1 /*
2 * Copyright (C) 1984-2025 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 LONGTIME (2) /* In seconds */
59
60 static struct linenum_info anchor; /* Anchor of the list */
61 static struct linenum_info *freelist; /* Anchor of the unused entries */
62 static struct linenum_info pool[LINENUM_POOL]; /* The pool itself */
63 static struct linenum_info *spare; /* We always keep one spare entry */
64 public lbool scanning_eof = FALSE;
65
66 extern int linenums;
67 extern int sigs;
68 extern int sc_height;
69 extern int header_lines;
70 extern int nonum_headers;
71 extern POSITION header_start_pos;
72
73 /*
74 * Initialize the line number structures.
75 */
clr_linenum(void)76 public void clr_linenum(void)
77 {
78 struct linenum_info *p;
79
80 /*
81 * Put all the entries on the free list.
82 * Leave one for the "spare".
83 */
84 for (p = pool; p < &pool[LINENUM_POOL-2]; p++)
85 p->next = p+1;
86 pool[LINENUM_POOL-2].next = NULL;
87 freelist = pool;
88
89 spare = &pool[LINENUM_POOL-1];
90
91 /*
92 * Initialize the anchor.
93 */
94 anchor.next = anchor.prev = &anchor;
95 anchor.gap = 0;
96 anchor.pos = (POSITION)0;
97 anchor.line = 1;
98 }
99
100 /*
101 * Calculate the gap for an entry.
102 */
calcgap(struct linenum_info * p)103 static void calcgap(struct linenum_info *p)
104 {
105 /*
106 * Don't bother to compute a gap for the anchor.
107 * Also don't compute a gap for the last one in the list.
108 * The gap for that last one should be considered infinite,
109 * but we never look at it anyway.
110 */
111 if (p == &anchor || p->next == &anchor)
112 return;
113 p->gap = p->next->pos - p->prev->pos;
114 }
115
116 /*
117 * Add a new line number to the cache.
118 * The specified position (pos) should be the file position of the
119 * FIRST character in the specified line.
120 */
add_lnum(LINENUM linenum,POSITION pos)121 public void add_lnum(LINENUM linenum, POSITION pos)
122 {
123 struct linenum_info *p;
124 struct linenum_info *new;
125 struct linenum_info *nextp;
126 struct linenum_info *prevp;
127 POSITION mingap;
128
129 /*
130 * Find the proper place in the list for the new one.
131 * The entries are sorted by position.
132 */
133 for (p = anchor.next; p != &anchor && p->pos < pos; p = p->next)
134 if (p->line == linenum)
135 /* We already have this one. */
136 return;
137 nextp = p;
138 prevp = p->prev;
139
140 if (freelist != NULL)
141 {
142 /*
143 * We still have free (unused) entries.
144 * Use one of them.
145 */
146 new = freelist;
147 freelist = freelist->next;
148 } else
149 {
150 /*
151 * No free entries.
152 * Use the "spare" entry.
153 */
154 new = spare;
155 spare = NULL;
156 }
157
158 /*
159 * Fill in the fields of the new entry,
160 * and insert it into the proper place in the list.
161 */
162 new->next = nextp;
163 new->prev = prevp;
164 new->pos = pos;
165 new->line = linenum;
166
167 nextp->prev = new;
168 prevp->next = new;
169
170 /*
171 * Recalculate gaps for the new entry and the neighboring entries.
172 */
173 calcgap(new);
174 calcgap(nextp);
175 calcgap(prevp);
176
177 if (spare == NULL)
178 {
179 /*
180 * We have used the spare entry.
181 * Scan the list to find the one with the smallest
182 * gap, take it out and make it the spare.
183 * We should never remove the last one, so stop when
184 * we get to p->next == &anchor. This also avoids
185 * looking at the gap of the last one, which is
186 * not computed by calcgap.
187 */
188 mingap = anchor.next->gap;
189 for (p = anchor.next; p->next != &anchor; p = p->next)
190 {
191 if (p->gap <= mingap)
192 {
193 spare = p;
194 mingap = p->gap;
195 }
196 }
197 spare->next->prev = spare->prev;
198 spare->prev->next = spare->next;
199 }
200 }
201
202 /*
203 * If we get stuck in a long loop trying to figure out the
204 * line number, print a message to tell the user what we're doing.
