Source file versionCompare.ml

(******************************************************************************)
(* This file is part of the Dose library http://www.irill.org/software/dose *)
(* Copyright (C) 2011 Ralf Treinen <ralf.treinen@pps.jussieu.fr> *)
(* This library is free software: you can redistribute it and/or modify *)
(* it under the terms of the GNU Lesser General Public License as *)
(* published by the Free Software Foundation, either version 3 of the *)
(* License, or (at your option) any later version. A special linking *)
(* exception to the GNU Lesser General Public License applies to this *)
(* library, see the COPYING file for more information. *)
(* Work developed with the support of the Mancoosi Project *)
(* http://www.mancoosi.org *)
(******************************************************************************)

let is_digit = function '0'..'9' -> true | _ -> false

(* [skip_while_from i f w m] yields the index of the leftmost character
 * in the string [s], starting from [i], end ending at  [m], that does
 * not satisfy the predicate [f], or [length w] if no such index exists. *)
let skip_while_from i f w m =
  let rec loop i = if i = m then i else if f w.[i] then loop (i + 1) else i in
  loop i

(* splits a version into (epoch,rest), without the separating ':'. The
 * epoch is delimited by the leftmost occurrence of ':' in x, and is ""
 * in case there is no ':' in x. *)
let extract_epoch x =
  try
    let ci = String.index x ':' in
    let epoch = String.sub x 0 ci
    and rest = String.sub x (ci + 1) (String.length x - ci - 1) in
    (epoch, rest)
  with Not_found -> ("", x)

(* splits a version into (prefix,revision). The revision starts on the
 * right-most occurrence of '-', or is empty in case the version does
 * not contain '-'. *)
let extract_revision x =
  try
    let di = String.rindex x '-' in
    let before = String.sub x 0 di in
    let after = String.sub x (di + 1) (String.length x - di - 1) in
    (before, after)
  with Not_found -> (x, "")

(* character comparison uses a modified character ordering: '~' first, then
   letters, then anything else *)
let compare_chars c1 c2 =
  match c1 with
  | '~' -> ( match c2 with '~' -> 0 | _ -> -1 )
  | 'a'..'z' | 'A'..'Z' -> (
    match c2 with
    | '~' -> 1
    | 'a'..'z' | 'A'..'Z' -> Char.compare c1 c2
    | _ -> -1 )
  | _ ->
    match c2 with '~' | 'a'..'z' | 'A'..'Z' -> 1 | _ -> Char.compare c1 c2

(* return the first index of x, starting from xi, of a nun-null
 * character in x.  or (length x) in case x contains only 0's starting
 * from xi on. *)
let skip_zeros x xi xl = skip_while_from xi (fun c -> c = '0') x xl

(* compare versions chunks, that is parts of version strings that are
 * epoch, upstream version, or revisision. Alternates string comparison
 * and numerical comaprison. *)
let compare_chunks x y =
  (* x and y may be empty *)
  let xl = String.length x and yl = String.length y in
  let rec loop_lexical xi yi =
    assert (xi <= xl && yi <= yl) ;
    match (xi = xl, yi = yl) with
    (* which of x and y is exhausted? *)
    | true, true -> 0
    | true, false ->
        (* if y continues numerically than we have to continue by
         * comparing numerically. In this case the x part is
         * interpreted as 0 (since empty). If the y part consists
         * only of 0's then both parts are equal, otherwise the y
         * part is larger. If y continues non-numerically then y is
         * larger anyway, so we only have to skip 0's in the y part
         * and check whether this exhausts the y part. *)
        let ys = skip_zeros y yi yl in
        if ys = yl then 0 else if y.[ys] = '~' then 1 else -1
    | false, true ->
        (* symmetric to the preceding case *)
        let xs = skip_zeros x xi xl in
        if xs = xl then 0 else if x.[xs] = '~' then -1 else 1
    | false, false ->
      (* which of x and y continues numerically? *)
      match (is_digit x.[xi], is_digit y.[yi]) with
      | true, true ->
          (* both continue numerically. Skip leading zeros in the * remaining
             parts, and then continue by * comparing numerically. *)
          compare_numerical (skip_zeros x xi xl) (skip_zeros y yi yl)
      | true, false ->
          (* '~' is smaller than any numeric part *)
          if y.[yi] = '~' then 1 else -1
      | false, true ->
          (* '~' is smaller than any numeric part *)
          if x.[xi] = '~' then -1 else 1
      | false, false ->
          (* continue comparing lexically *)
          let comp = compare_chars x.[xi] y.[yi] in
          if comp = 0 then loop_lexical (xi + 1) (yi + 1) else comp
  and compare_numerical xi yi =
    assert (xi = xl || (xi < xl && x.[xi] <> '0')) ;
    (* leading zeros have been stripped *)
    assert (yi = yl || (yi < yl && y.[yi] <> '0')) ;
    (* leading zeros have been stripped *)
    let xn = skip_while_from xi is_digit x xl
    (* length of numerical part *)
    and yn = skip_while_from yi is_digit y yl (* length of numerical part *) in
    let comp = compare (xn - xi) (yn - yi) in
    if comp = 0 then
      (* both numerical parts have same length: compare digit by digit *)
      loop_numerical xi yi yn
    else
      (* if one numerical part is longer than the other we have found the *
         answer since leading 0 have been striped when switching * to numerical
         comparison. *)
      comp
  and loop_numerical xi yi yn =
    assert (xi <= xl && yi <= yn && yn <= yl) ;
    (* invariant: the two numerical parts that remain to compare are of the
       same length *)
    if yi = yn then
      (* both numerical parts are exhausted, we switch to lexical comparison *)
      loop_lexical xi yi
    else
      (* both numerical parts are not exhausted, we continue comparing digit by
         digit *)
      let comp = Char.compare x.[xi] y.[yi] in
      if comp = 0 then loop_numerical (xi + 1) (yi + 1) yn else comp
  in
  loop_lexical 0 0

let compare (x: string) (y: string) =
  let normalize_comp_result x = if x = 0 then 0 else if x < 0 then -1 else 1 in
  if x = y then 0
  else
    let e1, rest1 = extract_epoch x and e2, rest2 = extract_epoch y in
    let e_comp = compare_chunks e1 e2 in
    if e_comp <> 0 then normalize_comp_result e_comp
    else
      let u1, r1 = extract_revision rest1
      and u2, r2 = extract_revision rest2 in
      let u_comp = compare_chunks u1 u2 in
      if u_comp <> 0 then normalize_comp_result u_comp
      else normalize_comp_result (compare_chunks r1 r2)

let equal (x: string) (y: string) = if x = y then true else compare x y = 0