4.4BSD/usr/src/contrib/emacs-18.57/lisp/tabify.el

;; Tab conversion commands for Emacs
;; Copyright (C) 1985 Free Software Foundation, Inc.

;; 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 1, 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; see the file COPYING.  If not, write to
;; the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.


(defun untabify (start end)
  "Convert all tabs in region to multiple spaces, preserving columns.
The variable tab-width controls the action."
  (interactive "r")
  (save-excursion
    (save-restriction
      (narrow-to-region start end)
      (goto-char start)
      (while (search-forward "\t" nil t)	; faster than re-search
	(let ((start (point))
	      (column (current-column))
	      (indent-tabs-mode nil))
	  (skip-chars-backward "\t")
	  (delete-region start (point))
	  (indent-to column))))))

(defun tabify (start end)
  "Convert multiple spaces in region to tabs when possible.
A group of spaces is partially replaced by tabs
when this can be done without changing the column they end at.
The variable tab-width controls the action."
  (interactive "r")
  (save-excursion
    (save-restriction
      (narrow-to-region start end)
      (goto-char start)
      (while (re-search-forward "[ \t][ \t][ \t]*" nil t)
	(let ((column (current-column))
	      (indent-tabs-mode t))
	  (delete-region (match-beginning 0) (point))
	  (indent-to column))))))