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 */
41struct 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
62static struct linenum_info anchor;      /* Anchor of the list */
63static struct linenum_info *freelist;   /* Anchor of the unused entries */
64static struct linenum_info pool[NPOOL]; /* The pool itself */
65static struct linenum_info *spare;      /* We always keep one spare entry */
66public int scanning_eof = FALSE;
67
68extern int linenums;
69extern int sigs;
70extern int sc_height;
71extern int screen_trashed;
72extern int header_lines;
73extern int nonum_headers;
74
75/*
76 * Initialize the line number structures.
77 */
78public 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 */
105static 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 */
123public 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 */
208static void longloopmessage(void)
209{
210	ierror("Calculating line numbers", NULL_PARG);
211}
212
213static int loopcount;
214#if HAVE_TIME
215static time_type startime;
216#endif
217
218static 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 */
243static 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 */
260public 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 */
372public 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 */
443public 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 */
464public 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 */
493public LINENUM vlinenum(LINENUM linenum)
494{
495	if (nonum_headers)
496		linenum = (linenum < header_lines) ? 0 : linenum - header_lines;
497	return linenum;
498}
499