2 * Copyright (C) 1984-2009 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
);