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(* Js_of_ocaml compiler
* http://www.ocsigen.org/js_of_ocaml/
* Copyright (C) 2013 Hugo Heuzard
*
* This program 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, with linking exception;
* either version 2.1 of the License, or (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
*)
open! Stdlib
let alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/="
let code_rev =
let a = Array.make 256 (-1) in
for i = 0 to String.length alphabet - 1 do
a.(Char.code alphabet.[i]) <- i
done;
a
let in_alphabet x = code_rev.(Char.code x) <> -1
let vlq_base_shift = 5
(* binary: 100000 *)
let vlq_base = 1 lsl vlq_base_shift
(* binary: 011111 *)
let vlq_base_mask = vlq_base - 1
(* binary: 100000 *)
let vlq_continuation_bit = vlq_base
let toVLQSigned v = if v < 0 then (-v lsl 1) + 1 else v lsl 1
(* assert (toVLQSigned 1 = 2); *)
(* assert (toVLQSigned 2 = 4); *)
(* assert (toVLQSigned (-1) = 3); *)
(* assert (toVLQSigned (-2) = 5);; *)
let fromVLQSigned v =
let is_neg = v land 1 = 1 in
let shift = v lsr 1 in
if is_neg then -shift else shift
(* assert (fromVLQSigned 2 = 1); *)
(* assert (fromVLQSigned 4 = 2); *)
(* assert (fromVLQSigned 3 = -1); *)
(* assert (fromVLQSigned 5 = -2);; *)
let add_char buf x = Buffer.add_char buf alphabet.[x]
let rec encode' buf x =
let digit = x land vlq_base_mask in
let rest = x lsr vlq_base_shift in
if rest = 0
then add_char buf digit
else (
add_char buf (digit lor vlq_continuation_bit);
encode' buf rest)
let encode b x =
let vql = toVLQSigned x in
encode' b vql
let encode_l b l = List.iter ~f:(encode b) l
let rec decode' acc s start pos =
let digit = code_rev.(Char.code s.[pos]) in
if digit = -1 then invalid_arg "Vql64.decode'";
let cont = digit land vlq_continuation_bit = vlq_continuation_bit in
let digit = digit land vlq_base_mask in
let acc = acc + (digit lsl ((pos - start) * vlq_base_shift)) in
if cont then decode' acc s start (succ pos) else acc, succ pos
let decode s p =
let d, i = decode' 0 s p p in
fromVLQSigned d, i
let decode_l s ~pos ~len =
let rec aux pos acc len =
if len = 0
then List.rev acc
else if len < 0
then invalid_arg "Vlq64.decode_l"
else
let d, i = decode s pos in
let len = len - (i - pos) in
aux i (d :: acc) len
in
aux pos [] len
type input =
{ string : string
; mutable pos : int
; len : int
}
let rec decode' src s pos len offset i =
if pos = len then invalid_arg "Vql64.decode'";
let digit = Array.unsafe_get code_rev (Char.code s.[pos]) in
if digit = -1 then invalid_arg "Vql64.decode'";
let i = i + ((digit land vlq_base_mask) lsl offset) in
if digit >= vlq_continuation_bit
then decode' src s (pos + 1) len (offset + vlq_base_shift) i
else (
src.pos <- pos + 1;
i)
let decode src = fromVLQSigned (decode' src src.string src.pos src.len 0 0)
|
