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open StdLabels
type t = int
let column_of_char = function
| 'A' .. 'Z' as c -> Char.code c - (Char.code 'A' - 1)
| 'a' .. 'z' as c -> Char.code c - (Char.code 'a' - 1)
| c -> raise (Invalid_argument ("column: " ^ Char.escaped c))
let column_of_string : string -> int =
fun s ->
String.fold_left s ~init:0 ~f:(fun value c -> (value * 26) + column_of_char c)
(** Accumulate the remaining for the successives divisions in a list. *)
let rec _to_char ~b i =
if i > 0 then
let res = i mod 26 in
let res = if res = 0 then 26 else res in
let c = char_of_int @@ (res + 64) in
(* The modulo is accumulated in the list head, which is the expected
sequence *)
let b = c :: b in
_to_char ~b @@ ((i - res) / 26)
else b
let column_to_string i =
let res = _to_char ~b:[] i in
List.to_seq res |> String.of_seq
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