gistfile1.txt

let base = Char.code '0'
let rec string_of_int_rec b i n =
  let i = i - 1 in
  Bytes.unsafe_set b i (Char.unsafe_chr (base + n mod 10));
  let n = n / 10 in
  if n = 0 then i
  else string_of_int_rec b i n

let int_min_str = string_of_int min_int

let string_of_int2 n =
  let len = 20 in
  let b = Bytes.create len in
  if n < 0 then
    if n = min_int then int_min_str
    else
      let pos = string_of_int_rec b len (-n) - 1 in
      Bytes.unsafe_set b pos '-';
      Bytes.sub_string b pos (len - pos)
  else
    let pos = string_of_int_rec b len n in
    Bytes.sub_string b pos (len - pos)

let tst = [min_int; min_int+1;-10;-1;0;1;10;max_int-1;max_int]
let () =
  tst |> List.iter @@ fun i ->
  assert (string_of_int i = string_of_int i)

let () =
  for _ = 1 to 10_000_000 do
    ignore @@ Sys.opaque_identity (string_of_int2 0)
  done