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1 ;;; reposition.el --- center a Lisp function or comment on the screen
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2
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3 ;; Copyright (C) 1991, 1994 Free Software Foundation, Inc.
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4
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5 ;; Author: Michael D. Ernst <mernst@theory.lcs.mit.edu>
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6 ;; Created: Jan 1991
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7 ;; Maintainer: FSF
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8
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9 ;; This file is part of XEmacs.
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10
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11 ;; XEmacs is free software; you can redistribute it and/or modify it
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12 ;; under the terms of the GNU General Public License as published by
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13 ;; the Free Software Foundation; either version 2, or (at your option)
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14 ;; any later version.
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15
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16 ;; XEmacs is distributed in the hope that it will be useful, but
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17 ;; WITHOUT ANY WARRANTY; without even the implied warranty of
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18 ;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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19 ;; General Public License for more details.
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20
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21 ;; You should have received a copy of the GNU General Public License
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22 ;; along with XEmacs; see the file COPYING. If not, write to the Free
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23 ;; Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.
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24
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25 ;;; Synched up with: FSF 19.30.
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26
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27 ;;; Commentary:
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28
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29 ;;; Reposition-window makes an entire function definition or comment visible,
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30 ;;; or, if it is already visible, places it at the top of the window;
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31 ;;; additional invocations toggle the visibility of comments preceding the
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32 ;;; code. For the gory details, see the documentation for reposition-window;
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33 ;;; rather than reading that, you may just want to play with it.
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34
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35 ;;; This tries pretty hard to do the recentering correctly; the precise
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36 ;;; action depends on what the buffer looks like. If you find a situation
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37 ;;; where it doesn't behave well, let me know. This function is modeled
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38 ;;; after one of the same name in ZMACS, but the code is all-new and the
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39 ;;; behavior in some situations differs.
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40
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41 ;;; Code:
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42
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43 ;;;###autoload
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44 (defun reposition-window (&optional arg)
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45 "Make the current definition and/or comment visible.
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46 Further invocations move it to the top of the window or toggle the
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47 visibility of comments that precede it.
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48 Point is left unchanged unless prefix ARG is supplied.
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49 If the definition is fully onscreen, it is moved to the top of the
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50 window. If it is partly offscreen, the window is scrolled to get the
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51 definition (or as much as will fit) onscreen, unless point is in a comment
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52 which is also partly offscreen, in which case the scrolling attempts to get
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53 as much of the comment onscreen as possible.
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54 Initially `reposition-window' attempts to make both the definition and
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55 preceding comments visible. Further invocations toggle the visibility of
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56 the comment lines.
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57 If ARG is non-nil, point may move in order to make the whole defun
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58 visible (if only part could otherwise be made so), to make the defun line
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59 visible (if point is in code and it could not be made so, or if only
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60 comments, including the first comment line, are visible), or to make the
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61 first comment line visible (if point is in a comment)."
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62 (interactive "P")
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63 (let* (;; (here (save-excursion (beginning-of-line) (point)))
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64 (here (point))
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65 ;; change this name once I've gotten rid of references to ht.
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66 ;; this is actually the number of the last screen line
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67 (ht (- (window-height (selected-window)) 2))
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68 (line (repos-count-screen-lines (window-start) (point)))
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69 (comment-height
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70 ;; The call to max deals with the case of cursor between defuns.
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71 (max 0
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72 (repos-count-screen-lines-signed
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73 ;; the beginning of the preceding comment
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74 (save-excursion
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75 (if (not (eobp)) (forward-char 1))
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76 (end-of-defun -1)
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77 ;; Skip whitespace, newlines, and form feeds.
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78 (if (re-search-forward "[^ \t\n\f]" nil t)
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79 (backward-char 1))
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80 (point))
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81 here)))
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82 (defun-height
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83 (repos-count-screen-lines-signed
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84 (save-excursion
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85 (end-of-defun 1) ; so comments associate with following defuns
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86 (beginning-of-defun 1)
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87 (point))
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88 here))
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89 ;; This must be positive, so don't use the signed version.
