2 * Copyright (C) 1984-2011 Mark Nudelman
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.
7 * For more information about less, or for information on how to
8 * contact the author, see the README file.
13 * Code to handle displaying line numbers.
15 * Finding the line number of a given file position is rather tricky.
16 * We don't want to just start at the beginning of the file and
17 * count newlines, because that is slow for large files (and also
18 * wouldn't work if we couldn't get to the start of the file; e.g.
19 * if input is a long pipe).
21 * So we use the function add_lnum to cache line numbers.
22 * We try to be very clever and keep only the more interesting
23 * line numbers when we run out of space in our table. A line
24 * number is more interesting than another when it is far from
25 * other line numbers. For example, we'd rather keep lines
26 * 100,200,300 than 100,101,300. 200 is more interesting than
27 * 101 because 101 can be derived very cheaply from 100, while
28 * 200 is more expensive to derive from 100.
30 * The function currline() returns the line number of a given
31 * position in the file. As a side effect, it calls add_lnum
32 * to cache the line number. Therefore currline is occasionally
33 * called to make sure we cache line numbers often enough.
39 * Structure to keep track of a line number and the associated file position.
40 * A doubly-linked circular list of line numbers is kept ordered by line number.
44 struct linenum_info *next; /* Link to next in the list */
45 struct linenum_info *prev; /* Line to previous in the list */
46 POSITION pos; /* File position */
47 POSITION gap; /* Gap between prev and next */
48 LINENUM line; /* Line number */
51 * "gap" needs some explanation: the gap of any particular line number
52 * is the distance between the previous one and the next one in the list.
53 * ("Distance" means difference in file position.) In other words, the
54 * gap of a line number is the gap which would be introduced if this
55 * line number were deleted. It is used to decide which one to replace
56 * when we have a new one to insert and the table is full.
59 #define NPOOL 200 /* Size of line number pool */
61 #define LONGTIME (2) /* In seconds */
63 static struct linenum_info anchor; /* Anchor of the list */
64 static struct linenum_info *freelist; /* Anchor of the unused entries */
65 static struct linenum_info pool[NPOOL]; /* The pool itself */
66 static struct linenum_info *spare; /* We always keep one spare entry */
71 extern int screen_trashed;
74 * Initialize the line number structures.
79 register struct linenum_info *p;
82 * Put all the entries on the free list.
83 * Leave one for the "spare".
85 for (p = pool; p < &pool[NPOOL-2]; p++)
87 pool[NPOOL-2].next = NULL;
90 spare = &pool[NPOOL-1];
93 * Initialize the anchor.
95 anchor.next = anchor.prev = &anchor;
97 anchor.pos = (POSITION)0;
102 * Calculate the gap for an entry.
106 register struct linenum_info *p;
109 * Don't bother to compute a gap for the anchor.
110 * Also don't compute a gap for the last one in the list.
111 * The gap for that last one should be considered infinite,
112 * but we never look at it anyway.
114 if (p == &anchor || p->next == &anchor)
116 p->gap = p->next->pos - p->prev->pos;
120 * Add a new line number to the cache.
121 * The specified position (pos) should be the file position of the
122 * FIRST character in the specified line.
125 add_lnum(linenum, pos)
129 register struct linenum_info *p;
130 register struct linenum_info *new;
131 register struct linenum_info *nextp;
132 register struct linenum_info *prevp;
133 register POSITION mingap;
136 * Find the proper place in the list for the new one.
137 * The entries are sorted by position.
139 for (p = anchor.next; p != &anchor && p->pos < pos; p = p->next)
140 if (p->line == linenum)
141 /* We already have this one. */
146 if (freelist != NULL)
149 * We still have free (unused) entries.
153 freelist = freelist->next;
158 * Use the "spare" entry.
165 * Fill in the fields of the new entry,
166 * and insert it into the proper place in the list.
177 * Recalculate gaps for the new entry and the neighboring entries.
186 * We have used the spare entry.
187 * Scan the list to find the one with the smallest
188 * gap, take it out and make it the spare.
189 * We should never remove the last one, so stop when
190 * we get to p->next == &anchor. This also avoids
191 * looking at the gap of the last one, which is
192 * not computed by calcgap.
