NetBSD-5.0.2/distrib/utils/more/linenum.c
/* $NetBSD: linenum.c,v 1.5 2003/10/13 14:34:25 agc Exp $ */
/*
* Copyright (c) 1988 Mark Nudelman
* Copyright (c) 1988, 1993
* The Regents of the University of California. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. Neither the name of the University nor the names of its contributors
* may be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*/
#include <sys/cdefs.h>
#ifndef lint
#if 0
static char sccsid[] = "@(#)linenum.c 8.1 (Berkeley) 6/6/93";
#else
__RCSID("$NetBSD: linenum.c,v 1.5 2003/10/13 14:34:25 agc Exp $");
#endif
#endif /* not lint */
/*
* 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 <sys/types.h>
#include <stdio.h>
#include <time.h>
#include "less.h"
#include "extern.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
{
struct linenum *next; /* Link to next in the list */
struct linenum *prev; /* Line to previous in the list */
off_t pos; /* File position */
off_t gap; /* Gap between prev and next */
int 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 50 /* Size of line number pool */
#define LONGTIME (2) /* In seconds */
int lnloop = 0; /* Are we in the line num loop? */
static struct linenum anchor; /* Anchor of the list */
static struct linenum *freelist; /* Anchor of the unused entries */
static struct linenum pool[NPOOL]; /* The pool itself */
static struct linenum *spare; /* We always keep one spare entry */
static void calcgap __P((struct linenum *));
static void longloopmessage __P((void));
/*
* Initialize the line number structures.
*/
void
clr_linenum()
{
struct linenum *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;
spare = &pool[NPOOL-1];
/*
* Initialize the anchor.
*/
anchor.next = anchor.prev = &anchor;
anchor.gap = 0;
anchor.pos = (off_t)0;
anchor.line = 1;
}
/*
* Calculate the gap for an entry.
*/
static void
calcgap(p)
struct linenum *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.
*/
void
add_lnum(line, pos)
int line;
off_t pos;
{
struct linenum *p;
struct linenum *new;
struct linenum *nextp;
struct linenum *prevp;
off_t 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 == line)
/* 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 = line;
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()
{
ierror("Calculating line numbers");
/*
* Set the lnloop flag here, so if the user interrupts while
* we are calculating line numbers, the signal handler will
* turn off line numbers (linenums=0).
*/
lnloop = 1;
}
/*
* Find the line number associated with a given position.
* Return 0 if we can't figure it out.
*/
int
find_linenum(pos)
off_t pos;
{
struct linenum *p;
int lno;
int loopcount;
off_t cpos;
time_t startime;
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 == (off_t)0)
/*
* 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.
*/
flush();
(void)time(&startime);
if (p == &anchor || pos - p->prev->pos < p->pos - pos)
{
/*
* Go forward.
*/
p = p->prev;
if (ch_seek(p->pos))
return (0);
loopcount = 0;
for (lno = p->line, cpos = p->pos; cpos < pos; lno++)
{
/*
* Allow a signal to abort this loop.
*/
cpos = forw_raw_line(cpos);
if (sigs || cpos == NULL_POSITION)
return (0);
if (loopcount >= 0 && ++loopcount > 100) {
loopcount = 0;
if (time((time_t *)NULL)
>= startime + LONGTIME) {
longloopmessage();
loopcount = -1;
}
}
}
lnloop = 0;
/*
* If the given position is not at the start of a line,
* make sure we return the correct line number.
*/
if (cpos > pos)
lno--;
} else
{
/*
* Go backward.
*/
if (ch_seek(p->pos))
return (0);
loopcount = 0;
for (lno = p->line, cpos = p->pos; cpos > pos; lno--)
{
/*
* Allow a signal to abort this loop.
*/
cpos = back_raw_line(cpos);
if (sigs || cpos == NULL_POSITION)
return (0);
if (loopcount >= 0 && ++loopcount > 100) {
loopcount = 0;
if (time((time_t *)NULL)
>= startime + LONGTIME) {
longloopmessage();
loopcount = -1;
}
}
}
lnloop = 0;
}
/*
* We might as well cache it.
*/
add_lnum(lno, cpos);
return (lno);
}
/*
* 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).
*/
int
currline(where)
int where;
{
off_t pos;
if ((pos = position(where)) == NULL_POSITION)
pos = ch_length();
return(find_linenum(pos));
}