1/*	$NetBSD: linenum.c,v 1.3 2011/07/03 20:14:13 tron Exp $	*/
2
3/*
4 * Copyright (C) 1984-2011  Mark Nudelman
5 *
6 * You may distribute under the terms of either the GNU General Public
7 * License or the Less License, as specified in the README file.
8 *
9 * For more information about less, or for information on how to
10 * contact the author, see the README file.
11 */
12
13
14/*
15 * Code to handle displaying line numbers.
16 *
17 * Finding the line number of a given file position is rather tricky.
18 * We don't want to just start at the beginning of the file and
19 * count newlines, because that is slow for large files (and also
20 * wouldn't work if we couldn't get to the start of the file; e.g.
21 * if input is a long pipe).
22 *
23 * So we use the function add_lnum to cache line numbers.
24 * We try to be very clever and keep only the more interesting
25 * line numbers when we run out of space in our table.  A line
26 * number is more interesting than another when it is far from
27 * other line numbers.   For example, we'd rather keep lines
28 * 100,200,300 than 100,101,300.  200 is more interesting than
29 * 101 because 101 can be derived very cheaply from 100, while
30 * 200 is more expensive to derive from 100.
31 *
32 * The function currline() returns the line number of a given
33 * position in the file.  As a side effect, it calls add_lnum
34 * to cache the line number.  Therefore currline is occasionally
35 * called to make sure we cache line numbers often enough.
36 */
37
38#include "less.h"
39
40/*
41 * Structure to keep track of a line number and the associated file position.
42 * A doubly-linked circular list of line numbers is kept ordered by line number.
43 */
44struct linenum_info
45{
46	struct linenum_info *next;	/* Link to next in the list */
47	struct linenum_info *prev;	/* Line to previous in the list */
48	POSITION pos;			/* File position */
49	POSITION gap;			/* Gap between prev and next */
50	LINENUM line;			/* Line number */
51};
52/*
53 * "gap" needs some explanation: the gap of any particular line number
54 * is the distance between the previous one and the next one in the list.
55 * ("Distance" means difference in file position.)  In other words, the
56 * gap of a line number is the gap which would be introduced if this
57 * line number were deleted.  It is used to decide which one to replace
58 * when we have a new one to insert and the table is full.
59 */
60
61#define	NPOOL	200			/* Size of line number pool */
62
63#define	LONGTIME	(2)		/* In seconds */
64
65static struct linenum_info anchor;	/* Anchor of the list */
66static struct linenum_info *freelist;	/* Anchor of the unused entries */
67static struct linenum_info pool[NPOOL];	/* The pool itself */
68static struct linenum_info *spare;		/* We always keep one spare entry */
69
70extern int linenums;
71extern int sigs;
72extern int sc_height;
73extern int screen_trashed;
74
75static void calcgap __P((struct linenum_info *));
76static void longloopmessage __P((void));
77static void longish __P((void));
78
79/*
80 * Initialize the line number structures.
81 */
82	public void
83clr_linenum()
84{
85	register struct linenum_info *p;
86
87	/*
88	 * Put all the entries on the free list.
89	 * Leave one for the "spare".
90	 */
91	for (p = pool;  p < &pool[NPOOL-2];  p++)
92		p->next = p+1;
93	pool[NPOOL-2].next = NULL;
94	freelist = pool;
95
96	spare = &pool[NPOOL-1];
97
98	/*
99	 * Initialize the anchor.
100	 */
101	anchor.next = anchor.prev = &anchor;
102	anchor.gap = 0;
103	anchor.pos = (POSITION)0;
104	anchor.line = 1;
105}
106
107/*
108 * Calculate the gap for an entry.
109 */
110	static void
111calcgap(p)
112	register struct linenum_info *p;
113{
114	/*
115	 * Don't bother to compute a gap for the anchor.
116	 * Also don't compute a gap for the last one in the list.
117	 * The gap for that last one should be considered infinite,
118	 * but we never look at it anyway.
119	 */
120	if (p == &anchor || p->next == &anchor)
121		return;
122	p->gap = p->next->pos - p->prev->pos;
123}
124
125/*
126 * Add a new line number to the cache.
127 * The specified position (pos) should be the file position of the
128 * FIRST character in the specified line.
129 */
130	public void
131add_lnum(linenum, pos)
132	LINENUM linenum;
133	POSITION pos;
134{
135	register struct linenum_info *p;
136	register struct linenum_info *new;
137	register struct linenum_info *nextp;
138	register struct linenum_info *prevp;
139	register POSITION mingap;
140
141	/*
142	 * Find the proper place in the list for the new one.
