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 */
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 */
66
67extern int linenums;
68extern int sigs;
69extern int sc_height;
70extern int screen_trashed;
71
72/*
73 * Initialize the line number structures.
74 */
75	public void
76clr_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
104calcgap(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
124add_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
212longloopmessage()
213{
214	ierror("Calculating line numbers", NULL_PARG);
215}
216
217static int loopcount;
218#if HAVE_TIME
219static time_type startime;
220#endif
221
222	static void
223longish()
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
249abort_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
265find_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
380find_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
453currline(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