lisp/hex-util.el

   1 ;;; hex-util.el --- Functions to encode/decode hexadecimal string.
   2
   3 ;; Copyright (C) 1999, 2001, 2002, 2003, 2004,
   4 ;;   2005, 2006, 2007, 2008, 2009, 2010 Free Software Foundation, Inc.
   5
   6 ;; Author: Shuhei KOBAYASHI <shuhei@aqua.ocn.ne.jp>
   7 ;; Keywords: data
   8
   9 ;; This file is part of GNU Emacs.
  10
  11 ;; GNU Emacs is free software: you can redistribute it and/or modify
  12 ;; it under the terms of the GNU General Public License as published by
  13 ;; the Free Software Foundation, either version 3 of the License, or
  14 ;; (at your option) any later version.
  15
  16 ;; GNU Emacs is distributed in the hope that it will be useful,
  17 ;; but WITHOUT ANY WARRANTY; without even the implied warranty of
  18 ;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  19 ;; GNU General Public License for more details.
  20
  21 ;; You should have received a copy of the GNU General Public License
  22 ;; along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.
  23
  24 ;;; Commentary:
  25
  26 ;;; Code:
  27
  28 (eval-when-compile
  29   (defmacro hex-char-to-num (chr)
  30     `(let ((chr ,chr))
  31        (cond
  32         ((and (<= ?a chr)(<= chr ?f)) (+ (- chr ?a) 10))
  33         ((and (<= ?A chr)(<= chr ?F)) (+ (- chr ?A) 10))
  34         ((and (<= ?0 chr)(<= chr ?9)) (- chr ?0))
  35         (t (error "Invalid hexadecimal digit `%c'" chr)))))
  36   (defmacro num-to-hex-char (num)
  37     `(aref "0123456789abcdef" ,num)))
  38
  39 (defun decode-hex-string (string)
  40   "Decode hexadecimal STRING to octet string."
  41   (let* ((len (length string))
  42          (dst (make-string (/ len 2) 0))
  43          (idx 0)(pos 0))
  44     (while (< pos len)
  45       ;; logior and lsh are not byte-coded.
  46       ;; (aset dst idx (logior (lsh (hex-char-to-num (aref string pos)) 4)
  47       ;;                            (hex-char-to-num (aref string (1+ pos)))))
  48       (aset dst idx (+ (* (hex-char-to-num (aref string pos)) 16)
  49                        (hex-char-to-num (aref string (1+ pos)))))
  50       (setq idx (1+ idx)
  51             pos (+ 2 pos)))
  52     dst))
  53
  54 (defun encode-hex-string (string)
  55   "Encode octet STRING to hexadecimal string."
  56   (let* ((len (length string))
  57          (dst (make-string (* len 2) 0))
  58          (idx 0)(pos 0))
  59     (while (< pos len)
  60       ;; logand and lsh are not byte-coded.
  61       ;; (aset dst idx (num-to-hex-char (logand (lsh (aref string pos) -4) 15)))
  62       (aset dst idx (num-to-hex-char (/ (aref string pos) 16)))
  63       (setq idx (1+ idx))
  64       ;; (aset dst idx (num-to-hex-char (logand (aref string pos) 15)))
  65       (aset dst idx (num-to-hex-char (% (aref string pos) 16)))
  66       (setq idx (1+ idx)
  67             pos (1+ pos)))
  68     dst))
  69
  70 (provide 'hex-util)
  71
  72 ;;; hex-util.el ends here