Logo Search packages:      
Sourcecode: jless version File versions  Download package

linenum.c

/*
 * Copyright (C) 1984-2000  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 about less, or for information on how to 
 * contact the author, 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
{
      struct linenum *next;         /* Link to next in the list */
      struct linenum *prev;         /* Line to previous in the list */
      POSITION pos;                 /* File position */
      POSITION 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 */

public 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 */

extern int linenums;
extern int sigs;
extern int sc_height;

/*
 * Initialize the line number structures.
 */
      public void
clr_linenum()
{
      register 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 = (POSITION)0;
      anchor.line = 1;
}

/*
 * Calculate the gap for an entry.
 */
      static void
calcgap(p)
      register 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.
 */
      public void
add_lnum(lno, pos)
      int lno;
      POSITION pos;
{
      register struct linenum *p;
      register struct linenum *new;
      register struct linenum *nextp;
      register struct linenum *prevp;
      register 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 == lno)
                  /* 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 = lno;

      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", NULL_PARG);
      /*
       * 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;
}

static int loopcount;
#if HAVE_TIME
static long startime;
#endif

      static void
longish()
{
#if HAVE_TIME
      if (loopcount >= 0 && ++loopcount > 100)
      {
            loopcount = 0;
            if (get_time() >= startime + LONGTIME)
            {
                  longloopmessage();
                  loopcount = -1;
            }
      }
#else
      if (loopcount >= 0 && ++loopcount > LONGLOOP)
      {
            longloopmessage();
            loopcount = -1;
      }
#endif
}

/*
 * Find the line number associated with a given position.
 * Return 0 if we can't figure it out.
 */
      public int
find_linenum(pos)
      POSITION pos;
{
      register struct linenum *p;
      register int lno;
      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.
       */
      flush();
#if HAVE_TIME
      startime = get_time();
#endif
      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, (char **)NULL);
                  if (ABORT_SIGS() || cpos == NULL_POSITION)
                        return (0);
                  longish();
            }
            lnloop = 0;
            /*
             * We might as well cache it.
             */
            add_lnum(lno, cpos);
            /*
             * 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, (char **)NULL);
                  if (ABORT_SIGS() || cpos == NULL_POSITION)
                        return (0);
                  longish();
            }
            lnloop = 0;
            /*
             * We might as well cache it.
             */
            add_lnum(lno, cpos);
      }

      return (lno);
}

/*
 * Find the position of a given line number.
 * Return NULL_POSITION if we can't figure it out.
 */
      public POSITION
find_pos(lno)
      int lno;
{
      register struct linenum *p;
      POSITION cpos;
      int clno;

      if (lno <= 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 < lno;  p = p->next)
            continue;
      if (p->line == lno)
            /* Found it exactly. */
            return (p->pos);

      flush();
      if (p == &anchor || lno - p->prev->line < p->line - lno)
      {
            /*
             * Go forward.
             */
            p = p->prev;
            if (ch_seek(p->pos))
                  return (NULL_POSITION);
            for (clno = p->line, cpos = p->pos;  clno < lno;  clno++)
            {
                  /*
                   * Allow a signal to abort this loop.
                   */
                  cpos = forw_raw_line(cpos, (char **)NULL);
                  if (ABORT_SIGS() || cpos == NULL_POSITION)
                        return (NULL_POSITION);
            }
      } else
      {
            /*
             * Go backward.
             */
            if (ch_seek(p->pos))
                  return (NULL_POSITION);
            for (clno = p->line, cpos = p->pos;  clno > lno;  clno--)
            {
                  /*
                   * Allow a signal to abort this loop.
                   */
                  cpos = back_raw_line(cpos, (char **)NULL);
                  if (ABORT_SIGS() || cpos == NULL_POSITION)
                        return (NULL_POSITION);
            }
      }
      /*
       * We might as well cache it.
       */
      add_lnum(clno, 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 int
currline(where)
      int where;
{
      POSITION pos;
      POSITION len;
      int lnum;

      pos = position(where);
      len = ch_length();
      while (pos == NULL_POSITION && where >= 0 && where < sc_height)
            pos = position(++where);
      if (pos == NULL_POSITION)
            pos = len;
      lnum = find_linenum(pos);
      if (pos == len)
            lnum--;
      return (lnum);
}

Generated by  Doxygen 1.6.0   Back to index