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compare-w.el
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1993-07-23
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;;; compare-w.el --- compare text between windows for Emacs.
;; Copyright (C) 1986, 1989, 1993 Free Software Foundation, Inc.
;; Maintainer: FSF
;; 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 2, 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.
;;; Commentary:
;; This package provides one entry point, compare-windows. It compares
;; text starting from point in two adjacent windows, advancing point
;; until it finds a difference. Option variables permit you to ignore
;; whitespace differences, or case differences, or both.
;;; Code:
(defvar compare-windows-whitespace "[ \t\n]+"
"*Regexp that defines whitespace sequences for \\[compare-windows].
Changes in whitespace are optionally ignored.
The value of `compare-windows-whitespace' may instead be a function; this
function is called in each buffer, with point at the current scanning point.
The function's job is to categorize any whitespace around (including before)
point; it should also advance past any whitespace.
The function is passed one argument, the point where `compare-windows'
was originally called; it should not consider any text before that point.
If the function returns the same value for both buffers, then the
whitespace is considered to match, and is skipped.")
(defvar compare-ignore-case nil
"*Non-nil means \\[compare-windows] ignores case differences.")
;;;###autoload
(defun compare-windows (ignore-whitespace)
"Compare text in current window with text in next window.
Compares the text starting at point in each window,
moving over text in each one as far as they match.
A prefix arg means ignore changes in whitespace.
The variable `compare-windows-whitespace' controls how whitespace is skipped.
If `compare-ignore-case' is non-nil, changes in case are also ignored."
(interactive "P")
(let* (p1 p2 maxp1 maxp2 b1 b2 w2
success size
(opoint1 (point))
opoint2
(skip-whitespace (if ignore-whitespace
compare-windows-whitespace)))
(setq p1 (point) b1 (current-buffer))
(setq w2 (next-window (selected-window)))
(if (eq w2 (selected-window))
(error "No other window"))
(setq p2 (window-point w2)
b2 (window-buffer w2))
(setq opoint2 p2)
(setq maxp1 (point-max))
(save-excursion
(set-buffer b2)
(setq maxp2 (point-max)))
(setq success t)
(while success
(setq success nil)
;; if interrupted, show how far we've gotten
(goto-char p1)
(set-window-point w2 p2)
;; If both buffers have whitespace next to point,
;; optionally skip over it.
(and skip-whitespace
(save-excursion
(let (p1a p2a w1 w2 result1 result2)
(setq result1
(if (stringp skip-whitespace)
(compare-windows-skip-whitespace opoint1)
(funcall skip-whitespace opoint1)))
(setq p1a (point))
(set-buffer b2)
(goto-char p2)
(setq result2
(if (stringp skip-whitespace)
(compare-windows-skip-whitespace opoint2)
(funcall skip-whitespace opoint2)))
(setq p2a (point))
(and result1 result2 (eq result1 result2)
(setq p1 p1a
p2 p2a)))))
;; Try advancing comparing 1000 chars at a time.
;; When that fails, go 500 chars at a time, and so on.
(let ((size 1000)
success-1
(case-fold-search compare-ignore-case))
(while (> size 0)
(setq success-1 t)
;; Try comparing SIZE chars at a time, repeatedly, till that fails.
(while success-1
(setq size (min size (- maxp1 p1) (- maxp2 p2)))
(setq success-1
(and (> size 0)
(= 0 (compare-buffer-substrings b2 p2 (+ size p2)
b1 p1 (+ size p1)))))
(if success-1
(setq p1 (+ p1 size) p2 (+ p2 size)
success t)))
;; If SIZE chars don't match, try fewer.
(setq size (/ size 2)))))
(goto-char p1)
(set-window-point w2 p2)
(if (= (point) opoint1)
(ding))))
;; Move forward over whatever might be called whitespace.
;; compare-windows-whitespace is a regexp that matches whitespace.
;; Match it at various starting points before the original point
;; and find the latest point at which a match ends.
;; Don't try starting points before START, though.
;; Value is non-nil if whitespace is found.
(defun compare-windows-skip-whitespace (start)
(let ((end (point))
(opoint (point)))
(while (and (looking-at compare-windows-whitespace)
(<= end (match-end 0))
;; This match goes past END, so advance END.
(progn (setq end (match-end 0))
(> (point) start)))
;; keep going back until whitespace
;; doesn't extend to or past end
(forward-char -1))
(goto-char end)
(/= end opoint)))
(provide 'compare-w)
;;; compare-w.el ends here