added another prolog example

documents/Programmierparadigmen/scripts/scala/power-futures.scala

@@ -0,0 +1,57 @@
+import scala.actors.Futures._;
+
+object FastPower {
+    /**
+     * Calculate a power of two fast.
+     */
+    def fastPow(x: Int, n: Int): Long = {
+        var result = 1L;
+
+        val b = n.toBinaryString.reverse;
+        for(d <- 0 until b.length()) {
+            if(b.charAt(d).equals('1')){
+                result *= scala.math.pow(x,
+                    scala.math.pow(2, d)).toLong;
+            }
+        }
+
+        return result;
+    }
+
+    /**
+     * Calculate a power of two fast and use Futures.
+     */
+    def fastPowParallel(x: Int, n: Int): Long = {
+        var result = 1L;
+        val b = n.toBinaryString.reverse;
+        val tasks = for (d <- 0 until b.length())
+            yield future
+        {
+            var interim = 0L;
+            if (b.charAt(d).equals('1')){
+                interim = scala.math.pow(x,
+                    scala.math.pow(2, d)).toLong;
+            }
+
+            interim;
+        }
+
+        val futureRes = awaitAll(20000L, tasks: _*);
+
+        futureRes.foreach { res => 
+            res match {
+                case Some(x: Long) => if (x > 0) 
+                                        result *= x
+                case None => throw new
+                             Exception("error")
+            };
+        }
+
+        return result;
+    }
+
+    def main(args: Array[String]) {
+        println(fastPowParallel(2, 9));
+        // => 512
+    }
+}