Int parsing with radix

parse_int

(*/!\ known bugs and shortcomings:
- lacks integer overflow check,
- lacks sign parsing (can't parse negative ints)
- exceptions are not helpfull
- code is ugly
- should benchmark parse_int against parse_int_
*)


let int_of_char c = match c with
  | '0' .. '9' -> Char.code c - Char.code '0'
  | 'a' .. 'z' -> Char.code c - Char.code 'a'
  | 'A' .. 'Z' -> Char.code c - Char.code 'A'
  | _ -> failwith "format error"

let rec parse_int_ i s a r =
  if i >= String.length s then
    a
  else
    let x = int_of_char s.[i] in
    if x >= r then
      failwith "format error"
    else
      parse_int_ (succ i) s ((r * a) + x) r


let parse_int s rdx = match rdx with
  | 2 -> int_of_string ("0b" ^ s)
  | 8 -> int_of_string ("0o" ^ s)
  | 10 -> int_of_string s
  | 16 -> int_of_string ("0b" ^ s)
  | r -> parse_int_ 0 s 0 r

let () = print_int (parse_int "444" 5)