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 */
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(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
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(VOID_PARAM)
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(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
249abort_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
267find_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
381find_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
454currline(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