Just another update

Task/Fibonacci-sequence/Java/fibonacci-sequence-2.java

@@ -1,4 +1,28 @@
-public static long recFibN(final int n)
-{
- return (n < 2) ? n : recFibN(n - 1) + recFibN(n - 2);
+/**
+ * O(log(n))
+ */
+public static long fib(long n) {
+    if (n <= 0)
+	return 0;
+
+    long i = (int) (n - 1);
+    long a = 1, b = 0, c = 0, d = 1, tmp1,tmp2;
+
+    while (i > 0) {
+	if (i % 2 != 0) {
+            tmp1 = d * b + c * a;
+	    tmp2 = d * (b + a) + c * b;
+	    a = tmp1;
+	    b = tmp2;
+	}
+
+        tmp1 = (long) (Math.pow(c, 2) + Math.pow(d, 2));
+        tmp2 = d * (2 * c + d);
+			
+        c = tmp1;
+        d = tmp2;
+
+        i = i / 2;
+    }
+    return a + b;
 }