let rec loop i =
let t1 = Unix.gettimeofday () in
let r = f x in
let t2 = Unix.gettimeofday () in
let t = (1000. *. (t2 -. t1)) in
let rec loop i =
let t1 = Unix.gettimeofday () in
let r = f x in
let t2 = Unix.gettimeofday () in
let t = (1000. *. (t2 -. t1)) in