let inline fastPow x (n:int) =
   if n < 1 then failwith "Parameter n must be greater then 0"
   else
   new System.Collections.BitArray([|n|]) 
                |> Seq.cast<bool>                     //cast bit array to bool array
                |> Seq.rev                           
                |> Seq.skipWhile (fun b -> not b)     //skip leading false bits 
                |> Seq.skip 1                                       //skip one true bit
                |> Seq.fold (
                     fun a b -> 
                                let sq = a*a
                                if b then   //if true bit
                                  printfn "square and mul (2 ops)"
                                  sq * x             //squaring and then multiplying  
                                else        //if false bit
                                  printfn "just square (1 op)"
                                  sq                 //only squaring
                     ) x
//test
fastPow 3 11
fastPow 1.3 16
fastPow (new System.Numerics.Complex(1.1,1.02)) 17
fastPow 15I 16
//function narrowed to float type
//let floatPow x n:float = if n = 0 then 1.0 elif n<0 then 1.0 / (fastPow x (-n)) else fastPow x n