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+;;; -*- Mode: Emacs-lisp -*-
+;; Copyright (C) 1991 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.
+
+;;; Written by Michael D. Ernst, mernst@theory.lcs.mit.edu, 1/26/91
+
+;;; Reposition-window makes an entire function definition or comment visible,
+;;; or, if it is already visible, places it at the top of the window;
+;;; additional invocations toggle the visibility of comments preceding the
+;;; code.  For the gory details, see the documentation for reposition-window;
+;;; rather than reading that, you may just want to play with it.
+
+;;; The recommended binding for this function is M-C-r:
+;;;  (global-set-key "\e\C-r" 'reposition-window)
+
+;;; This tries pretty hard to do the recentering correctly; the precise
+;;; action depends on what the buffer looks like.  If you find a situation
+;;; where it doesn't behave well, let me know.  This function is modeled
+;;; after one of the same name in ZMACS, but the code is all-new and the
+;;; behavior in some situations differs.
+
+(defun reposition-window (&optional arg)
+  "Make the current definition and/or comment visible.
+Further invocations move it to the top of the window or toggle the
+visibility of comments that precede it.
+  Point is left unchanged unless prefix ARG is supplied.
+  If the definition is fully onscreen, it is moved to the top of the
+window.  If it is partly offscreen, the window is scrolled to get the
+definition (or as much as will fit) onscreen, unless point is in a comment
+which is also partly offscreen, in which case the scrolling attempts to get
+as much of the comment onscreen as possible.
+  Initially `reposition-window' attempts to make both the definition and
+preceding comments visible.  Further invocations toggle the visibility of
+the comment lines.
+  If ARG is non-nil, point may move in order to make the whole defun
+visible (if only part could otherwise be made so), to make the defun line
+visible (if point is in code and it could not be made so, or if only
+comments, including the first comment line, are visible), or to make the
+first comment line visible (if point is in a comment)."
+  (interactive "P")
+  (let* (;; (here (save-excursion (beginning-of-line) (point)))
+         (here (point))
+         ;; change this name once I've gotten rid of references to ht.
+         ;; this is actually the number of the last screen line
+         (ht (- (window-height (selected-window)) 2))
+         (line (repos-count-screen-lines (window-start) (point)))
+         (comment-height
+          ;; The call to max deals with the case of cursor between defuns.
+          (max 0
+               (repos-count-screen-lines-signed
+                ;; the beginning of the preceding comment
+                (save-excursion
+                  (forward-char 1) (end-of-defun -1) 
+                  ;; Skip whitespace, newlines, and form feeds.
+                  (re-search-forward "[^\\s \n\014]")
+                  (backward-char 1)
+                  (point))
+                here)))
+         (defun-height 
+           (repos-count-screen-lines-signed
+            (save-excursion
+              (end-of-defun 1) ; so comments associate with following defuns
+              (beginning-of-defun 1)
+              (point))
+            here))
+         ;; This must be positive, so don't use the signed version.
+         (defun-depth (repos-count-screen-lines here
+                                                (save-excursion
+                                                  (end-of-defun 1)
+                                                  (point))))
+         (defun-line-onscreen-p
+           (and (<= defun-height line)
+                (<= (- line defun-height) ht))))
+    (cond ((or (= comment-height line)
+               (and (= line ht)
+                    (> comment-height line)
+                    ;; if defun line offscreen, we should be in case 4
+                    defun-line-onscreen-p))
+           ;; Either first comment line is at top of screen or (point at
+           ;; bottom of screen, defun line onscreen, and first comment line
+           ;; off top of screen).  That is, it looks like we just did
+           ;; recenter-definition, trying to fit as much of the comment
+           ;; onscreen as possible.  Put defun line at top of screen; that
+           ;; is, show as much code, and as few comments, as possible.
+
+           (if (and arg (> defun-depth (1+ ht)))
+               ;; Can't fit whole defun onscreen without moving point.
+               (progn (end-of-defun) (beginning-of-defun) (recenter 0))
+             (recenter (max defun-height 0)))
+           ;;(repos-debug-macro "1")
+           )
+
+          ((or (= defun-height line)
+               (= line 0)
+               (and (< line comment-height)
+                    (< defun-height 0)))
+           ;; Defun line or cursor at top of screen, OR cursor in comment
+           ;; whose first line is offscreen.
+           ;; Avoid moving definition up even if defun runs offscreen;
+           ;; we care more about getting the comment onscreen.
+           
+           (cond ((= line ht)
+                  ;; cursor on last screen line (and so in a comment)
+                  (if arg (progn (end-of-defun) (beginning-of-defun)))
+                  (recenter 0)
+                  ;;(repos-debug-macro "2a")
+                  )
+                 
+                 ;; This condition, copied from case 4, may not be quite right
+                 
+                 ((and arg (< ht comment-height))
+                  ;; Can't get first comment line onscreen.
+                  ;; Go there and try again.
+                  (forward-line (- comment-height))
+                  (beginning-of-line)
+                  ;; was (reposition-window)
+                  (recenter 0)
+                  ;;(repos-debug-macro "2b")
+                  )
+                 (t
+                  (recenter (min ht comment-height))
+                  ;;(repos-debug-macro "2c")
+                  ))
+           ;; (recenter (min ht comment-height))
+           )
+
+          ((and (> (+ line defun-depth -1) ht)
+                defun-line-onscreen-p)
+           ;; Defun runs off the bottom of the screen and the defun line
+           ;; is onscreen.
+           ;; Move the defun up.
+           (recenter (max 0 (1+ (- ht defun-depth)) defun-height))
+           ;;(repos-debug-macro "3")
+           )
+
+          (t
+           ;; If on the bottom line and comment start is offscreen
+           ;; then just move all comments offscreen, or at least as
+           ;; far as they'll go.
+
+           ;; Try to get as much of the comments onscreen as possible.
+           (if (and arg (< ht comment-height))
+               ;; Can't get defun line onscreen; go there and try again.
+               (progn (forward-line (- defun-height))
+                      (beginning-of-line)
+                      (reposition-window))
+             (recenter (min ht comment-height)))
+           ;;(repos-debug-macro "4")
+           ))))
+
+;;; Auxiliary functions
+
+;; Return number of screen lines between START and END.
+(defun repos-count-screen-lines (start end)
+  (save-excursion
+    (save-restriction
+      (narrow-to-region start end)
+      (goto-char (point-min))
+      (vertical-motion (- (point-max) (point-min))))))
+
+;; Return number of screen lines between START and END; returns a negative
+;; number if END precedes START.
+(defun repos-count-screen-lines-signed (start end)
+  (let ((lines (repos-count-screen-lines start end)))
+    (if (< start end)
+        lines
+      (- lines))))
+
+; (defmacro repos-debug-macro (case-no)
+;   (` (message
+;       (concat "Case " (, case-no) ": %s %s %s %s %s")
+;       ht line comment-height defun-height defun-depth)))
+