205 */
longloopmessage(void)206 static void longloopmessage(void)
207 {
208 ierror("Calculating line numbers", NULL_PARG);
209 }
210
211 struct delayed_msg
212 {
213 void (*message)(void);
214 int loopcount;
215 #if HAVE_TIME
216 time_type startime;
217 #endif
218 };
219
start_delayed_msg(struct delayed_msg * dmsg,void (* message)(void))220 static void start_delayed_msg(struct delayed_msg *dmsg, void (*message)(void))
221 {
222 dmsg->loopcount = 0;
223 dmsg->message = message;
224 #if HAVE_TIME
225 dmsg->startime = get_time();
226 #endif
227 }
228
delayed_msg(struct delayed_msg * dmsg)229 static void delayed_msg(struct delayed_msg *dmsg)
230 {
231 #if HAVE_TIME
232 if (dmsg->loopcount >= 0 && ++(dmsg->loopcount) > 100)
233 {
234 dmsg->loopcount = 0;
235 if (get_time() >= dmsg->startime + LONGTIME)
236 {
237 dmsg->message();
238 dmsg->loopcount = -1;
239 }
240 }
241 #else
242 if (dmsg->loopcount >= 0 && ++(dmsg->loopcount) > LONGLOOP)
243 {
244 dmsg->message();
245 dmsg->loopcount = -1;
246 }
247 #endif
248 }
249
250 /*
251 * Turn off line numbers because the user has interrupted
252 * a lengthy line number calculation.
253 */
abort_delayed_msg(struct delayed_msg * dmsg)254 static void abort_delayed_msg(struct delayed_msg *dmsg)
255 {
256 if (dmsg->loopcount >= 0)
257 return;
258 if (linenums == OPT_ONPLUS)
259 /*
260 * We were displaying line numbers, so need to repaint.
261 */
262 screen_trashed();
263 linenums = 0;
264 error("Line numbers turned off", NULL_PARG);
265 }
266
267 /*
268 * Find the line number associated with a given position.
269 * Return 0 if we can't figure it out.
270 */
find_linenum(POSITION pos)271 public LINENUM find_linenum(POSITION pos)
272 {
273 struct linenum_info *p;
274 LINENUM linenum;
275 POSITION cpos;
276 struct delayed_msg dmsg;
277
278 if (!linenums)
279 /*
280 * We're not using line numbers.
281 */
282 return (0);
283 if (pos == NULL_POSITION)
284 /*
285 * Caller doesn't know what he's talking about.
286 */
287 return (0);
288 if (pos <= ch_zero())
289 /*
290 * Beginning of file is always line number 1.
291 */
292 return (1);
293
294 /*
295 * Find the entry nearest to the position we want.
296 */
297 for (p = anchor.next; p != &anchor && p->pos < pos; p = p->next)
298 continue;
299 if (p->pos == pos)
300 /* Found it exactly. */
301 return (p->line);
302
303 /*
304 * This is the (possibly) time-consuming part.
305 * We start at the line we just found and start
306 * reading the file forward or backward till we
307 * get to the place we want.
308 *
309 * First decide whether we should go forward from the
310 * previous one or backwards from the next one.
311 * The decision is based on which way involves
312 * traversing fewer bytes in the file.
313 */
314 start_delayed_msg(&dmsg, longloopmessage);
315 if (p == &anchor || pos - p->prev->pos < p->pos - pos)
316 {
317 /*
318 * Go forward.
319 */
320 p = p->prev;
321 if (ch_seek(p->pos))
322 return (0);
323 for (linenum = p->line, cpos = p->pos; cpos < pos; linenum++)
324 {
325 /*
326 * Allow a signal to abort this loop.
327 */
328 cpos = forw_raw_line(cpos, NULL, NULL);
329 if (ABORT_SIGS()) {
330 abort_delayed_msg(&dmsg);
331 return (0);
332 }
333 if (cpos == NULL_POSITION)
334 return (0);
335 delayed_msg(&dmsg);
336 }
337 /*
338 * We might as well cache it.
339 */
340 add_lnum(linenum, cpos);
341 /*
342 * If the given position is not at the start of a line,
343 * make sure we return the correct line number.
344 */
345 if (cpos > pos)
346 linenum--;
347 } else
348 {
349 /*
350 * Go backward.
351 */
352 if (ch_seek(p->pos))
353 return (0);
354 for (linenum = p->line, cpos = p->pos; cpos > pos; linenum--)
355 {
356 /*
357 * Allow a signal to abort this loop.
358 */
359 cpos = back_raw_line(cpos, NULL, NULL);
360 if (ABORT_SIGS()) {
361 abort_delayed_msg(&dmsg);
362 return (0);
363 }
364 if (cpos == NULL_POSITION)
365 return (0);
366 delayed_msg(&dmsg);
367 }
368 /*
369 * We might as well cache it.
