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;;; china-util.el --- utilities for Chinese -*- lexical-binding: t; -*-
;; Copyright (C) 1995, 2001-2025 Free Software Foundation, Inc.
;; Copyright (C) 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004,
;; 2005, 2006, 2007, 2008, 2009, 2010, 2011
;; National Institute of Advanced Industrial Science and Technology (AIST)
;; Registration Number H14PRO021
;; Copyright (C) 2003
;; National Institute of Advanced Industrial Science and Technology (AIST)
;; Registration Number H13PRO009
;; Keywords: mule, multilingual, Chinese
;; This file is part of GNU Emacs.
;; GNU Emacs is free software: you can redistribute it and/or modify
;; it under the terms of the GNU General Public License as published by
;; the Free Software Foundation, either version 3 of the License, or
;; (at your option) any later version.
;; GNU Emacs 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 General Public License for more details.
;; You should have received a copy of the GNU General Public License
;; along with GNU Emacs. If not, see <https://www.gnu.org/licenses/>.
;;; Commentary:
;;; Code:
;; Hz/ZW/EUC-TW encoding stuff
;; HZ is an encoding method for Chinese character set GB2312 used
;; widely in Internet. It is very similar to 7-bit environment of
;; ISO-2022. The difference is that HZ uses the sequence "~{" and
;; "~}" for designating GB2312 and ASCII respectively, hence, it
;; doesn't uses ESC (0x1B) code.
;; ZW is another encoding method for Chinese character set GB2312. It
;; encodes Chinese characters line by line by starting each line with
;; the sequence "zW". It also uses only 7-bit as HZ.
;; EUC-TW is similar to EUC-KS or EUC-JP. Its main character set is
;; plane 1 of CNS 11643; characters of planes 2 to 7 are accessed with
;; a single shift escape followed by three bytes: the first gives the
;; plane, the second and third the character code. Note that characters
;; of plane 1 are (redundantly) accessible with a single shift escape
;; also.
;; ISO-2022 escape sequence to designate GB2312.
(defvar iso2022-gb-designation "\e$A")
;; HZ escape sequence to designate GB2312.
(defvar hz-gb-designation "~{")
;; ISO-2022 escape sequence to designate ASCII.
(defvar iso2022-ascii-designation "\e(B")
;; HZ escape sequence to designate ASCII.
(defvar hz-ascii-designation "~}")
;; Regexp of ZW sequence to start GB2312.
(defvar zw-start-gb "^zW")
;; Regexp for start of GB2312 in an encoding mixture of HZ and ZW.
(defvar hz/zw-start-gb
(concat hz-gb-designation "\\|" zw-start-gb "\\|[^\0-\177]"))
(defvar decode-hz-line-continuation nil
"Flag to tell if we should care line continuation convention of Hz.")
(defconst hz-set-msb-table
(eval-when-compile
(let ((chars nil)
(i 0))
(while (< i 33)
(push i chars)
(setq i (1+ i)))
(while (< i 127)
(push (decode-char 'eight-bit (+ i 128)) chars)
(setq i (1+ i)))
(apply 'string (nreverse chars)))))
;;;###autoload
(defun decode-hz-region (beg end)
"Decode HZ/ZW encoded text in the current region.
Return the length of resulting text."
(interactive "r")
(save-excursion
(save-restriction
(let (pos ch)
(narrow-to-region beg end)
;; We, at first, convert HZ/ZW to `iso-2022-7bit',
;; then decode it.
;; "~\n" -> "", "~~" -> "~"
(goto-char (point-min))
(while (search-forward "~" nil t)
(setq ch (following-char))
(cond ((= ch ?{)
(delete-region (1- (point)) (1+ (point)))
(setq pos (point))
(insert iso2022-gb-designation)
(if (looking-at "\\([!-}][!-~]\\)*")
(goto-char (match-end 0)))
(if (looking-at hz-ascii-designation)
(delete-region (match-beginning 0) (match-end 0)))
(insert iso2022-ascii-designation)
(decode-coding-region pos (point) 'iso-2022-7bit))
((= ch ?~)
(delete-char 1))
((and (= ch ?\n)
decode-hz-line-continuation)
(delete-region (1- (point)) (1+ (point))))
(t
(forward-char 1)))))
(- (point-max) (point-min)))))
;;;###autoload
(defun decode-hz-buffer ()
"Decode HZ/ZW encoded text in the current buffer."
(interactive)
(decode-hz-region (point-min) (point-max)))
(defvar hz-category-table nil)
;;;###autoload
(defun encode-hz-region (beg end)
"Encode the text in the current region to HZ.
Return the length of resulting text."
(interactive "r")
(unless hz-category-table
(setq hz-category-table (make-category-table))
(with-category-table hz-category-table
(define-category ?c "hz encodable")
(map-charset-chars #'modify-category-entry 'ascii ?c)
(map-charset-chars #'modify-category-entry 'chinese-gb2312 ?c)))
(save-excursion
(save-restriction
(narrow-to-region beg end)
(with-category-table hz-category-table
;; ~ -> ~~
(goto-char (point-min))
(while (search-forward "~" nil t) (insert ?~))
;; ESC -> ESC ESC
(goto-char (point-min))
(while (search-forward "\e" nil t) (insert ?\e))
;; Non-ASCII-GB2312 -> \uXXXX
(goto-char (point-min))
(while (re-search-forward "\\Cc" nil t)
(let ((ch (preceding-char)))
(delete-char -1)
(insert (format (if (< ch #x10000) "\\u%04X" "\\U%08X") ch))))
;; Prefer chinese-gb2312 for Chinese characters.
(put-text-property (point-min) (point-max) 'charset 'chinese-gb2312)
(encode-coding-region (point-min) (point-max) 'iso-2022-7bit)
;; ESC $ B ... ESC ( B -> ~{ ... ~}
;; ESC ESC -> ESC
(goto-char (point-min))
(while (search-forward "\e" nil t)
(if (= (following-char) ?\e)
;; ESC ESC -> ESC
(delete-char 1)
(forward-char -1)
(if (looking-at "\e\\$A")
(progn
(delete-region (match-beginning 0) (match-end 0))
(insert hz-gb-designation)
(search-forward iso2022-ascii-designation nil 'move)
(delete-region (match-beginning 0) (match-end 0))
(insert hz-ascii-designation))))))
(- (point-max) (point-min)))))
;;;###autoload
(defun encode-hz-buffer ()
"Encode the text in the current buffer to HZ."
(interactive)
(encode-hz-region (point-min) (point-max)))
;;;###autoload
(defun post-read-decode-hz (len)
(let ((pos (point))
(buffer-modified-p (buffer-modified-p))
last-coding-system-used)
(prog1
(decode-hz-region pos (+ pos len))
(set-buffer-modified-p buffer-modified-p))))
;;;###autoload
(defun pre-write-encode-hz (from to)
(let ((buf (current-buffer)))
(set-buffer (generate-new-buffer " *temp*"))
(if (stringp from)
(insert from)
(insert-buffer-substring buf from to))
(let (last-coding-system-used)
(encode-hz-region 1 (point-max)))
nil))
;;
(provide 'china-util)
;;; china-util.el ends here
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