intervals.c 72.3 KB
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/* Code for doing intervals.
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   Copyright (C) 1993, 1994, 1995, 1997, 1998, 2001, 2002, 2003, 2004,
                 2005, 2006, 2007  Free Software Foundation, Inc.
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This file is part of GNU Emacs.

GNU Emacs is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2, or (at your option)
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any later version.

GNU Emacs is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with GNU Emacs; see the file COPYING.  If not, write to
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the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
Boston, MA 02110-1301, USA.  */
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/* NOTES:

   Have to ensure that we can't put symbol nil on a plist, or some
   functions may work incorrectly.

   An idea:  Have the owner of the tree keep count of splits and/or
   insertion lengths (in intervals), and balance after every N.

   Need to call *_left_hook when buffer is killed.

   Scan for zero-length, or 0-length to see notes about handling
   zero length interval-markers.

   There are comments around about freeing intervals.  It might be
   faster to explicitly free them (put them on the free list) than
   to GC them.

*/


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#include <config.h>
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#include "lisp.h"
#include "intervals.h"
#include "buffer.h"
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#include "puresize.h"
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#include "keyboard.h"
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#include "keymap.h"
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/* Test for membership, allowing for t (actually any non-cons) to mean the
   universal set.  */

#define TMEM(sym, set) (CONSP (set) ? ! NILP (Fmemq (sym, set)) : ! NILP (set))

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Lisp_Object merge_properties_sticky ();
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static INTERVAL reproduce_tree P_ ((INTERVAL, INTERVAL));
static INTERVAL reproduce_tree_obj P_ ((INTERVAL, Lisp_Object));
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/* Utility functions for intervals.  */
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/* Create the root interval of some object, a buffer or string.  */
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INTERVAL
create_root_interval (parent)
     Lisp_Object parent;
{
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  INTERVAL new;

  CHECK_IMPURE (parent);

  new = make_interval ();
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  if (BUFFERP (parent))
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    {
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      new->total_length = (BUF_Z (XBUFFER (parent))
			   - BUF_BEG (XBUFFER (parent)));
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      CHECK_TOTAL_LENGTH (new);
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      BUF_INTERVALS (XBUFFER (parent)) = new;
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      new->position = BEG;
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    }
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  else if (STRINGP (parent))
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    {
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      new->total_length = SCHARS (parent);
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      CHECK_TOTAL_LENGTH (new);
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      STRING_SET_INTERVALS (parent, new);
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      new->position = 0;
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    }

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  SET_INTERVAL_OBJECT (new, parent);
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  return new;
}

/* Make the interval TARGET have exactly the properties of SOURCE */

void
copy_properties (source, target)
     register INTERVAL source, target;
{
  if (DEFAULT_INTERVAL_P (source) && DEFAULT_INTERVAL_P (target))
    return;

  COPY_INTERVAL_CACHE (source, target);
  target->plist = Fcopy_sequence (source->plist);
}

/* Merge the properties of interval SOURCE into the properties
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   of interval TARGET.  That is to say, each property in SOURCE
   is added to TARGET if TARGET has no such property as yet.  */
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static void
merge_properties (source, target)
     register INTERVAL source, target;
{
  register Lisp_Object o, sym, val;

  if (DEFAULT_INTERVAL_P (source) && DEFAULT_INTERVAL_P (target))
    return;

  MERGE_INTERVAL_CACHE (source, target);

  o = source->plist;
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  while (CONSP (o))
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    {
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      sym = XCAR (o);
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      val = Fplist_member (target->plist, sym);
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      if (NILP (val))
	{
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	  o = XCDR (o);
	  CHECK_CONS (o);
	  val = XCAR (o);
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	  target->plist = Fcons (sym, Fcons (val, target->plist));
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	  o = XCDR (o);
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	}
      else
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	o = Fcdr (XCDR (o));
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    }
}

/* Return 1 if the two intervals have the same properties,
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   0 otherwise.  */
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int
intervals_equal (i0, i1)
     INTERVAL i0, i1;
{
  register Lisp_Object i0_cdr, i0_sym, i1_val;
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  register int i1_len;
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  if (DEFAULT_INTERVAL_P (i0) && DEFAULT_INTERVAL_P (i1))
    return 1;

