1 /*
2 * Copyright (C) 1984-2021 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
67 extern int linenums;
68 extern int sigs;
69 extern int sc_height;
70 extern int screen_trashed;
71
72 /*
73 * Initialize the line number structures.
74 */
75 public void
clr_linenum(VOID_PARAM)76 clr_linenum(VOID_PARAM)
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[NPOOL-2]; p++)
85 p->next = p+1;
86 pool[NPOOL-2].next = NULL;
87 freelist = pool;
88
89 spare = &pool[NPOOL-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 */
103 static void
calcgap(p)104 calcgap(p)
105 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 */
123 public void
add_lnum(linenum,pos)124 add_lnum(linenum, pos)
125 LINENUM linenum;
126 POSITION pos;
127 {
128 struct linenum_info *p;
129 struct linenum_info *new;
130 struct linenum_info *nextp;
131 struct linenum_info *prevp;
132 POSITION mingap;
133
134 /*
135 * Find the proper place in the list for the new one.
136 * The entries are sorted by position.
137 */
138 for (p = anchor.next; p != &anchor && p->pos < pos; p = p->next)
139 if (p->line == linenum)
140 /* We already have this one. */
141 return;
142 nextp = p;
143 prevp = p->prev;
144
145 if (freelist != NULL)
146 {
147 /*
148 * We still have free (unused) entries.
149 * Use one of them.
150 */
151 new = freelist;
152 freelist = freelist->next;
153 } else
154 {
155 /*
156 * No free entries.
157 * Use the "spare" entry.
158 */
159 new = spare;
160 spare = NULL;
161 }
162
163 /*
164 * Fill in the fields of the new entry,
165 * and insert it into the proper place in the list.
166 */
167 new->next = nextp;
168 new->prev = prevp;
169 new->pos = pos;
170 new->line = linenum;
171
172 nextp->prev = new;
173 prevp->next = new;
174
175 /*
176 * Recalculate gaps for the new entry and the neighboring entries.
177 */
178 calcgap(new);
179 calcgap(nextp);
180 calcgap(prevp);
181
182 if (spare == NULL)
183 {
184 /*
185 * We have used the spare entry.
186 * Scan the list to find the one with the smallest
187 * gap, take it out and make it the spare.
188 * We should never remove the last one, so stop when
189 * we get to p->next == &anchor. This also avoids
190 * looking at the gap of the last one, which is
191 * not computed by calcgap.
192 */
193 mingap = anchor.next->gap;
194 for (p = anchor.next; p->next != &anchor; p = p->next)
195 {
196 if (p->gap <= mingap)
197 {
198 spare = p;
199 mingap = p->gap;
200 }
201 }
202 spare->next->prev = spare->prev;
203 spare->prev->next = spare->next;
204 }
205 }
206
207 /*
208 * If we get stuck in a long loop trying to figure out the
209 * line number, print a message to tell the user what we're doing.
210 */
211 static void
longloopmessage(VOID_PARAM)212 longloopmessage(VOID_PARAM)
213 {
214 ierror("Calculating line numbers", NULL_PARG);
215 }
216
217 static int loopcount;
218 #if HAVE_TIME
219 static time_type startime;
220 #endif
221
222 static void
longish(VOID_PARAM)223 longish(VOID_PARAM)
224 {
225 #if HAVE_TIME
226 if (loopcount >= 0 && ++loopcount > 100)
227 {
228 loopcount = 0;
229 if (get_time() >= startime + LONGTIME)
230 {
231 longloopmessage();
232 loopcount = -1;
233 }
234 }
235 #else
236 if (loopcount >= 0 && ++loopcount > LONGLOOP)
237 {
238 longloopmessage();
239 loopcount = -1;
240 }
241 #endif
242 }
243
244 /*
245 * Turn off line numbers because the user has interrupted
246 * a lengthy line number calculation.
247 */
248 static void
abort_long(VOID_PARAM)249 abort_long(VOID_PARAM)
250 {
251 if (loopcount >= 0)
252 return;
253 if (linenums == OPT_ONPLUS)
254 /*
255 * We were displaying line numbers, so need to repaint.
256 */
257 screen_trashed = 1;
258 linenums = 0;
259 error("Line numbers turned off", NULL_PARG);
260 }
261
262 /*
263 * Find the line number associated with a given position.
264 * Return 0 if we can't figure it out.
265 */
266 public LINENUM
find_linenum(pos)267 find_linenum(pos)
268 POSITION pos;
269 {
270 struct linenum_info *p;
271 LINENUM linenum;
272 POSITION cpos;
273
274 if (!linenums)
275 /*
276 * We're not using line numbers.
277 */
278 return (0);
279 if (pos == NULL_POSITION)
280 /*
281 * Caller doesn't know what he's talking about.
282 */
283 return (0);
284 if (pos <= ch_zero())
285 /*
286 * Beginning of file is always line number 1.
287 */
288 return (1);
289
290 /*
291 * Find the entry nearest to the position we want.
292 */
293 for (p = anchor.next; p != &anchor && p->pos < pos; p = p->next)
294 continue;
295 if (p->pos == pos)
296 /* Found it exactly. */
297 return (p->line);
298
299 /*
300 * This is the (possibly) time-consuming part.
301 * We start at the line we just found and start
302 * reading the file forward or backward till we
303 * get to the place we want.
