examples_in_progress/bigInt/parse.ml

   1
   2 open BigInt__N
   3
   4 exception SyntaxError
   5
   6 let times10 a =
   7   let a2 = add a a in
   8   let a4 = add a2 a2 in
   9   let a5 = add a4 a in
  10   add a5 a5
  11
  12 let parse_dec s idx =
  13   let a = ref (from_small_int 0) in
  14   let i = ref idx in
  15   try
  16   while !i < String.length s do
  17     match String.get s !i with
  18       | '0'..'9' as c ->
  19         let d = Char.code c - Char.code '0' in
  20         a := add (times10 !a) (from_small_int d);
  21         i := succ !i
  22       | _ ->
  23         raise Exit
  24   done;
  25   raise Exit
  26   with Exit ->
  27     if !i = idx then raise SyntaxError else !a,!i
  28
  29 let parse_sep_star s idx =
  30   let i = ref idx in
  31   try
  32   while !i < String.length s do
  33     match String.get s !i with
  34       | ' ' | '\t' | '\n' | '\r' -> i := succ !i
  35       | _ -> raise Exit
  36   done;
  37   raise Exit
  38   with Exit -> !i
  39
  40 open Format
  41
  42 let pr fmt a =
  43   let a = a.digits in
  44   let l = Array.length a in
  45   fprintf fmt "%d" a.(l-1);
  46   for i=l-2 downto 0 do
  47     fprintf fmt "%04d" a.(i);
  48   done
  49