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  if (DEFAULT_INTERVAL_P (i0) || DEFAULT_INTERVAL_P (i1))
    return 0;

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  i1_len = XFASTINT (Flength (i1->plist));
  if (i1_len & 0x1)		/* Paranoia -- plists are always even */
    abort ();
  i1_len /= 2;
  i0_cdr = i0->plist;
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  while (CONSP (i0_cdr))
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    {
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      /* Lengths of the two plists were unequal.  */
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      if (i1_len == 0)
	return 0;

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      i0_sym = XCAR (i0_cdr);
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      i1_val = Fplist_member (i1->plist, i0_sym);
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      /* i0 has something i1 doesn't.  */
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      if (EQ (i1_val, Qnil))
	return 0;

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      /* i0 and i1 both have sym, but it has different values in each.  */
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      i0_cdr = XCDR (i0_cdr);
      CHECK_CONS (i0_cdr);
      if (!EQ (Fcar (Fcdr (i1_val)), XCAR (i0_cdr)))
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	return 0;

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      i0_cdr = XCDR (i0_cdr);
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      i1_len--;
    }

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  /* Lengths of the two plists were unequal.  */
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  if (i1_len > 0)
    return 0;

  return 1;
}


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/* Traverse an interval tree TREE, performing FUNCTION on each node.
   No guarantee is made about the order of traversal.
   Pass FUNCTION two args: an interval, and ARG.  */

void
traverse_intervals_noorder (tree, function, arg)
     INTERVAL tree;
     void (* function) P_ ((INTERVAL, Lisp_Object));
     Lisp_Object arg;
{
  /* Minimize stack usage.  */
  while (!NULL_INTERVAL_P (tree))
    {
      (*function) (tree, arg);
      if (NULL_INTERVAL_P (tree->right))
	tree = tree->left;
      else
	{
	  traverse_intervals_noorder (tree->left, function, arg);
	  tree = tree->right;
	}
    }
}

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/* Traverse an interval tree TREE, performing FUNCTION on each node.
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   Pass FUNCTION two args: an interval, and ARG.  */
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void
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traverse_intervals (tree, position, function, arg)
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     INTERVAL tree;
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     int position;
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     void (* function) P_ ((INTERVAL, Lisp_Object));
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     Lisp_Object arg;
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{
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  while (!NULL_INTERVAL_P (tree))
    {
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      traverse_intervals (tree->left, position, function, arg);
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      position += LEFT_TOTAL_LENGTH (tree);
      tree->position = position;
      (*function) (tree, arg);
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      position += LENGTH (tree); tree = tree->right;
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    }
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}

#if 0
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static int icount;
static int idepth;
static int zero_length;

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/* These functions are temporary, for debugging purposes only.  */
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INTERVAL search_interval, found_interval;

void
check_for_interval (i)
     register INTERVAL i;
{
  if (i == search_interval)
    {
      found_interval = i;
      icount++;
    }
}

INTERVAL
search_for_interval (i, tree)
     register INTERVAL i, tree;
{
  icount = 0;
  search_interval = i;
  found_interval = NULL_INTERVAL;
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  traverse_intervals_noorder (tree, &check_for_interval, Qnil);
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  return found_interval;
}

static void
inc_interval_count (i)
     INTERVAL i;
{
  icount++;
  if (LENGTH (i) == 0)
    zero_length++;
  if (depth > idepth)
    idepth = depth;
}

int
count_intervals (i)
     register INTERVAL i;
{
  icount = 0;
  idepth = 0;
  zero_length = 0;
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  traverse_intervals_noorder (i, &inc_interval_count, Qnil);
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  return icount;
}

static INTERVAL
root_interval (interval)
     INTERVAL interval;
{
  register INTERVAL i = interval;

  while (! ROOT_INTERVAL_P (i))
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    i = INTERVAL_PARENT (i);
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  return i;
}
#endif