304 *
305 * First decide whether we should go forward from the
306 * previous one or backwards from the next one.
307 * The decision is based on which way involves
308 * traversing fewer bytes in the file.
309 */
310 #if HAVE_TIME
311 startime = get_time();
312 #endif
313 loopcount = 0;
314 if (p == &anchor || pos - p->prev->pos < p->pos - pos)
315 {
316 /*
317 * Go forward.
318 */
319 p = p->prev;
320 if (ch_seek(p->pos))
321 return (0);
322 for (linenum = p->line, cpos = p->pos; cpos < pos; linenum++)
323 {
324 /*
325 * Allow a signal to abort this loop.
326 */
327 cpos = forw_raw_line(cpos, (char **)NULL, (int *)NULL);
328 if (ABORT_SIGS()) {
329 abort_long();
330 return (0);
331 }
332 if (cpos == NULL_POSITION)
333 return (0);
334 longish();
335 }
336 /*
337 * We might as well cache it.
338 */
339 add_lnum(linenum, cpos);
340 /*
341 * If the given position is not at the start of a line,
342 * make sure we return the correct line number.
343 */
344 if (cpos > pos)
345 linenum--;
346 } else
347 {
348 /*
349 * Go backward.
350 */
351 if (ch_seek(p->pos))
352 return (0);
353 for (linenum = p->line, cpos = p->pos; cpos > pos; linenum--)
354 {
355 /*
356 * Allow a signal to abort this loop.
357 */
358 cpos = back_raw_line(cpos, (char **)NULL, (int *)NULL);
359 if (ABORT_SIGS()) {
360 abort_long();
361 return (0);
362 }
363 if (cpos == NULL_POSITION)
364 return (0);
365 longish();
366 }
367 /*
368 * We might as well cache it.
369 */
370 add_lnum(linenum, cpos);
371 }
372 loopcount = 0;
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 */
380 public POSITION
find_pos(linenum)381 find_pos(linenum)
382 LINENUM linenum;
383 {
384 struct linenum_info *p;
385 POSITION cpos;
386 LINENUM clinenum;
387
388 if (linenum <= 1)
389 /*
390 * Line number 1 is beginning of file.
391 */
392 return (ch_zero());
393
394 /*
395 * Find the entry nearest to the line number we want.
396 */
397 for (p = anchor.next; p != &anchor && p->line < linenum; p = p->next)
398 continue;
399 if (p->line == linenum)
400 /* Found it exactly. */
401 return (p->pos);
402
403 if (p == &anchor || linenum - p->prev->line < p->line - linenum)
404 {
405 /*
406 * Go forward.
407 */
408 p = p->prev;
409 if (ch_seek(p->pos))
410 return (NULL_POSITION);
411 for (clinenum = p->line, cpos = p->pos; clinenum < linenum; clinenum++)
412 {
413 /*
414 * Allow a signal to abort this loop.
415 */
416 cpos = forw_raw_line(cpos, (char **)NULL, (int *)NULL);
417 if (ABORT_SIGS())
418 return (NULL_POSITION);
419 if (cpos == NULL_POSITION)
420 return (NULL_POSITION);
421 }
422 } else
423 {
424 /*
425 * Go backward.
426 */
427 if (ch_seek(p->pos))
428 return (NULL_POSITION);
429 for (clinenum = p->line, cpos = p->pos; clinenum > linenum; clinenum--)
430 {
431 /*
432 * Allow a signal to abort this loop.
433 */
434 cpos = back_raw_line(cpos, (char **)NULL, (int *)NULL);
435 if (ABORT_SIGS())
436 return (NULL_POSITION);
437 if (cpos == NULL_POSITION)
438 return (NULL_POSITION);
439 }
440 }
441 /*
442 * We might as well cache it.
443 */
444 add_lnum(clinenum, cpos);
445 return (cpos);
446 }
447
448 /*
449 * Return the line number of the "current" line.
450 * The argument "where" tells which line is to be considered
451 * the "current" line (e.g. TOP, BOTTOM, MIDDLE, etc).
452 */
453 public LINENUM
currline(where)454 currline(where)
455 int where;
456 {
457 POSITION pos;
458 POSITION len;
459 LINENUM linenum;
460
461 pos = position(where);
462 len = ch_length();
463 while (pos == NULL_POSITION && where >= 0 && where < sc_height)
464 pos = position(++where);
465 if (pos == NULL_POSITION)
466 pos = len;
467 linenum = find_linenum(pos);
468 if (pos == len)
469 linenum--;
470 return (linenum);
471 }
472
473 /*
474 * Scan entire file, counting line numbers.
475 */
476 public void
scan_eof(VOID_PARAM)477 scan_eof(VOID_PARAM)
478 {
479 POSITION pos = 0;
480 LINENUM linenum = 0;
481
482 if (ch_seek(0))
483 return;
484 ierror("Determining length of file", NULL_PARG);
485 while (pos != NULL_POSITION)
486 {
487 /* For efficiency, only add one every 256 line numbers. */
488 if ((linenum++ % 256) == 0)
489 add_lnum(linenum, pos);
490 pos = forw_raw_line(pos, (char **)NULL, (int *)NULL);
491 if (ABORT_SIGS())
492 break;
493 }
494 }
495