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30 /****************************************************************************
31  *  Author: Zeyd M. Ben-Halim <zmbenhal@netcom.com> 1992,1995               *
32  *     and: Eric S. Raymond <esr@snark.thyrsus.com>                         *
33  *     and: Thomas E. Dickey                        1996-on                 *
34  *     and: Alexander V Lukyanov                    1997-1998               *
35  ****************************************************************************/
36 
37 /******************************************************************************
38 
39 NAME
40    hardscroll.c -- hardware-scrolling optimization for ncurses
41 
42 SYNOPSIS
43    void _nc_scroll_optimize(void)
44 
45 DESCRIPTION
46 			OVERVIEW
47 
48 This algorithm for computes optimum hardware scrolling to transform an
49 old screen (curscr) into a new screen (newscr) via vertical line moves.
50 
51 Because the screen has a `grain' (there are insert/delete/scroll line
52 operations but no insert/delete/scroll column operations), it is efficient
53 break the update algorithm into two pieces: a first stage that does only line
54 moves, optimizing the end product of user-invoked insertions, deletions, and
55 scrolls; and a second phase (corresponding to the present doupdate code in
56 ncurses) that does only line transformations.
57 
58 The common case we want hardware scrolling for is to handle line insertions
59 and deletions in screen-oriented text-editors.  This two-stage approach will
60 accomplish that at a low computation and code-size cost.
61 
62 			LINE-MOVE COMPUTATION
63 
64 Now, to a discussion of the line-move computation.
65 
66 For expository purposes, consider the screen lines to be represented by
67 integers 0..23 (with the understanding that the value of 23 may vary).
68 Let a new line introduced by insertion, scrolling, or at the bottom of
69 the screen following a line delete be given the index -1.
70 
71 Assume that the real screen starts with lines 0..23.  Now, we have
72 the following possible line-oriented operations on the screen:
73 
74 Insertion: inserts a line at a given screen row, forcing all lines below
75 to scroll forward.  The last screen line is lost.  For example, an insertion
76 at line 5 would produce: 0..4 -1 5..23.
77 
78 Deletion: deletes a line at a given screen row, forcing all lines below
79 to scroll forward.  The last screen line is made new.  For example, a deletion
80 at line 7 would produce: 0..6 8..23 -1.
81 
82 Scroll up: move a range of lines up 1.  The bottom line of the range
83 becomes new.  For example, scrolling up the region from 9 to 14 will
84 produce 0..8 10..14 -1 15..23.
85 
86 Scroll down: move a range of lines down 1.  The top line of the range
87 becomes new.  For example, scrolling down the region from 12 to 16 will produce
88 0..11 -1 12..15 17..23.
89 
90 Now, an obvious property of all these operations is that they preserve the
91 order of old lines, though not their position in the sequence.
92 
93 The key trick of this algorithm is that the original line indices described
94 above are actually maintained as _line[].oldindex fields in the window
95 structure, and stick to each line through scroll and insert/delete operations.
96 
97 Thus, it is possible at update time to look at the oldnum fields and compute
98 an optimal set of il/dl/scroll operations that will take the real screen
99 lines to the virtual screen lines.  Once these vertical moves have been done,
100 we can hand off to the second stage of the update algorithm, which does line
101 transformations.
102 
103 Note that the move computation does not need to have the full generality
104 of a diff algorithm (which it superficially resembles) because lines cannot
105 be moved out of order.
106 
107 			THE ALGORITHM
108 
109 The scrolling is done in two passes. The first pass is from top to bottom
110 scroling hunks UP. The second one is from bottom to top scrolling hunks DOWN.
111 Obviously enough, no lines to be scrolled will be destroyed. (lav)
112 
113 HOW TO TEST THIS:
114 
115 Use the following production:
116 
117 hardscroll: hardscroll.c
118 	$(CC) -g -DSCROLLDEBUG hardscroll.c -o hardscroll
119 
120 Then just type scramble vectors and watch.  The following test loads are
121 a representative sample of cases:
122 
123 -----------------------------  CUT HERE ------------------------------------
124 # No lines moved
125  0  1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
126 #
127 # A scroll up
128  1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 -1
129 #
130 # A scroll down
131 -1  0  1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16 17 18 19 20 21 22
132 #
133 # An insertion (after line 12)
134  0  1  2  3  4  5  6  7  8  9 10 11 12 -1 13 14 15 16 17 18 19 20 21 22
135 #
136 # A simple deletion (line 10)
137  0  1  2  3  4  5  6  7  8  9  11 12 13 14 15 16 17 18 19 20 21 22 23 -1
138 #
139 # A more complex case
140 -1 -1 -1 -1 -1  3  4  5  6  7  -1 -1  8  9 10 11 12 13 14 15 16 17 -1 -1
141 -----------------------------  CUT HERE ------------------------------------
142 
143 AUTHOR
144     Eric S. Raymond <esr@snark.thyrsus.com>, November 1994
145     New algorithm by Alexander V. Lukyanov <lav@yars.free.net>, Aug 1997
146 
147 *****************************************************************************/
148 
149 #include <curses.priv.h>
150 
151 MODULE_ID("$Id: hardscroll.c,v 1.54 2020/02/02 23:34:34 tom Exp $")
152 
153 #if defined(SCROLLDEBUG) || defined(HASHDEBUG)
154 
155 # undef screen_lines
156 # define screen_lines(sp) MAXLINES
157 NCURSES_EXPORT_VAR (int)
158   oldnums[MAXLINES];
159 # define OLDNUM(sp,n)	oldnums[n]
160 # define _tracef	printf
161 # undef TR
162 # define TR(n, a)	if (_nc_tracing & (n)) { _tracef a ; putchar('\n'); }
163 
164 extern				NCURSES_EXPORT_VAR(unsigned) _nc_tracing;
165 
166 #else /* no debug */
167 
168 /* OLDNUM(n) indicates which line will be shifted to the position n.
