453 lines
10 KiB
C
453 lines
10 KiB
C
/*
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* Copyright (C) 1984-2002 Mark Nudelman
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*
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* You may distribute under the terms of either the GNU General Public
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* License or the Less License, as specified in the README file.
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*
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* For more information about less, or for information on how to
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* contact the author, see the README file.
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*/
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/*
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* Code to handle displaying line numbers.
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*
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* Finding the line number of a given file position is rather tricky.
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* We don't want to just start at the beginning of the file and
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* count newlines, because that is slow for large files (and also
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* wouldn't work if we couldn't get to the start of the file; e.g.
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* if input is a long pipe).
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*
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* So we use the function add_lnum to cache line numbers.
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* We try to be very clever and keep only the more interesting
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* line numbers when we run out of space in our table. A line
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* number is more interesting than another when it is far from
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* other line numbers. For example, we'd rather keep lines
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* 100,200,300 than 100,101,300. 200 is more interesting than
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* 101 because 101 can be derived very cheaply from 100, while
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* 200 is more expensive to derive from 100.
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*
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* The function currline() returns the line number of a given
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* position in the file. As a side effect, it calls add_lnum
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* to cache the line number. Therefore currline is occasionally
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* called to make sure we cache line numbers often enough.
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*/
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#include "less.h"
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/*
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* Structure to keep track of a line number and the associated file position.
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* A doubly-linked circular list of line numbers is kept ordered by line number.
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*/
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struct linenum_info
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{
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struct linenum_info *next; /* Link to next in the list */
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struct linenum_info *prev; /* Line to previous in the list */
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POSITION pos; /* File position */
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POSITION gap; /* Gap between prev and next */
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LINENUM line; /* Line number */
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};
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/*
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* "gap" needs some explanation: the gap of any particular line number
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* is the distance between the previous one and the next one in the list.
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* ("Distance" means difference in file position.) In other words, the
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* gap of a line number is the gap which would be introduced if this
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* line number were deleted. It is used to decide which one to replace
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* when we have a new one to insert and the table is full.
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*/
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#define NPOOL 50 /* Size of line number pool */
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#define LONGTIME (2) /* In seconds */
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public int lnloop = 0; /* Are we in the line num loop? */
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static struct linenum_info anchor; /* Anchor of the list */
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static struct linenum_info *freelist; /* Anchor of the unused entries */
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static struct linenum_info pool[NPOOL]; /* The pool itself */
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static struct linenum_info *spare; /* We always keep one spare entry */
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extern int linenums;
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extern int sigs;
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extern int sc_height;
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/*
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* Initialize the line number structures.
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*/
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public void
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clr_linenum()
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{
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register struct linenum_info *p;
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/*
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* Put all the entries on the free list.
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* Leave one for the "spare".
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*/
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for (p = pool; p < &pool[NPOOL-2]; p++)
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p->next = p+1;
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pool[NPOOL-2].next = NULL;
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freelist = pool;
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spare = &pool[NPOOL-1];
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/*
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* Initialize the anchor.
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*/
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anchor.next = anchor.prev = &anchor;
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anchor.gap = 0;
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anchor.pos = (POSITION)0;
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anchor.line = 1;
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}
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/*
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* Calculate the gap for an entry.
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*/
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static void
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calcgap(p)
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register struct linenum_info *p;
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{
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/*
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* Don't bother to compute a gap for the anchor.
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* Also don't compute a gap for the last one in the list.
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* The gap for that last one should be considered infinite,
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* but we never look at it anyway.
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*/
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if (p == &anchor || p->next == &anchor)
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return;
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p->gap = p->next->pos - p->prev->pos;
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}
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/*
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* Add a new line number to the cache.
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* The specified position (pos) should be the file position of the
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* FIRST character in the specified line.