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90 (defun-depth (repos-count-screen-lines here
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91 (save-excursion
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92 (end-of-defun 1)
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93 (point))))
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94 (defun-line-onscreen-p
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95 (and (<= defun-height line)
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96 (<= (- line defun-height) ht))))
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97 (cond ((or (= comment-height line)
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98 (and (= line ht)
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99 (> comment-height line)
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100 ;; if defun line offscreen, we should be in case 4
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101 defun-line-onscreen-p))
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102 ;; Either first comment line is at top of screen or (point at
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103 ;; bottom of screen, defun line onscreen, and first comment line
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104 ;; off top of screen). That is, it looks like we just did
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105 ;; recenter-definition, trying to fit as much of the comment
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106 ;; onscreen as possible. Put defun line at top of screen; that
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107 ;; is, show as much code, and as few comments, as possible.
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108
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109 (if (and arg (> defun-depth (1+ ht)))
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110 ;; Can't fit whole defun onscreen without moving point.
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111 (progn (end-of-defun) (beginning-of-defun) (recenter 0))
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112 (recenter (max defun-height 0)))
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113 ;;(repos-debug-macro "1")
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114 )
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115
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116 ((or (= defun-height line)
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117 (= line 0)
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118 (and (< line comment-height)
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119 (< defun-height 0)))
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120 ;; Defun line or cursor at top of screen, OR cursor in comment
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121 ;; whose first line is offscreen.
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122 ;; Avoid moving definition up even if defun runs offscreen;
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123 ;; we care more about getting the comment onscreen.
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124
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125 (cond ((= line ht)
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126 ;; cursor on last screen line (and so in a comment)
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127 (if arg (progn (end-of-defun) (beginning-of-defun)))
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128 (recenter 0)
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129 ;;(repos-debug-macro "2a")
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130 )
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131
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132 ;; This condition, copied from case 4, may not be quite right
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133
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134 ((and arg (< ht comment-height))
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135 ;; Can't get first comment line onscreen.
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136 ;; Go there and try again.
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137 (forward-line (- comment-height))
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138 (beginning-of-line)
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139 ;; was (reposition-window)
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140 (recenter 0)
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141 ;;(repos-debug-macro "2b")
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142 )
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143 (t
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144 (recenter (min ht comment-height))
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145 ;;(repos-debug-macro "2c")
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146 ))
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147 ;; (recenter (min ht comment-height))
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148 )
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149
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150 ((and (> (+ line defun-depth -1) ht)
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151 defun-line-onscreen-p)
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152 ;; Defun runs off the bottom of the screen and the defun line
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153 ;; is onscreen.
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154 ;; Move the defun up.
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155 (recenter (max 0 (1+ (- ht defun-depth)) defun-height))
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156 ;;(repos-debug-macro "3")
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157 )
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158
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159 (t
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160 ;; If on the bottom line and comment start is offscreen
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161 ;; then just move all comments offscreen, or at least as
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162 ;; far as they'll go.
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163
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164 ;; Try to get as much of the comments onscreen as possible.
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165 (if (and arg (< ht comment-height))
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166 ;; Can't get defun line onscreen; go there and try again.
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167 (progn (forward-line (- defun-height))
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168 (beginning-of-line)
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169 (reposition-window))
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170 (recenter (min ht comment-height)))
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171 ;;(repos-debug-macro "4")
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172 ))))
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173
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174 ;;; This key should be bound to switch-to-other-buffer by default so
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175 ;;; don't ###autoload it. -jwz
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176 (define-key esc-map "\C-l" 'reposition-window)
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177
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178 ;;; Auxiliary functions
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179
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180 ;; Return number of screen lines between START and END.
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181 (defun repos-count-screen-lines (start end)
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182 (save-excursion
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183 (save-restriction
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184 (narrow-to-region start end)
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185 (goto-char (point-min))
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186 (vertical-motion (- (point-max) (point-min))))))
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187
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188 ;; Return number of screen lines between START and END; returns a negative
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189 ;; number if END precedes START.
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190 (defun repos-count-screen-lines-signed (start end)
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191 (let ((lines (repos-count-screen-lines start end)))
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192 (if (< start end)
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193 lines
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194 (- lines))))
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195
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196 ; (defmacro repos-debug-macro (case-no)
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197 ; (` (message
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198 ; (concat "Case " (, case-no) ": %s %s %s %s %s")
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199 ; ht line comment-height defun-height defun-depth)))
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200
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201 ;;; reposition.el ends here
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