169    if OLDNUM(n) == _NEWINDEX, then the line n in new, not shifted from
170    somewhere. */
171 NCURSES_EXPORT_VAR (int *)
172   _nc_oldnums = 0;		/* obsolete: keep for ABI compat */
173 
174 # if USE_HASHMAP
175 #  define oldnums(sp)   (sp)->_oldnum_list
176 #  define OLDNUM(sp,n)	oldnums(sp)[n]
177 # else /* !USE_HASHMAP */
178 #  define OLDNUM(sp,n)	NewScreen(sp)->_line[n].oldindex
179 # endif	/* !USE_HASHMAP */
180 
181 #define OLDNUM_SIZE(sp) (sp)->_oldnum_size
182 
183 #endif /* defined(SCROLLDEBUG) || defined(HASHDEBUG) */
184 
185 NCURSES_EXPORT(void)
NCURSES_SP_NAME(_nc_scroll_optimize)186 NCURSES_SP_NAME(_nc_scroll_optimize) (NCURSES_SP_DCL0)
187 /* scroll optimization to transform curscr to newscr */
188 {
189     int i;
190     int start, end, shift;
191 
192     TR(TRACE_ICALLS, (T_CALLED("_nc_scroll_optimize(%p)"), (void *) SP_PARM));
193 
194 #if !defined(SCROLLDEBUG) && !defined(HASHDEBUG)
195 #if USE_HASHMAP
196     /* get enough storage */
197     assert(OLDNUM_SIZE(SP_PARM) >= 0);
198     assert(screen_lines(SP_PARM) > 0);
199     if ((oldnums(SP_PARM) == 0)
200 	|| (OLDNUM_SIZE(SP_PARM) < screen_lines(SP_PARM))) {
201 	int need_lines = ((OLDNUM_SIZE(SP_PARM) < screen_lines(SP_PARM))
202 			  ? screen_lines(SP_PARM)
203 			  : OLDNUM_SIZE(SP_PARM));
204 	int *new_oldnums = typeRealloc(int,
205 				       (size_t) need_lines,
206 				       oldnums(SP_PARM));
207 	if (!new_oldnums)
208 	    return;
209 	oldnums(SP_PARM) = new_oldnums;
210 	OLDNUM_SIZE(SP_PARM) = need_lines;
211     }
212     /* calculate the indices */
213     NCURSES_SP_NAME(_nc_hash_map) (NCURSES_SP_ARG);
214 #endif
215 #endif /* !defined(SCROLLDEBUG) && !defined(HASHDEBUG) */
216 
217 #ifdef TRACE
218     if (USE_TRACEF(TRACE_UPDATE | TRACE_MOVE)) {
219 	NCURSES_SP_NAME(_nc_linedump) (NCURSES_SP_ARG);
220 	_nc_unlock_global(tracef);
221     }
222 #endif /* TRACE */
223 
224     /* pass 1 - from top to bottom scrolling up */
225     for (i = 0; i < screen_lines(SP_PARM);) {
226 	while (i < screen_lines(SP_PARM)
227 	       && (OLDNUM(SP_PARM, i) == _NEWINDEX || OLDNUM(SP_PARM, i) <= i))
228 	    i++;
229 	if (i >= screen_lines(SP_PARM))
230 	    break;
231 
232 	shift = OLDNUM(SP_PARM, i) - i;		/* shift > 0 */
233 	start = i;
234 
235 	i++;
236 	while (i < screen_lines(SP_PARM)
237 	       && OLDNUM(SP_PARM, i) != _NEWINDEX
238 	       && OLDNUM(SP_PARM, i) - i == shift)
239 	    i++;
240 	end = i - 1 + shift;
241 
242 	TR(TRACE_UPDATE | TRACE_MOVE, ("scroll [%d, %d] by %d", start, end, shift));
243 #if !defined(SCROLLDEBUG) && !defined(HASHDEBUG)
244 	if (NCURSES_SP_NAME(_nc_scrolln) (NCURSES_SP_ARGx
245 					  shift,
246 					  start,
247 					  end,
248 					  screen_lines(SP_PARM) - 1) == ERR) {
249 	    TR(TRACE_UPDATE | TRACE_MOVE, ("unable to scroll"));
250 	    continue;
251 	}
252 #endif /* !defined(SCROLLDEBUG) && !defined(HASHDEBUG) */
253     }
254 
255     /* pass 2 - from bottom to top scrolling down */
256     for (i = screen_lines(SP_PARM) - 1; i >= 0;) {
