1 /*
2 * Copyright (C) 1984-2023 Mark Nudelman
3 *
4 * You may distribute under the terms of either the GNU General Public
5 * License or the Less License, as specified in the README file.
6 *
7 * For more information, see the README file.
8 */
9
10
11 /*
12 * Code to handle displaying line numbers.
13 *
14 * Finding the line number of a given file position is rather tricky.
15 * We don't want to just start at the beginning of the file and
16 * count newlines, because that is slow for large files (and also
17 * wouldn't work if we couldn't get to the start of the file; e.g.
18 * if input is a long pipe).
19 *
20 * So we use the function add_lnum to cache line numbers.
21 * We try to be very clever and keep only the more interesting
22 * line numbers when we run out of space in our table. A line
23 * number is more interesting than another when it is far from
24 * other line numbers. For example, we'd rather keep lines
25 * 100,200,300 than 100,101,300. 200 is more interesting than
26 * 101 because 101 can be derived very cheaply from 100, while
27 * 200 is more expensive to derive from 100.
28 *
29 * The function currline() returns the line number of a given
30 * position in the file. As a side effect, it calls add_lnum
31 * to cache the line number. Therefore currline is occasionally
32 * called to make sure we cache line numbers often enough.
33 */
34
35 #include "less.h"
36
37 /*
38 * Structure to keep track of a line number and the associated file position.
39 * A doubly-linked circular list of line numbers is kept ordered by line number.
40 */
41 struct linenum_info
42 {
43 struct linenum_info *next; /* Link to next in the list */
44 struct linenum_info *prev; /* Line to previous in the list */
45 POSITION pos; /* File position */
46 POSITION gap; /* Gap between prev and next */
47 LINENUM line; /* Line number */
48 };
49 /*
50 * "gap" needs some explanation: the gap of any particular line number
51 * is the distance between the previous one and the next one in the list.
52 * ("Distance" means difference in file position.) In other words, the
53 * gap of a line number is the gap which would be introduced if this
54 * line number were deleted. It is used to decide which one to replace
55 * when we have a new one to insert and the table is full.
56 */
57
58 #define NPOOL 200 /* Size of line number pool */
59
60 #define LONGTIME (2) /* In seconds */
61
62 static struct linenum_info anchor; /* Anchor of the list */
63 static struct linenum_info *freelist; /* Anchor of the unused entries */
64 static struct linenum_info pool[NPOOL]; /* The pool itself */
65 static struct linenum_info *spare; /* We always keep one spare entry */
66 public int scanning_eof = FALSE;
67
68 extern int linenums;
69 extern int sigs;
70 extern int sc_height;
71 extern int screen_trashed;
72 extern int header_lines;
73 extern int nonum_headers;
74
75 /*
76 * Initialize the line number structures.
77 */
clr_linenum(void)78 public void clr_linenum(void)
79 {
80 struct linenum_info *p;
81
82 /*
83 * Put all the entries on the free list.
84 * Leave one for the "spare".
85 */
86 for (p = pool; p < &pool[NPOOL-2]; p++)
87 p->next = p+1;
88 pool[NPOOL-2].next = NULL;
89 freelist = pool;
90
91 spare = &pool[NPOOL-1];
92
93 /*
94 * Initialize the anchor.
95 */
96 anchor.next = anchor.prev = &anchor;
97 anchor.gap = 0;
98 anchor.pos = (POSITION)0;
99 anchor.line = 1;
100 }
101
102 /*
103 * Calculate the gap for an entry.
104 */
calcgap(struct linenum_info * p)105 static void calcgap(struct linenum_info *p)
106 {
107 /*
108 * Don't bother to compute a gap for the anchor.
109 * Also don't compute a gap for the last one in the list.
110 * The gap for that last one should be considered infinite,
111 * but we never look at it anyway.
112 */
113 if (p == &anchor || p->next == &anchor)
114 return;
115 p->gap = p->next->pos - p->prev->pos;
116 }
117
118 /*
119 * Add a new line number to the cache.
120 * The specified position (pos) should be the file position of the
121 * FIRST character in the specified line.
122 */
add_lnum(LINENUM linenum,POSITION pos)123 public void add_lnum(LINENUM linenum, POSITION pos)
124 {
125 struct linenum_info *p;
126 struct linenum_info *new;
127 struct linenum_info *nextp;
128 struct linenum_info *prevp;
129 POSITION mingap;
130
131 /*
132 * Find the proper place in the list for the new one.
133 * The entries are sorted by position.
134 */
135 for (p = anchor.next; p != &anchor && p->pos < pos; p = p->next)
136 if (p->line == linenum)
137 /* We already have this one. */
138 return;
139 nextp = p;
140 prevp = p->prev;
141
142 if (freelist != NULL)
143 {
144 /*
145 * We still have free (unused) entries.
146 * Use one of them.
