add fibonacci implementations to integration tests

Signed-off-by: xermicus <cyrill@parity.io>

crates/integration/contracts/Fibonacci.sol

@@ -0,0 +1,62 @@
+// Source:
+// https://medium.com/coinmonks/fibonacci-in-solidity-8477d907e22a
+
+contract FibonacciRecursive {
+    function f(uint n) internal pure returns (uint) {
+        if (n <= 1) {
+            return n;
+        } else {
+            return f(n - 1) + f(n - 2);
+        }
+    }
+
+    function fib3(uint n) public pure returns (uint) {
+        return f(n);
+    }
+}
+
+contract FibonacciIterative {
+    function fib3(uint n) external pure returns (uint b) {
+        if (n == 0) {
+            return 0;
+        }
+        uint a = 1;
+        b = 1;
+        for (uint i = 2; i < n; i++) {
+            uint c = a + b;
+            a = b;
+            b = c;
+        }
+        return b;
+    }
+}
+
+contract FibonacciBinet {
+    function fib3(uint n) external pure returns (uint a) {
+        if (n == 0) {
+            return 0;
+        }
+        uint h = n / 2;
+        uint mask = 1;
+        // find highest set bit in n
+        while (mask <= h) {
+            mask <<= 1;
+        }
+        mask >>= 1;
+        a = 1;
+        uint b = 1;
+        uint c;
+        while (mask > 0) {
+            c = a * a + b * b;
+            if (n & mask > 0) {
+                b = b * (b + 2 * a);
+                a = c;
+            } else {
+                a = a * (2 * b - a);
+                b = c;
+            }
+            mask >>= 1;
+        }
+        return a;
+    }
+}