194 mingap = anchor.next->gap;
195 for (p = anchor.next; p->next != &anchor; p = p->next)
197 if (p->gap <= mingap)
203 spare->next->prev = spare->prev;
204 spare->prev->next = spare->next;
209 * If we get stuck in a long loop trying to figure out the
210 * line number, print a message to tell the user what we're doing.
215 ierror("Calculating line numbers", NULL_PARG);
218 static int loopcount;
220 static long startime;
227 if (loopcount >= 0 && ++loopcount > 100)
230 if (get_time() >= startime + LONGTIME)
237 if (loopcount >= 0 && ++loopcount > LONGLOOP)
246 * Turn off line numbers because the user has interrupted
247 * a lengthy line number calculation.
252 if (linenums == OPT_ONPLUS)
254 * We were displaying line numbers, so need to repaint.
258 error("Line numbers turned off", NULL_PARG);
262 * Find the line number associated with a given position.
263 * Return 0 if we can't figure it out.
269 register struct linenum_info *p;
270 register LINENUM linenum;
275 * We're not using line numbers.
278 if (pos == NULL_POSITION)
280 * Caller doesn't know what he's talking about.
283 if (pos <= ch_zero())
285 * Beginning of file is always line number 1.
290 * Find the entry nearest to the position we want.
292 for (p = anchor.next; p != &anchor && p->pos < pos; p = p->next)
295 /* Found it exactly. */
299 * This is the (possibly) time-consuming part.
300 * We start at the line we just found and start
301 * reading the file forward or backward till we
302 * get to the place we want.
304 * First decide whether we should go forward from the
305 * previous one or backwards from the next one.
306 * The decision is based on which way involves
307 * traversing fewer bytes in the file.
310 startime = get_time();
312 if (p == &anchor || pos - p->prev->pos < p->pos - pos)
321 for (linenum = p->line, cpos = p->pos; cpos < pos; linenum++)
324 * Allow a signal to abort this loop.
326 cpos = forw_raw_line(cpos, (char **)NULL, (int *)NULL);
331 if (cpos == NULL_POSITION)
336 * We might as well cache it.
338 add_lnum(linenum, cpos);
340 * If the given position is not at the start of a line,
341 * make sure we return the correct line number.
353 for (linenum = p->line, cpos = p->pos; cpos > pos; linenum--)
356 * Allow a signal to abort this loop.
358 cpos = back_raw_line(cpos, (char **)NULL, (int *)NULL);
363 if (cpos == NULL_POSITION)
368 * We might as well cache it.
370 add_lnum(linenum, cpos);
377 * Find the position of a given line number.
378 * Return NULL_POSITION if we can't figure it out.
384 register struct linenum_info *p;
390 * Line number 1 is beginning of file.
395 * Find the entry nearest to the line number we want.
397 for (p = anchor.next; p != &anchor && p->line < linenum; p = p->next)
399 if (p->line == linenum)
400 /* Found it exactly. */
403 if (p == &anchor || linenum - p->prev->line < p->line - linenum)
410 return (NULL_POSITION);
411 for (clinenum = p->line, cpos = p->pos; clinenum < linenum; clinenum++)
414 * Allow a signal to abort this loop.
416 cpos = forw_raw_line(cpos, (char **)NULL, (int *)NULL);
418 return (NULL_POSITION);
419 if (cpos == NULL_POSITION)
420 return (NULL_POSITION);
428 return (NULL_POSITION);
429 for (clinenum = p->line, cpos = p->pos; clinenum > linenum; clinenum--)
432 * Allow a signal to abort this loop.
434 cpos = back_raw_line(cpos, (char **)NULL, (int *)NULL);
436 return (NULL_POSITION);
437 if (cpos == NULL_POSITION)
438 return (NULL_POSITION);
442 * We might as well cache it.
444 add_lnum(clinenum, cpos);
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).
461 pos = position(where);
463 while (pos == NULL_POSITION && where >= 0 && where < sc_height)
464 pos = position(++where);
465 if (pos == NULL_POSITION)
467 linenum = find_linenum(pos);