147 */
148 new = freelist;
149 freelist = freelist->next;
150 } else
151 {
152 /*
153 * No free entries.
154 * Use the "spare" entry.
155 */
156 new = spare;
157 spare = NULL;
158 }
159
160 /*
161 * Fill in the fields of the new entry,
162 * and insert it into the proper place in the list.
163 */
164 new->next = nextp;
165 new->prev = prevp;
166 new->pos = pos;
167 new->line = linenum;
168
169 nextp->prev = new;
170 prevp->next = new;
171
172 /*
173 * Recalculate gaps for the new entry and the neighboring entries.
174 */
175 calcgap(new);
176 calcgap(nextp);
177 calcgap(prevp);
178
179 if (spare == NULL)
180 {
181 /*
182 * We have used the spare entry.
183 * Scan the list to find the one with the smallest
184 * gap, take it out and make it the spare.
185 * We should never remove the last one, so stop when
186 * we get to p->next == &anchor. This also avoids
187 * looking at the gap of the last one, which is
188 * not computed by calcgap.
189 */
190 mingap = anchor.next->gap;
191 for (p = anchor.next; p->next != &anchor; p = p->next)
192 {
193 if (p->gap <= mingap)
194 {
195 spare = p;
196 mingap = p->gap;
197 }
198 }
199 spare->next->prev = spare->prev;
200 spare->prev->next = spare->next;
201 }
202 }
203
204 /*
205 * If we get stuck in a long loop trying to figure out the
206 * line number, print a message to tell the user what we're doing.
207 */
longloopmessage(void)208 static void longloopmessage(void)
209 {
210 ierror("Calculating line numbers", NULL_PARG);
211 }
212
213 static int loopcount;
214 #if HAVE_TIME
215 static time_type startime;
216 #endif
217
longish(void)218 static void longish(void)
219 {
220 #if HAVE_TIME
221 if (loopcount >= 0 && ++loopcount > 100)
222 {
223 loopcount = 0;
224 if (get_time() >= startime + LONGTIME)
225 {
226 longloopmessage();
227 loopcount = -1;
228 }
229 }
230 #else
231 if (loopcount >= 0 && ++loopcount > LONGLOOP)
232 {
233 longloopmessage();
234 loopcount = -1;
235 }
236 #endif
237 }
238
239 /*
240 * Turn off line numbers because the user has interrupted
241 * a lengthy line number calculation.
242 */
abort_long(void)243 static void abort_long(void)
244 {
245 if (loopcount >= 0)
246 return;
247 if (linenums == OPT_ONPLUS)
248 /*
249 * We were displaying line numbers, so need to repaint.
250 */
251 screen_trashed = 1;
252 linenums = 0;
253 error("Line numbers turned off", NULL_PARG);
254 }
255
256 /*
257 * Find the line number associated with a given position.
258 * Return 0 if we can't figure it out.
259 */
find_linenum(POSITION pos)260 public LINENUM find_linenum(POSITION pos)
261 {
262 struct linenum_info *p;
263 LINENUM linenum;
264 POSITION cpos;
265
266 if (!linenums)
267 /*
268 * We're not using line numbers.
269 */
270 return (0);
271 if (pos == NULL_POSITION)
272 /*
273 * Caller doesn't know what he's talking about.
274 */
275 return (0);
276 if (pos <= ch_zero())
277 /*
278 * Beginning of file is always line number 1.
279 */
280 return (1);
281
282 /*
283 * Find the entry nearest to the position we want.
284 */
285 for (p = anchor.next; p != &anchor && p->pos < pos; p = p->next)
286 continue;
287 if (p->pos == pos)
288 /* Found it exactly. */
289 return (p->line);
290
291 /*
292 * This is the (possibly) time-consuming part.
293 * We start at the line we just found and start
294 * reading the file forward or backward till we
295 * get to the place we want.
296 *
297 * First decide whether we should go forward from the
298 * previous one or backwards from the next one.
299 * The decision is based on which way involves
300 * traversing fewer bytes in the file.
301 */
302 #if HAVE_TIME
303 startime = get_time();
304 #endif
305 loopcount = 0;
306 if (p == &anchor || pos - p->prev->pos < p->pos - pos)
307 {
308 /*
309 * Go forward.
310 */
311 p = p->prev;
312 if (ch_seek(p->pos))
313 return (0);
314 for (linenum = p->line, cpos = p->pos; cpos < pos; linenum++)
315 {
316 /*
317 * Allow a signal to abort this loop.
318 */
319 cpos = forw_raw_line(cpos, (char **)NULL, (int *)NULL);
320 if (ABORT_SIGS()) {
321 abort_long();
322 return (0);
323 }
324 if (cpos == NULL_POSITION)
325 return (0);
326 longish();
327 }
328 /*
329 * We might as well cache it.
