gistfile1.ml

let base_default_alphabet = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ"
let base ?(alphabet=base_default_alphabet) n i =
  let rec aux a n sg i l =
    if i == 0
    then
      let l = if l = [] && n > 0 then [a.[0]] else l in
      let len = List.length l + if sg < 0 then 1 else 0 in
      let s = String.create len in
      if sg < 0 then s.[0] <- '-';
      let () = ignore (List.fold_right (fun i c -> s.[c-1] <- i; c-1) l len) in
      s
    else
      let quot = (i / n) in
      let rem = sg * (i - (quot*n)) in
      aux a n sg quot (a.[rem] :: l)
  in
  if String.length alphabet < n
    then invalid_arg (sprintf "Prelude.base: too short alphabet for base (%d, %S)" n alphabet);
  if n < 0
    then invalid_arg "Prelude.base: negative base is not allowed";
  let sg = if i < 0 then -1 else 1 in
  if n == 1 then
    let s = String.make (if sg < 0 then -i+1 else i) alphabet.[0] in
    let () = if sg < 0 then s.[0] <- '-' else () in
    s
  else aux alphabet n sg i []
(**T
  base 0 0 = ""
  optEx Division_by_zero (base 0) 47 = None
  base 1 45 = sreplicate 45 '0'
  base 1 0 = ""
  base 1 (-4) = "-0000"
  base 2 0 = "0"
  base 2 1 = "1"
  base 2 2 = "10"
  base 2 (-1) = "-1"
  base 2 (-2) = "-10"
  base 10 8489 = string_of_int 8489
  base 16 255 = "FF"
  base 16 (-255) = "-FF"
  base 16 (-1) = "-1"
  base ~alphabet:(lowercase base_default_alphabet) 16 255 = "ff"
  base 17 16 = "G"
  base 17 17 = "10"
  base 32 31 = "V"
  base 32 (-31) = "-V"
  base 32 32 = "10"

  optE (base 80) 92 = None
  optE (base (-1)) 73 = None
**)