lisp/hex-util.el

   1 ;;; hex-util.el --- Functions to encode/decode hexadecimal string -*- lexical-binding: t -*-
   2
   3 ;; Copyright (C) 1999, 2001-2017 Free Software Foundation, Inc.
   4
   5 ;; Author: Shuhei KOBAYASHI <shuhei@aqua.ocn.ne.jp>
   6 ;; Keywords: data
   7
   8 ;; This file is part of GNU Emacs.
   9
  10 ;; GNU Emacs is free software: you can redistribute it and/or modify
  11 ;; it under the terms of the GNU General Public License as published by
  12 ;; the Free Software Foundation, either version 3 of the License, or
  13 ;; (at your option) any later version.
  14
  15 ;; GNU Emacs is distributed in the hope that it will be useful,
  16 ;; but WITHOUT ANY WARRANTY; without even the implied warranty of
  17 ;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  18 ;; GNU General Public License for more details.
  19
  20 ;; You should have received a copy of the GNU General Public License
  21 ;; along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.
  22
  23 ;;; Commentary:
  24
  25 ;;; Code:
  26
  27 (eval-when-compile
  28   (defmacro hex-char-to-num (chr)
  29     `(let ((chr ,chr))
  30        (cond
  31         ((and (<= ?a chr)(<= chr ?f)) (+ (- chr ?a) 10))
  32         ((and (<= ?A chr)(<= chr ?F)) (+ (- chr ?A) 10))
  33         ((and (<= ?0 chr)(<= chr ?9)) (- chr ?0))
  34         (t (error "Invalid hexadecimal digit `%c'" chr)))))
  35   (defmacro num-to-hex-char (num)
  36     `(aref "0123456789abcdef" ,num)))
  37
  38 (defun decode-hex-string (string)
  39   "Decode hexadecimal STRING to octet string."
  40   (let* ((len (length string))
  41          (dst (make-string (/ len 2) 0))
  42          (idx 0)(pos 0))
  43     (while (< pos len)
  44       ;; logior and lsh are not byte-coded.
  45       ;; (aset dst idx (logior (lsh (hex-char-to-num (aref string pos)) 4)
  46       ;;                            (hex-char-to-num (aref string (1+ pos)))))
  47       (aset dst idx (+ (* (hex-char-to-num (aref string pos)) 16)
  48                        (hex-char-to-num (aref string (1+ pos)))))
  49       (setq idx (1+ idx)
  50             pos (+ 2 pos)))
  51     dst))
  52
  53 (defun encode-hex-string (string)
  54   "Encode octet STRING to hexadecimal string."
  55   (let* ((len (length string))
  56          (dst (make-string (* len 2) 0))
  57          (idx 0)(pos 0))
  58     (while (< pos len)
  59       ;; logand and lsh are not byte-coded.
  60       ;; (aset dst idx (num-to-hex-char (logand (lsh (aref string pos) -4) 15)))
  61       (aset dst idx (num-to-hex-char (/ (aref string pos) 16)))
  62       (setq idx (1+ idx))
  63       ;; (aset dst idx (num-to-hex-char (logand (aref string pos) 15)))
  64       (aset dst idx (num-to-hex-char (% (aref string pos) 16)))
  65       (setq idx (1+ idx)
  66             pos (1+ pos)))
  67     dst))
  68
  69 (provide 'hex-util)
  70
  71 ;;; hex-util.el ends here