370 */
371 add_lnum(linenum, cpos);
372 }
373 return (linenum);
374 }
375
376 /*
377 * Find the position of a given line number.
378 * Return NULL_POSITION if we can't figure it out.
379 */
find_pos(LINENUM linenum)380 public POSITION find_pos(LINENUM linenum)
381 {
382 struct linenum_info *p;
383 POSITION cpos;
384 LINENUM clinenum;
385
386 if (linenum <= 1)
387 /*
388 * Line number 1 is beginning of file.
389 */
390 return (ch_zero());
391
392 /*
393 * Find the entry nearest to the line number we want.
394 */
395 for (p = anchor.next; p != &anchor && p->line < linenum; p = p->next)
396 continue;
397 if (p->line == linenum)
398 /* Found it exactly. */
399 return (p->pos);
400
401 if (p == &anchor || linenum - p->prev->line < p->line - linenum)
402 {
403 /*
404 * Go forward.
405 */
406 p = p->prev;
407 if (ch_seek(p->pos))
408 return (NULL_POSITION);
409 for (clinenum = p->line, cpos = p->pos; clinenum < linenum; clinenum++)
410 {
411 /*
412 * Allow a signal to abort this loop.
413 */
414 cpos = forw_raw_line(cpos, NULL, NULL);
415 if (ABORT_SIGS())
416 return (NULL_POSITION);
417 if (cpos == NULL_POSITION)
418 return (NULL_POSITION);
419 }
420 } else
421 {
422 /*
423 * Go backward.
424 */
425 if (ch_seek(p->pos))
426 return (NULL_POSITION);
427 for (clinenum = p->line, cpos = p->pos; clinenum > linenum; clinenum--)
428 {
429 /*
430 * Allow a signal to abort this loop.
431 */
432 cpos = back_raw_line(cpos, NULL, NULL);
433 if (ABORT_SIGS())
434 return (NULL_POSITION);
435 if (cpos == NULL_POSITION)
436 return (NULL_POSITION);
437 }
438 }
439 /*
440 * We might as well cache it.
441 */
442 add_lnum(clinenum, cpos);
443 return (cpos);
444 }
445
446 /*
447 * Return the line number of the "current" line.
448 * The argument "where" tells which line is to be considered
449 * the "current" line (e.g. TOP, BOTTOM, MIDDLE, etc).
450 */
currline(int where)451 public LINENUM currline(int where)
452 {
453 POSITION pos;
454 POSITION len;
455 LINENUM linenum;
456
457 pos = position(where);
458 len = ch_length();
459 while (pos == NULL_POSITION && where >= 0 && where < sc_height)
460 pos = position(++where);
461 if (pos == NULL_POSITION)
462 pos = len;
463 linenum = find_linenum(pos);
464 if (pos == len)
465 linenum--;
466 return (linenum);
467 }
468
detlenmessage(void)469 static void detlenmessage(void)
470 {
471 ierror("Determining length of file", NULL_PARG);
472 }
473
474 /*
475 * Scan entire file, counting line numbers.
476 */
scan_eof(void)477 public void scan_eof(void)
478 {
479 POSITION pos = ch_zero();
480 LINENUM linenum = 0;
481 struct delayed_msg dmsg;
482
483 if (ch_seek(0))
484 return;
485 /*
486 * scanning_eof prevents the "Waiting for data" message from
487 * overwriting "Determining length of file".
488 */
489 start_delayed_msg(&dmsg, detlenmessage);
490 scanning_eof = TRUE;
491 while (pos != NULL_POSITION)
492 {
493 /* For efficiency, only add one every 256 line numbers. */
494 if ((linenum++ % 256) == 0)
495 add_lnum(linenum, pos);
496 pos = forw_raw_line(pos, NULL, NULL);
497 if (ABORT_SIGS())
498 {
499 abort_delayed_msg(&dmsg);
500 break;
501 }
502 delayed_msg(&dmsg);
503 }
504 scanning_eof = FALSE;
505 }
506
507 /*
508 * Return a line number adjusted for display
509 * (handles the --no-number-headers option).
510 */
vlinenum(LINENUM linenum)511 public LINENUM vlinenum(LINENUM linenum)
512 {
513 if (nonum_headers && header_lines > 0)
514 {
515 LINENUM header_start_line = find_linenum(header_start_pos);
516 if (header_start_line != 0)
517 {
518 LINENUM header_end_line = header_start_line + header_lines; /* first line after header */
519 linenum = (linenum < header_end_line) ? 0 : linenum - header_end_line + 1;
520 }
521 }
522 return linenum;
523 }
524