langs a-z

Task/Fibonacci-sequence/PowerShell/fibonacci-sequence-1.psh

@@ -0,0 +1,26 @@
+function fib ($n) {
+    if ($n -eq 0) { return 0 }
+    if ($n -eq 1) { return 1 }
+
+    $m = 1
+    if ($n -lt 0) {
+        if ($n % 2 -eq -1) {
+            $m = 1
+        } else {
+            $m = -1
+        }
+
+        $n = -$n
+    }
+
+    $a = 0
+    $b = 1
+
+    for ($i = 1; $i -lt $n; $i++) {
+        $c = $a + $b
+        $a = $b
+        $b = $c
+    }
+
+    return $m * $b
+}