330 */
331 add_lnum(linenum, cpos);
332 /*
333 * If the given position is not at the start of a line,
334 * make sure we return the correct line number.
335 */
336 if (cpos > pos)
337 linenum--;
338 } else
339 {
340 /*
341 * Go backward.
342 */
343 if (ch_seek(p->pos))
344 return (0);
345 for (linenum = p->line, cpos = p->pos; cpos > pos; linenum--)
346 {
347 /*
348 * Allow a signal to abort this loop.
349 */
350 cpos = back_raw_line(cpos, (char **)NULL, (int *)NULL);
351 if (ABORT_SIGS()) {
352 abort_long();
353 return (0);
354 }
355 if (cpos == NULL_POSITION)
356 return (0);
357 longish();
358 }
359 /*
360 * We might as well cache it.
361 */
362 add_lnum(linenum, cpos);
363 }
364 loopcount = 0;
365 return (linenum);
366 }
367
368 /*
369 * Find the position of a given line number.
370 * Return NULL_POSITION if we can't figure it out.
371 */
find_pos(LINENUM linenum)372 public POSITION find_pos(LINENUM linenum)
373 {
374 struct linenum_info *p;
375 POSITION cpos;
376 LINENUM clinenum;
377
378 if (linenum <= 1)
379 /*
380 * Line number 1 is beginning of file.
381 */
382 return (ch_zero());
383
384 /*
385 * Find the entry nearest to the line number we want.
386 */
387 for (p = anchor.next; p != &anchor && p->line < linenum; p = p->next)
388 continue;
389 if (p->line == linenum)
390 /* Found it exactly. */
391 return (p->pos);
392
393 if (p == &anchor || linenum - p->prev->line < p->line - linenum)
394 {
395 /*
396 * Go forward.
397 */
398 p = p->prev;
399 if (ch_seek(p->pos))
400 return (NULL_POSITION);
401 for (clinenum = p->line, cpos = p->pos; clinenum < linenum; clinenum++)
402 {
403 /*
404 * Allow a signal to abort this loop.
405 */
406 cpos = forw_raw_line(cpos, (char **)NULL, (int *)NULL);
407 if (ABORT_SIGS())
408 return (NULL_POSITION);
409 if (cpos == NULL_POSITION)
410 return (NULL_POSITION);
411 }
412 } else
413 {
414 /*
415 * Go backward.
416 */
417 if (ch_seek(p->pos))
418 return (NULL_POSITION);
419 for (clinenum = p->line, cpos = p->pos; clinenum > linenum; clinenum--)
420 {
421 /*
422 * Allow a signal to abort this loop.
423 */
424 cpos = back_raw_line(cpos, (char **)NULL, (int *)NULL);
425 if (ABORT_SIGS())
426 return (NULL_POSITION);
427 if (cpos == NULL_POSITION)
428 return (NULL_POSITION);
429 }
430 }
431 /*
432 * We might as well cache it.
433 */
434 add_lnum(clinenum, cpos);
435 return (cpos);
436 }
437
438 /*
439 * Return the line number of the "current" line.
440 * The argument "where" tells which line is to be considered
441 * the "current" line (e.g. TOP, BOTTOM, MIDDLE, etc).
442 */
currline(int where)443 public LINENUM currline(int where)
444 {
445 POSITION pos;
446 POSITION len;
447 LINENUM linenum;
448
449 pos = position(where);
450 len = ch_length();
451 while (pos == NULL_POSITION && where >= 0 && where < sc_height)
452 pos = position(++where);
453 if (pos == NULL_POSITION)
454 pos = len;
455 linenum = find_linenum(pos);
456 if (pos == len)
457 linenum--;
458 return (linenum);
459 }
460
461 /*
462 * Scan entire file, counting line numbers.
463 */
scan_eof(void)464 public void scan_eof(void)
465 {
466 POSITION pos = ch_zero();
467 LINENUM linenum = 0;
468
469 if (ch_seek(0))
470 return;
471 ierror("Determining length of file", NULL_PARG);
472 /*
473 * scanning_eof prevents the "Waiting for data" message from
474 * overwriting "Determining length of file".
475 */
476 scanning_eof = TRUE;
477 while (pos != NULL_POSITION)
478 {
479 /* For efficiency, only add one every 256 line numbers. */
480 if ((linenum++ % 256) == 0)
481 add_lnum(linenum, pos);
482 pos = forw_raw_line(pos, (char **)NULL, (int *)NULL);
483 if (ABORT_SIGS())
484 break;
485 }
486 scanning_eof = FALSE;
487 }
488
489 /*
490 * Return a line number adjusted for display
491 * (handles the --no-number-headers option).
492 */
vlinenum(LINENUM linenum)493 public LINENUM vlinenum(LINENUM linenum)
494 {
495 if (nonum_headers)
496 linenum = (linenum < header_lines) ? 0 : linenum - header_lines;
497 return linenum;
498 }
499