Times different methods for calculating the number of digits of an integer.

calc_digits.ml

#load "unix.cma";;
open Printf;;

let by_string x =
	x |> string_of_int |> String.length
;;

let rec by_recursion = function
	| 0 -> 1
	| x -> 1 + by_recursion (x / 10)
;;

let by_loop x =
	let x' = ref x in
	let digits = ref 0 in
	while !x' > 0 do
		digits := !digits + 1;
		x' := !x' / 10;
		if !x' == 0 then digits := !digits + 1
	done;
	!digits
;;

let by_log x =
	x |> float_of_int |> log10 |> floor |> (+.) 1. |> int_of_float
;;

let test_method times name func =
	let rec test func = function
		| 0 -> ()
		| x -> func x; test func (x - 1)
	in

	let start = Unix.gettimeofday () in
	printf "Testing %s method with %d...\n" name times;
	test func times;
	let stop = Unix.gettimeofday () in
	printf "...finished in %.8f seconds\n" (stop -. start);
;;

let main () =
	let test = test_method 100_000_000 in
	test "string" by_string;
	test "recursion" by_recursion;
	test "loop" by_loop;
	test "log" by_log;
;;

main ();