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*/
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public void
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add_lnum(linenum, pos)
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LINENUM linenum;
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POSITION pos;
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{
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register struct linenum_info *p;
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register struct linenum_info *new;
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register struct linenum_info *nextp;
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register struct linenum_info *prevp;
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register POSITION mingap;
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/*
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* Find the proper place in the list for the new one.
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* The entries are sorted by position.
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*/
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for (p = anchor.next; p != &anchor && p->pos < pos; p = p->next)
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if (p->line == linenum)
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/* We already have this one. */
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return;
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nextp = p;
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prevp = p->prev;
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if (freelist != NULL)
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{
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/*
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* We still have free (unused) entries.
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* Use one of them.
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*/
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new = freelist;
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freelist = freelist->next;
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} else
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{
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/*
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* No free entries.
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* Use the "spare" entry.
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*/
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new = spare;
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spare = NULL;
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}
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/*
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* Fill in the fields of the new entry,
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* and insert it into the proper place in the list.
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*/
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new->next = nextp;
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new->prev = prevp;
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new->pos = pos;
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new->line = linenum;
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nextp->prev = new;
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prevp->next = new;
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/*
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* Recalculate gaps for the new entry and the neighboring entries.
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*/
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calcgap(new);
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calcgap(nextp);
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calcgap(prevp);
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if (spare == NULL)
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{
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/*
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* We have used the spare entry.
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* Scan the list to find the one with the smallest
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* gap, take it out and make it the spare.
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* We should never remove the last one, so stop when
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* we get to p->next == &anchor. This also avoids
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* looking at the gap of the last one, which is
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* not computed by calcgap.
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*/
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mingap = anchor.next->gap;
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for (p = anchor.next; p->next != &anchor; p = p->next)
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{
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if (p->gap <= mingap)
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{
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spare = p;
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mingap = p->gap;
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}
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}
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spare->next->prev = spare->prev;
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spare->prev->next = spare->next;
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}
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}
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/*
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* If we get stuck in a long loop trying to figure out the
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* line number, print a message to tell the user what we're doing.
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*/
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static void
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longloopmessage()
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{
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ierror("Calculating line numbers", NULL_PARG);
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/*
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* Set the lnloop flag here, so if the user interrupts while
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* we are calculating line numbers, the signal handler will
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* turn off line numbers (linenums=0).
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*/
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lnloop = 1;
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}
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static int loopcount;
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#if HAVE_TIME
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static long startime;
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#endif
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static void
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longish()
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{
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#if HAVE_TIME
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if (loopcount >= 0 && ++loopcount > 100)
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{
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loopcount = 0;
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if (get_time() >= startime + LONGTIME)
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{
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longloopmessage();
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loopcount = -1;
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}
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}
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#else
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if (loopcount >= 0 && ++loopcount > LONGLOOP)
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{
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longloopmessage();
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loopcount = -1;
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}
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#endif
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}
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/*
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* Find the line number associated with a given position.
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* Return 0 if we can't figure it out.
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*/
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public LINENUM
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find_linenum(pos)
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POSITION pos;
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{
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register struct linenum_info *p;
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register LINENUM linenum;
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POSITION cpos;
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if (!linenums)
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/*
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* We're not using line numbers.
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*/
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return (0);
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if (pos == NULL_POSITION)
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/*
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* Caller doesn't know what he's talking about.
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*/
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return (0);
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if (pos <= ch_zero())
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/*
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* Beginning of file is always line number 1.
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*/
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return (1);
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/*
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* Find the entry nearest to the position we want.
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*/
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for (p = anchor.next; p != &anchor && p->pos < pos; p = p->next)
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continue;
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if (p->pos == pos)
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/* Found it exactly. */
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return (p->line);
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/*
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* This is the (possibly) time-consuming part.
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* We start at the line we just found and start
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* reading the file forward or backward till we
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* get to the place we want.
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*
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* First decide whether we should go forward from the
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* previous one or backwards from the next one.
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* The decision is based on which way involves
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* traversing fewer bytes in the file.