/* Assuming that a left child exists, perform the following operation:

     A		  B
    / \		 / \
   B       =>       A
  / \		   / \
     c		  c
*/

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static INLINE INTERVAL
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rotate_right (interval)
     INTERVAL interval;
{
  INTERVAL i;
  INTERVAL B = interval->left;
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  int old_total = interval->total_length;
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  /* Deal with any Parent of A;  make it point to B.  */
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  if (! ROOT_INTERVAL_P (interval))
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    {
      if (AM_LEFT_CHILD (interval))
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	INTERVAL_PARENT (interval)->left = B;
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      else
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	INTERVAL_PARENT (interval)->right = B;
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    }
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  COPY_INTERVAL_PARENT (B, interval);
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  /* Make B the parent of A */
  i = B->right;
  B->right = interval;
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  SET_INTERVAL_PARENT (interval, B);
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  /* Make A point to c */
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  interval->left = i;
  if (! NULL_INTERVAL_P (i))
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    SET_INTERVAL_PARENT (i, interval);
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  /* A's total length is decreased by the length of B and its left child.  */
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  interval->total_length -= B->total_length - LEFT_TOTAL_LENGTH (interval);
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  CHECK_TOTAL_LENGTH (interval);
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  /* B must have the same total length of A.  */
  B->total_length = old_total;
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  CHECK_TOTAL_LENGTH (B);
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  return B;
}
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/* Assuming that a right child exists, perform the following operation:

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    A               B
   / \	           / \
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      B	   =>     A
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     / \         / \
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    c               c
*/

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static INLINE INTERVAL
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rotate_left (interval)
     INTERVAL interval;
{
  INTERVAL i;
  INTERVAL B = interval->right;
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  int old_total = interval->total_length;
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  /* Deal with any parent of A;  make it point to B.  */
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  if (! ROOT_INTERVAL_P (interval))
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    {
      if (AM_LEFT_CHILD (interval))
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	INTERVAL_PARENT (interval)->left = B;
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      else
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	INTERVAL_PARENT (interval)->right = B;
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    }
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  COPY_INTERVAL_PARENT (B, interval);
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  /* Make B the parent of A */
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  i = B->left;
  B->left = interval;
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  SET_INTERVAL_PARENT (interval, B);
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  /* Make A point to c */
  interval->right = i;
  if (! NULL_INTERVAL_P (i))
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    SET_INTERVAL_PARENT (i, interval);
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  /* A's total length is decreased by the length of B and its right child.  */
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  interval->total_length -= B->total_length - RIGHT_TOTAL_LENGTH (interval);
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  CHECK_TOTAL_LENGTH (interval);
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  /* B must have the same total length of A.  */
  B->total_length = old_total;
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  CHECK_TOTAL_LENGTH (B);
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  return B;
}

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/* Balance an interval tree with the assumption that the subtrees
   themselves are already balanced.  */

static INTERVAL
balance_an_interval (i)
     INTERVAL i;
{
  register int old_diff, new_diff;

  while (1)
    {
      old_diff = LEFT_TOTAL_LENGTH (i) - RIGHT_TOTAL_LENGTH (i);
      if (old_diff > 0)
	{
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	  /* Since the left child is longer, there must be one.  */
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	  new_diff = i->total_length - i->left->total_length
	    + RIGHT_TOTAL_LENGTH (i->left) - LEFT_TOTAL_LENGTH (i->left);
	  if (abs (new_diff) >= old_diff)
	    break;
	  i = rotate_right (i);
	  balance_an_interval (i->right);
	}
      else if (old_diff < 0)
	{
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	  /* Since the right child is longer, there must be one.  */
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	  new_diff = i->total_length - i->right->total_length
	    + LEFT_TOTAL_LENGTH (i->right) - RIGHT_TOTAL_LENGTH (i->right);
	  if (abs (new_diff) >= -old_diff)
	    break;
	  i = rotate_left (i);
	  balance_an_interval (i->left);
	}
      else
	break;
    }
  return i;
}