143	 * The entries are sorted by position.
144	 */
145	for (p = anchor.next;  p != &anchor && p->pos < pos;  p = p->next)
146		if (p->line == linenum)
147			/* We already have this one. */
148			return;
149	nextp = p;
150	prevp = p->prev;
151
152	if (freelist != NULL)
153	{
154		/*
155		 * We still have free (unused) entries.
156		 * Use one of them.
157		 */
158		new = freelist;
159		freelist = freelist->next;
160	} else
161	{
162		/*
163		 * No free entries.
164		 * Use the "spare" entry.
165		 */
166		new = spare;
167		spare = NULL;
168	}
169
170	/*
171	 * Fill in the fields of the new entry,
172	 * and insert it into the proper place in the list.
173	 */
174	new->next = nextp;
175	new->prev = prevp;
176	new->pos = pos;
177	new->line = linenum;
178
179	nextp->prev = new;
180	prevp->next = new;
181
182	/*
183	 * Recalculate gaps for the new entry and the neighboring entries.
184	 */
185	calcgap(new);
186	calcgap(nextp);
187	calcgap(prevp);
188
189	if (spare == NULL)
190	{
191		/*
192		 * We have used the spare entry.
193		 * Scan the list to find the one with the smallest
194		 * gap, take it out and make it the spare.
195		 * We should never remove the last one, so stop when
196		 * we get to p->next == &anchor.  This also avoids
197		 * looking at the gap of the last one, which is
198		 * not computed by calcgap.
199		 */
200		mingap = anchor.next->gap;
201		for (p = anchor.next;  p->next != &anchor;  p = p->next)
202		{
203			if (p->gap <= mingap)
204			{
205				spare = p;
206				mingap = p->gap;
207			}
208		}
209		spare->next->prev = spare->prev;
210		spare->prev->next = spare->next;
211	}
212}
213
214/*
215 * If we get stuck in a long loop trying to figure out the
216 * line number, print a message to tell the user what we're doing.
217 */
218	static void
219longloopmessage()
220{
221	ierror("Calculating line numbers", NULL_PARG);
222}
223
224static int loopcount;
225#if HAVE_TIME
226static long startime;
227#endif
228
229	static void
230longish()
231{
232#if HAVE_TIME
233	if (loopcount >= 0 && ++loopcount > 100)
234	{
235		loopcount = 0;
236		if (get_time() >= startime + LONGTIME)
237		{
238			longloopmessage();
239			loopcount = -1;
240		}
241	}
242#else
243	if (loopcount >= 0 && ++loopcount > LONGLOOP)
244	{
245		longloopmessage();
246		loopcount = -1;
247	}
248#endif
249}
250
251/*
252 * Turn off line numbers because the user has interrupted
253 * a lengthy line number calculation.
254 */
255	static void
256abort_long()
257{
258	if (linenums == OPT_ONPLUS)
259		/*
260		 * We were displaying line numbers, so need to repaint.
261		 */
262		screen_trashed = 1;
263	linenums = 0;
264	error("Line numbers turned off", NULL_PARG);
265}
266
267/*
268 * Find the line number associated with a given position.
269 * Return 0 if we can't figure it out.
270 */
271	public LINENUM
272find_linenum(pos)
273	POSITION pos;
274{
275	register struct linenum_info *p;
276	register LINENUM linenum;
277	POSITION cpos;
278
279	if (!linenums)
280		/*
281		 * We're not using line numbers.
282		 */
283		return (0);
284	if (pos == NULL_POSITION)
285		/*
286		 * Caller doesn't know what he's talking about.
287		 */
288		return (0);
289	if (pos <= ch_zero())
290		/*
291		 * Beginning of file is always line number 1.
292		 */
293		return (1);
294
295	/*
296	 * Find the entry nearest to the position we want.
297	 */
298	for (p = anchor.next;  p != &anchor && p->pos < pos;  p = p->next)
299		continue;
300	if (p->pos == pos)
301		/* Found it exactly. */
302		return (p->line);
303
304	/*
305	 * This is the (possibly) time-consuming part.
306	 * We start at the line we just found and start
307	 * reading the file forward or backward till we
308	 * get to the place we want.
309	 *
310	 * First decide whether we should go forward from the
311	 * previous one or backwards from the next one.
312	 * The decision is based on which way involves
313	 * traversing fewer bytes in the file.