257 	while (i >= 0
258 	       && (OLDNUM(SP_PARM, i) == _NEWINDEX
259 		   || OLDNUM(SP_PARM, i) >= i)) {
260 	    i--;
261 	}
262 	if (i < 0)
263 	    break;
264 
265 	shift = OLDNUM(SP_PARM, i) - i;		/* shift < 0 */
266 	end = i;
267 
268 	i--;
269 	while (i >= 0
270 	       && OLDNUM(SP_PARM, i) != _NEWINDEX
271 	       && OLDNUM(SP_PARM, i) - i == shift) {
272 	    i--;
273 	}
274 	start = i + 1 - (-shift);
275 
276 	TR(TRACE_UPDATE | TRACE_MOVE, ("scroll [%d, %d] by %d", start, end, shift));
277 #if !defined(SCROLLDEBUG) && !defined(HASHDEBUG)
278 	if (NCURSES_SP_NAME(_nc_scrolln) (NCURSES_SP_ARGx
279 					  shift,
280 					  start,
281 					  end,
282 					  screen_lines(SP_PARM) - 1) == ERR) {
283 	    TR(TRACE_UPDATE | TRACE_MOVE, ("unable to scroll"));
284 	    continue;
285 	}
286 #endif /* !defined(SCROLLDEBUG) && !defined(HASHDEBUG) */
287     }
288     TR(TRACE_ICALLS, (T_RETURN("")));
289 }
290 
291 #if NCURSES_SP_FUNCS
292 NCURSES_EXPORT(void)
_nc_scroll_optimize(void)293 _nc_scroll_optimize(void)
294 {
295     NCURSES_SP_NAME(_nc_scroll_optimize) (CURRENT_SCREEN);
296 }
297 #endif
298 
299 #if defined(TRACE) || defined(SCROLLDEBUG) || defined(HASHDEBUG)
300 NCURSES_EXPORT(void)
NCURSES_SP_NAME(_nc_linedump)301 NCURSES_SP_NAME(_nc_linedump) (NCURSES_SP_DCL0)
302 /* dump the state of the real and virtual oldnum fields */
303 {
304     char *buf = 0;
305     size_t want = ((size_t) screen_lines(SP_PARM) + 1) * 4;
306     (void) SP_PARM;
307 
308     if ((buf = typeMalloc(char, want)) != 0) {
309 	int n;
310 
311 	*buf = '\0';
312 	for (n = 0; n < screen_lines(SP_PARM); n++)
313 	    _nc_SPRINTF(buf + strlen(buf),
314 			_nc_SLIMIT(want - strlen(buf))
315 			" %02d", OLDNUM(SP_PARM, n));
316 	TR(TRACE_UPDATE | TRACE_MOVE, ("virt %s", buf));
317 	free(buf);
318     }
319 }
320 
321 #if NCURSES_SP_FUNCS
322 NCURSES_EXPORT(void)
_nc_linedump(void)323 _nc_linedump(void)
324 {
325     NCURSES_SP_NAME(_nc_linedump) (CURRENT_SCREEN);
326 }
327 #endif
328 
329 #endif /* defined(TRACE) || defined(SCROLLDEBUG) */
330 
331 #ifdef SCROLLDEBUG
332 
333 int
main(int argc GCC_UNUSED,char * argv[]GCC_UNUSED)334 main(int argc GCC_UNUSED, char *argv[]GCC_UNUSED)
335 {
336     char line[BUFSIZ], *st;
337 
338 #ifdef TRACE
339     _nc_tracing = TRACE_MOVE;
340 #endif
341     for (;;) {
342 	int n;
343 
344 	for (n = 0; n < screen_lines(sp); n++)
345 	    oldnums[n] = _NEWINDEX;
346 
347 	/* grab the test vector */
348 	if (fgets(line, sizeof(line), stdin) == (char *) NULL)
349 	    exit(EXIT_SUCCESS);
350 
351 	/* parse it */
352 	n = 0;
353 	if (line[0] == '#') {
354 	    (void) fputs(line, stderr);
355 	    continue;
356 	}
357 	st = strtok(line, " ");
358 	do {
359 	    oldnums[n++] = atoi(st);
360 	} while
361 	    ((st = strtok((char *) NULL, " ")) != 0);
362 
363 	/* display it */
364 	(void) fputs("Initial input:\n", stderr);
365 	_nc_linedump();
366 
367 	_nc_scroll_optimize();
368     }
369 }
370 
371 #endif /* SCROLLDEBUG */
372 
373 /* hardscroll.c ends here */
374