/*
* Copyright (C) 1984-2023 Mark Nudelman
*
* You may distribute under the terms of either the GNU General Public
* License or the Less License, as specified in the README file.
*
* For more information, see the README file.
*/
/*
* Code to handle displaying line numbers.
*
* Finding the line number of a given file position is rather tricky.
* We don't want to just start at the beginning of the file and
* count newlines, because that is slow for large files (and also
* wouldn't work if we couldn't get to the start of the file; e.g.
* if input is a long pipe).
*
* So we use the function add_lnum to cache line numbers.
* We try to be very clever and keep only the more interesting
* line numbers when we run out of space in our table. A line
* number is more interesting than another when it is far from
* other line numbers. For example, we'd rather keep lines
* 100,200,300 than 100,101,300. 200 is more interesting than
* 101 because 101 can be derived very cheaply from 100, while
* 200 is more expensive to derive from 100.
*
* The function currline() returns the line number of a given
* position in the file. As a side effect, it calls add_lnum
* to cache the line number. Therefore currline is occasionally
* called to make sure we cache line numbers often enough.
*/
#include "less.h"
/*
* Structure to keep track of a line number and the associated file position.
* A doubly-linked circular list of line numbers is kept ordered by line number.
*/
struct linenum_info
{
struct linenum_info *next; /* Link to next in the list */
struct linenum_info *prev; /* Line to previous in the list */
POSITION pos; /* File position */
POSITION gap; /* Gap between prev and next */
LINENUM line; /* Line number */
};
/*
* "gap" needs some explanation: the gap of any particular line number
* is the distance between the previous one and the next one in the list.
* ("Distance" means difference in file position.) In other words, the
* gap of a line number is the gap which would be introduced if this
* line number were deleted. It is used to decide which one to replace
* when we have a new one to insert and the table is full.
*/
#define NPOOL 200 /* Size of line number pool */
#define LONGTIME (2) /* In seconds */
static struct linenum_info anchor; /* Anchor of the list */
static struct linenum_info *freelist; /* Anchor of the unused entries */
static struct linenum_info pool[NPOOL]; /* The pool itself */
static struct linenum_info *spare; /* We always keep one spare entry */
public int scanning_eof = FALSE;
extern int linenums;
extern int sigs;
extern int sc_height;
extern int screen_trashed;
extern int header_lines;
extern int nonum_headers;
/*
* Initialize the line number structures.
*/
public void clr_linenum(void)
{
struct linenum_info *p;
/*
* Put all the entries on the free list.
* Leave one for the "spare".
*/
for (p = pool; p < &pool[NPOOL-2]; p++)
p->next = p+1;
pool[NPOOL-2].next = NULL;
freelist = pool;
/*
* Calculate the gap for an entry.
*/
static void calcgap(struct linenum_info *p)
{
/*
* Don't bother to compute a gap for the anchor.
* Also don't compute a gap for the last one in the list.
* The gap for that last one should be considered infinite,
* but we never look at it anyway.
*/
if (p == &anchor || p->next == &anchor)
return;
p->gap = p->next->pos - p->prev->pos;
}
/*
* Add a new line number to the cache.
* The specified position (pos) should be the file position of the
* FIRST character in the specified line.
*/
public void add_lnum(LINENUM linenum, POSITION pos)
{
struct linenum_info *p;
struct linenum_info *new;
struct linenum_info *nextp;
struct linenum_info *prevp;
POSITION mingap;
/*
* Find the proper place in the list for the new one.
* The entries are sorted by position.
*/
for (p = anchor.next; p != &anchor && p->pos < pos; p = p->next)
if (p->line == linenum)
/* We already have this one. */
return;
nextp = p;
prevp = p->prev;
if (freelist != NULL)
{
/*
* We still have free (unused) entries.
* Use one of them.
*/
new = freelist;
freelist = freelist->next;
} else
{
/*
* No free entries.
* Use the "spare" entry.
*/
new = spare;
spare = NULL;
}
/*
* Fill in the fields of the new entry,
* and insert it into the proper place in the list.
*/
new->next = nextp;
new->prev = prevp;
new->pos = pos;
new->line = linenum;
nextp->prev = new;
prevp->next = new;
/*
* Recalculate gaps for the new entry and the neighboring entries.
*/
calcgap(new);
calcgap(nextp);
calcgap(prevp);
if (spare == NULL)
{
/*
* We have used the spare entry.
* Scan the list to find the one with the smallest
* gap, take it out and make it the spare.
* We should never remove the last one, so stop when
* we get to p->next == &anchor. This also avoids
* looking at the gap of the last one, which is
* not computed by calcgap.
*/
mingap = anchor.next->gap;
for (p = anchor.next; p->next != &anchor; p = p->next)
{
if (p->gap <= mingap)
{
spare = p;
mingap = p->gap;
}
}
spare->next->prev = spare->prev;
spare->prev->next = spare->next;
}
}
/*
* If we get stuck in a long loop trying to figure out the
* line number, print a message to tell the user what we're doing.
*/
static void longloopmessage(void)
{
ierror("Calculating line numbers", NULL_PARG);
}
static int loopcount;
#if HAVE_TIME
static time_type startime;
#endif
/*
* Turn off line numbers because the user has interrupted
* a lengthy line number calculation.
*/
static void abort_long(void)
{
if (loopcount >= 0)
return;
if (linenums == OPT_ONPLUS)
/*
* We were displaying line numbers, so need to repaint.
*/
screen_trashed = 1;
linenums = 0;
error("Line numbers turned off", NULL_PARG);
}
/*
* Find the line number associated with a given position.
