1 /*
2 * Copyright (C) 1984-2017 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()76 clr_linenum()
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()212 longloopmessage()
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()223 longish()
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()249 abort_long()
250 {
251 if (linenums == OPT_ONPLUS)
252 /*
253 * We were displaying line numbers, so need to repaint.
254 */
255 screen_trashed = 1;
256 linenums = 0;
257 error("Line numbers turned off", NULL_PARG);
258 }
259
260 /*
261 * Find the line number associated with a given position.
262 * Return 0 if we can't figure it out.
263 */
264 public LINENUM
find_linenum(pos)265 find_linenum(pos)
266 POSITION pos;
267 {
268 struct linenum_info *p;
269 LINENUM linenum;
270 POSITION cpos;
271
272 if (!linenums)
273 /*
274 * We're not using line numbers.
275 */
276 return (0);
277 if (pos == NULL_POSITION)
278 /*
279 * Caller doesn't know what he's talking about.
280 */
281 return (0);
282 if (pos <= ch_zero())
283 /*
284 * Beginning of file is always line number 1.
285 */
286 return (1);
287
288 /*
289 * Find the entry nearest to the position we want.
290 */
291 for (p = anchor.next; p != &anchor && p->pos < pos; p = p->next)
292 continue;
293 if (p->pos == pos)
294 /* Found it exactly. */
295 return (p->line);
296
297 /*
298 * This is the (possibly) time-consuming part.
299 * We start at the line we just found and start
300 * reading the file forward or backward till we
301 * get to the place we want.
302 *
303 * First decide whether we should go forward from the
304 * previous one or backwards from the next one.
305 * The decision is based on which way involves
306 * traversing fewer bytes in the file.
307 */
308 #if HAVE_TIME
309 startime = get_time();
310 #endif
311 if (p == &anchor || pos - p->prev->pos < p->pos - pos)
312 {
313 /*
314 * Go forward.
315 */
316 p = p->prev;
317 if (ch_seek(p->pos))
318 return (0);
319 loopcount = 0;
320 for (linenum = p->line, cpos = p->pos; cpos < pos; linenum++)
321 {
322 /*
323 * Allow a signal to abort this loop.
324 */
325 cpos = forw_raw_line(cpos, (char **)NULL, (int *)NULL);
326 if (ABORT_SIGS()) {
327 abort_long();
328 return (0);
329 }
330 if (cpos == NULL_POSITION)
331 return (0);
332 longish();
333 }
334 /*
335 * We might as well cache it.
336 */
337 add_lnum(linenum, cpos);
338 /*
339 * If the given position is not at the start of a line,
340 * make sure we return the correct line number.
341 */
342 if (cpos > pos)
343 linenum--;
344 } else
345 {
346 /*
347 * Go backward.
348 */
349 if (ch_seek(p->pos))
350 return (0);
351 loopcount = 0;
352 for (linenum = p->line, cpos = p->pos; cpos > pos; linenum--)
353 {
354 /*
355 * Allow a signal to abort this loop.
356 */
357 cpos = back_raw_line(cpos, (char **)NULL, (int *)NULL);
358 if (ABORT_SIGS()) {
359 abort_long();
360 return (0);
361 }
362 if (cpos == NULL_POSITION)
363 return (0);
364 longish();
365 }
366 /*
367 * We might as well cache it.
368 */
369 add_lnum(linenum, cpos);
370 }
371
372 return (linenum);
373 }
374
375 /*
376 * Find the position of a given line number.
377 * Return NULL_POSITION if we can't figure it out.
378 */
379 public POSITION
find_pos(linenum)380 find_pos(linenum)
381 LINENUM linenum;
382 {
383 struct linenum_info *p;
384 POSITION cpos;
385 LINENUM clinenum;
386
387 if (linenum <= 1)
388 /*
389 * Line number 1 is beginning of file.
390 */
391 return (ch_zero());
392
393 /*
394 * Find the entry nearest to the line number we want.
395 */
396 for (p = anchor.next; p != &anchor && p->line < linenum; p = p->next)
397 continue;
398 if (p->line == linenum)
399 /* Found it exactly. */
400 return (p->pos);
401
402 if (p == &anchor || linenum - p->prev->line < p->line - linenum)
403 {
404 /*
405 * Go forward.
406 */
407 p = p->prev;
408 if (ch_seek(p->pos))
409 return (NULL_POSITION);
410 for (clinenum = p->line, cpos = p->pos; clinenum < linenum; clinenum++)
411 {
412 /*
413 * Allow a signal to abort this loop.
414 */
415 cpos = forw_raw_line(cpos, (char **)NULL, (int *)NULL);
416 if (ABORT_SIGS())
417 return (NULL_POSITION);
418 if (cpos == NULL_POSITION)
419 return (NULL_POSITION);
420 }
421 } else
422 {
423 /*
424 * Go backward.
425 */
426 if (ch_seek(p->pos))
427 return (NULL_POSITION);
428 for (clinenum = p->line, cpos = p->pos; clinenum > linenum; clinenum--)
429 {
430 /*
431 * Allow a signal to abort this loop.
432 */
433 cpos = back_raw_line(cpos, (char **)NULL, (int *)NULL);
434 if (ABORT_SIGS())
435 return (NULL_POSITION);
436 if (cpos == NULL_POSITION)
437 return (NULL_POSITION);
438 }
439 }
440 /*
441 * We might as well cache it.
442 */
443 add_lnum(clinenum, cpos);
444 return (cpos);
445 }
446
447 /*
448 * Return the line number of the "current" line.
449 * The argument "where" tells which line is to be considered
450 * the "current" line (e.g. TOP, BOTTOM, MIDDLE, etc).
451 */
452 public LINENUM
currline(where)453 currline(where)
454 int where;
455 {
456 POSITION pos;
457 POSITION len;
458 LINENUM linenum;
459
460 pos = position(where);
461 len = ch_length();
462 while (pos == NULL_POSITION && where >= 0 && where < sc_height)
463 pos = position(++where);
464 if (pos == NULL_POSITION)
465 pos = len;
466 linenum = find_linenum(pos);
467 if (pos == len)
468 linenum--;
469 return (linenum);
470 }
471