/* Balance INTERVAL, potentially stuffing it back into its parent
   Lisp Object.  */

static INLINE INTERVAL
balance_possible_root_interval (interval)
     register INTERVAL interval;
{
  Lisp_Object parent;
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  int have_parent = 0;
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  if (!INTERVAL_HAS_OBJECT (interval) && !INTERVAL_HAS_PARENT (interval))
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    return interval;

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  if (INTERVAL_HAS_OBJECT (interval))
    {
      have_parent = 1;
      GET_INTERVAL_OBJECT (parent, interval);
    }
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  interval = balance_an_interval (interval);

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  if (have_parent)
    {
      if (BUFFERP (parent))
	BUF_INTERVALS (XBUFFER (parent)) = interval;
      else if (STRINGP (parent))
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	STRING_SET_INTERVALS (parent, interval);
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    }
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  return interval;
}

/* Balance the interval tree TREE.  Balancing is by weight
   (the amount of text).  */

static INTERVAL
balance_intervals_internal (tree)
     register INTERVAL tree;
{
  /* Balance within each side.  */
  if (tree->left)
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    balance_intervals_internal (tree->left);
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  if (tree->right)
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    balance_intervals_internal (tree->right);
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  return balance_an_interval (tree);
}

/* Advertised interface to balance intervals.  */

INTERVAL
balance_intervals (tree)
     INTERVAL tree;
{
  if (tree == NULL_INTERVAL)
    return NULL_INTERVAL;

  return balance_intervals_internal (tree);
}

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/* Split INTERVAL into two pieces, starting the second piece at
   character position OFFSET (counting from 0), relative to INTERVAL.
   INTERVAL becomes the left-hand piece, and the right-hand piece
   (second, lexicographically) is returned.
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   The size and position fields of the two intervals are set based upon
   those of the original interval.  The property list of the new interval
   is reset, thus it is up to the caller to do the right thing with the
   result.
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   Note that this does not change the position of INTERVAL;  if it is a root,
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   it is still a root after this operation.  */
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INTERVAL
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split_interval_right (interval, offset)
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     INTERVAL interval;
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     int offset;
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{
  INTERVAL new = make_interval ();
  int position = interval->position;
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  int new_length = LENGTH (interval) - offset;
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  new->position = position + offset;
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  SET_INTERVAL_PARENT (new, interval);
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  if (NULL_RIGHT_CHILD (interval))
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    {
      interval->right = new;
      new->total_length = new_length;
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      CHECK_TOTAL_LENGTH (new);
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    }
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  else
    {
      /* Insert the new node between INTERVAL and its right child.  */
      new->right = interval->right;
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      SET_INTERVAL_PARENT (interval->right, new);
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      interval->right = new;
      new->total_length = new_length + new->right->total_length;
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      CHECK_TOTAL_LENGTH (new);
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      balance_an_interval (new);
    }
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  balance_possible_root_interval (interval);

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  return new;
}

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/* Split INTERVAL into two pieces, starting the second piece at
   character position OFFSET (counting from 0), relative to INTERVAL.
   INTERVAL becomes the right-hand piece, and the left-hand piece
   (first, lexicographically) is returned.
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   The size and position fields of the two intervals are set based upon
   those of the original interval.  The property list of the new interval
   is reset, thus it is up to the caller to do the right thing with the
   result.

   Note that this does not change the position of INTERVAL;  if it is a root,
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   it is still a root after this operation.  */
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INTERVAL
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split_interval_left (interval, offset)
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     INTERVAL interval;
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     int offset;
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{
  INTERVAL new = make_interval ();
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  int new_length = offset;
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  new->position = interval->position;
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  interval->position = interval->position + offset;
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  SET_INTERVAL_PARENT (new, interval);
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  if (NULL_LEFT_CHILD (interval))
    {
      interval->left = new;
      new->total_length = new_length;
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      CHECK_TOTAL_LENGTH (new);
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    }
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  else
    {
      /* Insert the new node between INTERVAL and its left child.  */
      new->left = interval->left;
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      SET_INTERVAL_PARENT (new->left, new);
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      interval->left = new;
      new->total_length = new_length + new->left->total_length;
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      CHECK_TOTAL_LENGTH (new);
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      balance_an_interval (new);
    }
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  balance_possible_root_interval (interval);
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  return new;
}

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/* Return the proper position for the first character
   described by the interval tree SOURCE.
   This is 1 if the parent is a buffer,
   0 if the parent is a string or if there is no parent.

