 
-void main() {
-    powMod(BigInt("29883481620585741369158914214988194" ~
-                  "66320163312926952423791023078876139"),
-           BigInt("235139930337346448646612254452369009" ~
-                  "4744975233415544072992656881240319"),
-           BigInt(10) ^^ 40).writeln();
-}
+version (modular_exponentiation)
+    void main() {
+        import std.stdio;
+
+        powMod(BigInt("29883481620585741369158914214988194" ~
+                      "66320163312926952423791023078876139"),
+               BigInt("235139930337346448646612254452369009" ~
+                      "4744975233415544072992656881240319"),
+               BigInt(10) ^^ 40).writeln;
+    }