314	 */
315#if HAVE_TIME
316	startime = get_time();
317#endif
318	if (p == &anchor || pos - p->prev->pos < p->pos - pos)
319	{
320		/*
321		 * Go forward.
322		 */
323		p = p->prev;
324		if (ch_seek(p->pos))
325			return (0);
326		loopcount = 0;
327		for (linenum = p->line, cpos = p->pos;  cpos < pos;  linenum++)
328		{
329			/*
330			 * Allow a signal to abort this loop.
331			 */
332			cpos = forw_raw_line(cpos, (char **)NULL, (int *)NULL);
333			if (ABORT_SIGS()) {
334				abort_long();
335				return (0);
336			}
337			if (cpos == NULL_POSITION)
338				return (0);
339			longish();
340		}
341		/*
342		 * We might as well cache it.
343		 */
344		add_lnum(linenum, cpos);
345		/*
346		 * If the given position is not at the start of a line,
347		 * make sure we return the correct line number.
348		 */
349		if (cpos > pos)
350			linenum--;
351	} else
352	{
353		/*
354		 * Go backward.
355		 */
356		if (ch_seek(p->pos))
357			return (0);
358		loopcount = 0;
359		for (linenum = p->line, cpos = p->pos;  cpos > pos;  linenum--)
360		{
361			/*
362			 * Allow a signal to abort this loop.
363			 */
364			cpos = back_raw_line(cpos, (char **)NULL, (int *)NULL);
365			if (ABORT_SIGS()) {
366				abort_long();
367				return (0);
368			}
369			if (cpos == NULL_POSITION)
370				return (0);
371			longish();
372		}
373		/*
374		 * We might as well cache it.
375		 */
376		add_lnum(linenum, cpos);
377	}
378
379	return (linenum);
380}
381
382/*
383 * Find the position of a given line number.
384 * Return NULL_POSITION if we can't figure it out.
385 */
386	public POSITION
387find_pos(linenum)
388	LINENUM linenum;
389{
390	register struct linenum_info *p;
391	POSITION cpos;
392	LINENUM clinenum;
393
394	if (linenum <= 1)
395		/*
396		 * Line number 1 is beginning of file.
397		 */
398		return (ch_zero());
399
400	/*
401	 * Find the entry nearest to the line number we want.
402	 */
403	for (p = anchor.next;  p != &anchor && p->line < linenum;  p = p->next)
404		continue;
405	if (p->line == linenum)
406		/* Found it exactly. */
407		return (p->pos);
408
409	if (p == &anchor || linenum - p->prev->line < p->line - linenum)
410	{
411		/*
412		 * Go forward.
413		 */
414		p = p->prev;
415		if (ch_seek(p->pos))
416			return (NULL_POSITION);
417		for (clinenum = p->line, cpos = p->pos;  clinenum < linenum;  clinenum++)
418		{
419			/*
420			 * Allow a signal to abort this loop.
421			 */
422			cpos = forw_raw_line(cpos, (char **)NULL, (int *)NULL);
423			if (ABORT_SIGS())
424				return (NULL_POSITION);
425			if (cpos == NULL_POSITION)
426				return (NULL_POSITION);
427		}
428	} else
429	{
430		/*
431		 * Go backward.
432		 */
433		if (ch_seek(p->pos))
434			return (NULL_POSITION);
435		for (clinenum = p->line, cpos = p->pos;  clinenum > linenum;  clinenum--)
436		{
437			/*
438			 * Allow a signal to abort this loop.
439			 */
440			cpos = back_raw_line(cpos, (char **)NULL, (int *)NULL);
441			if (ABORT_SIGS())
442				return (NULL_POSITION);
443			if (cpos == NULL_POSITION)
444				return (NULL_POSITION);
445		}
446	}
447	/*
448	 * We might as well cache it.
449	 */
450	add_lnum(clinenum, cpos);
451	return (cpos);
452}
453
454/*
455 * Return the line number of the "current" line.
456 * The argument "where" tells which line is to be considered
457 * the "current" line (e.g. TOP, BOTTOM, MIDDLE, etc).
458 */
459	public LINENUM
460currline(where)
461	int where;
462{
463	POSITION pos;
464	POSITION len;
465	LINENUM linenum;
466
467	pos = position(where);
468	len = ch_length();
469	while (pos == NULL_POSITION && where >= 0 && where < sc_height)
470		pos = position(++where);
471	if (pos == NULL_POSITION)
472		pos = len;
473	linenum = find_linenum(pos);
474	if (pos == len)
475		linenum--;
476	return (linenum);
477}
478