* Return 0 if we can't figure it out.
*/
public LINENUM find_linenum(POSITION pos)
{
struct linenum_info *p;
LINENUM linenum;
POSITION cpos;
if (!linenums)
/*
* We're not using line numbers.
*/
return (0);
if (pos == NULL_POSITION)
/*
* Caller doesn't know what he's talking about.
*/
return (0);
if (pos <= ch_zero())
/*
* Beginning of file is always line number 1.
*/
return (1);
/*
* Find the entry nearest to the position we want.
*/
for (p = anchor.next; p != &anchor && p->pos < pos; p = p->next)
continue;
if (p->pos == pos)
/* Found it exactly. */
return (p->line);
/*
* This is the (possibly) time-consuming part.
* We start at the line we just found and start
* reading the file forward or backward till we
* get to the place we want.
*
* First decide whether we should go forward from the
* previous one or backwards from the next one.
* The decision is based on which way involves
* traversing fewer bytes in the file.
*/
#if HAVE_TIME
startime = get_time();
#endif
loopcount = 0;
if (p == &anchor || pos - p->prev->pos < p->pos - pos)
{
/*
* Go forward.
*/
p = p->prev;
if (ch_seek(p->pos))
return (0);
for (linenum = p->line, cpos = p->pos; cpos < pos; linenum++)
{
/*
* Allow a signal to abort this loop.
*/
cpos = forw_raw_line(cpos, (char **)NULL, (int *)NULL);
if (ABORT_SIGS()) {
abort_long();
return (0);
}
if (cpos == NULL_POSITION)
return (0);
longish();
}
/*
* We might as well cache it.
*/
add_lnum(linenum, cpos);
/*
* If the given position is not at the start of a line,
* make sure we return the correct line number.
*/
if (cpos > pos)
linenum--;
} else
{
/*
* Go backward.
*/
if (ch_seek(p->pos))
return (0);
for (linenum = p->line, cpos = p->pos; cpos > pos; linenum--)
{
/*
* Allow a signal to abort this loop.
*/
cpos = back_raw_line(cpos, (char **)NULL, (int *)NULL);
if (ABORT_SIGS()) {
abort_long();
return (0);
}
if (cpos == NULL_POSITION)
return (0);
longish();
}
/*
* We might as well cache it.
*/
add_lnum(linenum, cpos);
}
loopcount = 0;
return (linenum);
}
/*
* Find the position of a given line number.
* Return NULL_POSITION if we can't figure it out.
*/
public POSITION find_pos(LINENUM linenum)
{
struct linenum_info *p;
POSITION cpos;
LINENUM clinenum;
if (linenum <= 1)
/*
* Line number 1 is beginning of file.
*/
return (ch_zero());
/*
* Find the entry nearest to the line number we want.
*/
for (p = anchor.next; p != &anchor && p->line < linenum; p = p->next)
continue;
if (p->line == linenum)
/* Found it exactly. */
return (p->pos);
if (p == &anchor || linenum - p->prev->line < p->line - linenum)
{
/*
* Go forward.
*/
p = p->prev;
if (ch_seek(p->pos))
return (NULL_POSITION);
for (clinenum = p->line, cpos = p->pos; clinenum < linenum; clinenum++)
{
/*
* Allow a signal to abort this loop.
*/
cpos = forw_raw_line(cpos, (char **)NULL, (int *)NULL);
if (ABORT_SIGS())
return (NULL_POSITION);
if (cpos == NULL_POSITION)
return (NULL_POSITION);
}
} else
{
/*
* Go backward.
*/
if (ch_seek(p->pos))
return (NULL_POSITION);
for (clinenum = p->line, cpos = p->pos; clinenum > linenum; clinenum--)
{
/*
* Allow a signal to abort this loop.
*/
cpos = back_raw_line(cpos, (char **)NULL, (int *)NULL);
if (ABORT_SIGS())
return (NULL_POSITION);
if (cpos == NULL_POSITION)
return (NULL_POSITION);
}
}
/*
* We might as well cache it.
*/
add_lnum(clinenum, cpos);
return (cpos);
}
/*
* Return the line number of the "current" line.
* The argument "where" tells which line is to be considered
* the "current" line (e.g. TOP, BOTTOM, MIDDLE, etc).
*/
public LINENUM currline(int where)
{
POSITION pos;
POSITION len;
LINENUM linenum;
pos = position(where);
len = ch_length();
while (pos == NULL_POSITION && where >= 0 && where < sc_height)
pos = position(++where);
if (pos == NULL_POSITION)
pos = len;
linenum = find_linenum(pos);
if (pos == len)
linenum--;
return (linenum);
}
/*
* Scan entire file, counting line numbers.
*/
public void scan_eof(void)
{
POSITION pos = ch_zero();
LINENUM linenum = 0;
if (ch_seek(0))
return;
ierror("Determining length of file", NULL_PARG);
/*
* scanning_eof prevents the "Waiting for data" message from
* overwriting "Determining length of file".
*/
scanning_eof = TRUE;
while (pos != NULL_POSITION)
{
/* For efficiency, only add one every 256 line numbers. */
if ((linenum++ % 256) == 0)
add_lnum(linenum, pos);
pos = forw_raw_line(pos, (char **)NULL, (int *)NULL);
if (ABORT_SIGS())
break;
}
scanning_eof = FALSE;
}
/*
* Return a line number adjusted for display
* (handles the --no-number-headers option).
*/
public LINENUM vlinenum(LINENUM linenum)
{
if (nonum_headers)
linenum = (linenum < header_lines) ? 0 : linenum - header_lines;
return linenum;
}