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*/
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#if HAVE_TIME
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startime = get_time();
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#endif
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if (p == &anchor || pos - p->prev->pos < p->pos - pos)
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{
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/*
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* Go forward.
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*/
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p = p->prev;
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if (ch_seek(p->pos))
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return (0);
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loopcount = 0;
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for (linenum = p->line, cpos = p->pos; cpos < pos; linenum++)
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{
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/*
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* Allow a signal to abort this loop.
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*/
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cpos = forw_raw_line(cpos, (char **)NULL);
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if (ABORT_SIGS() || cpos == NULL_POSITION)
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return (0);
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longish();
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}
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lnloop = 0;
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/*
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* We might as well cache it.
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*/
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add_lnum(linenum, cpos);
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/*
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* If the given position is not at the start of a line,
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* make sure we return the correct line number.
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*/
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if (cpos > pos)
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linenum--;
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} else
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{
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/*
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* Go backward.
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*/
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if (ch_seek(p->pos))
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return (0);
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loopcount = 0;
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for (linenum = p->line, cpos = p->pos; cpos > pos; linenum--)
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{
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/*
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* Allow a signal to abort this loop.
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*/
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cpos = back_raw_line(cpos, (char **)NULL);
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if (ABORT_SIGS() || cpos == NULL_POSITION)
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return (0);
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longish();
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}
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lnloop = 0;
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/*
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* We might as well cache it.
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*/
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add_lnum(linenum, cpos);
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}
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return (linenum);
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}
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/*
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* Find the position of a given line number.
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* Return NULL_POSITION if we can't figure it out.
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*/
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public POSITION
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find_pos(linenum)
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LINENUM linenum;
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{
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register struct linenum_info *p;
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POSITION cpos;
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LINENUM clinenum;
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if (linenum <= 1)
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/*
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* Line number 1 is beginning of file.
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*/
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return (ch_zero());
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/*
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* Find the entry nearest to the line number we want.
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*/
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for (p = anchor.next; p != &anchor && p->line < linenum; p = p->next)
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continue;
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if (p->line == linenum)
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/* Found it exactly. */
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return (p->pos);
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if (p == &anchor || linenum - p->prev->line < p->line - linenum)
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{
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/*
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* Go forward.
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*/
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p = p->prev;
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if (ch_seek(p->pos))
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return (NULL_POSITION);
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for (clinenum = p->line, cpos = p->pos; clinenum < linenum; clinenum++)
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{
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/*
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* Allow a signal to abort this loop.
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*/
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cpos = forw_raw_line(cpos, (char **)NULL);
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if (ABORT_SIGS() || cpos == NULL_POSITION)
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return (NULL_POSITION);
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}
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} else
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{
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/*
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* Go backward.
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*/
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if (ch_seek(p->pos))
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return (NULL_POSITION);
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for (clinenum = p->line, cpos = p->pos; clinenum > linenum; clinenum--)
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{
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/*
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* Allow a signal to abort this loop.
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*/
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cpos = back_raw_line(cpos, (char **)NULL);
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if (ABORT_SIGS() || cpos == NULL_POSITION)
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return (NULL_POSITION);
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}
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}
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/*
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* We might as well cache it.
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*/
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add_lnum(clinenum, cpos);
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return (cpos);
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}
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/*
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* Return the line number of the "current" line.
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* The argument "where" tells which line is to be considered
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* the "current" line (e.g. TOP, BOTTOM, MIDDLE, etc).
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*/
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public LINENUM
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currline(where)
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int where;
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{
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POSITION pos;
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POSITION len;
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LINENUM linenum;
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pos = position(where);
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len = ch_length();
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while (pos == NULL_POSITION && where >= 0 && where < sc_height)
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pos = position(++where);
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if (pos == NULL_POSITION)
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pos = len;
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linenum = find_linenum(pos);
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if (pos == len)
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linenum--;
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return (linenum);
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}
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