   Don't use this function on an interval which is the child
   of another interval!  */

int
interval_start_pos (source)
     INTERVAL source;
{
  Lisp_Object parent;

  if (NULL_INTERVAL_P (source))
    return 0;

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  if (! INTERVAL_HAS_OBJECT (source))
    return 0;
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  GET_INTERVAL_OBJECT (parent, source);
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  if (BUFFERP (parent))
    return BUF_BEG (XBUFFER (parent));
  return 0;
}

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/* Find the interval containing text position POSITION in the text
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   represented by the interval tree TREE.  POSITION is a buffer
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   position (starting from 1) or a string index (starting from 0).
   If POSITION is at the end of the buffer or string,
   return the interval containing the last character.
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   The `position' field, which is a cache of an interval's position,
   is updated in the interval found.  Other functions (e.g., next_interval)
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   will update this cache based on the result of find_interval.  */
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INTERVAL
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find_interval (tree, position)
     register INTERVAL tree;
     register int position;
{
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  /* The distance from the left edge of the subtree at TREE
                    to POSITION.  */
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  register int relative_position;
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  if (NULL_INTERVAL_P (tree))
    return NULL_INTERVAL;

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  relative_position = position;
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  if (INTERVAL_HAS_OBJECT (tree))
    {
      Lisp_Object parent;
      GET_INTERVAL_OBJECT (parent, tree);
      if (BUFFERP (parent))
	relative_position -= BUF_BEG (XBUFFER (parent));
    }
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  if (relative_position > TOTAL_LENGTH (tree))
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    abort ();			/* Paranoia */

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  if (!handling_signal)
    tree = balance_possible_root_interval (tree);
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  while (1)
    {
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      if (relative_position < LEFT_TOTAL_LENGTH (tree))
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	{
	  tree = tree->left;
	}
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      else if (! NULL_RIGHT_CHILD (tree)
	       && relative_position >= (TOTAL_LENGTH (tree)
					- RIGHT_TOTAL_LENGTH (tree)))
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	{
	  relative_position -= (TOTAL_LENGTH (tree)
				- RIGHT_TOTAL_LENGTH (tree));
	  tree = tree->right;
	}
      else
	{
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	  tree->position
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	    = (position - relative_position /* left edge of *tree.  */
	       + LEFT_TOTAL_LENGTH (tree)); /* left edge of this interval.  */
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	  return tree;
	}
    }
}

/* Find the succeeding interval (lexicographically) to INTERVAL.
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   Sets the `position' field based on that of INTERVAL (see
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   find_interval).  */
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INTERVAL
next_interval (interval)
     register INTERVAL interval;
{
  register INTERVAL i = interval;
  register int next_position;

  if (NULL_INTERVAL_P (i))
    return NULL_INTERVAL;
  next_position = interval->position + LENGTH (interval);

  if (! NULL_RIGHT_CHILD (i))
    {
      i = i->right;
      while (! NULL_LEFT_CHILD (i))
	i = i->left;

      i->position = next_position;
      return i;
    }

  while (! NULL_PARENT (i))
    {
      if (AM_LEFT_CHILD (i))
	{
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	  i = INTERVAL_PARENT (i);
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	  i->position = next_position;
	  return i;
	}

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      i = INTERVAL_PARENT (i);
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    }

  return NULL_INTERVAL;
}

/* Find the preceding interval (lexicographically) to INTERVAL.
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   Sets the `position' field based on that of INTERVAL (see
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   find_interval).  */
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INTERVAL
previous_interval (interval)
     register INTERVAL interval;
{
  register INTERVAL i;

  if (NULL_INTERVAL_P (interval))
    return NULL_INTERVAL;

  if (! NULL_LEFT_CHILD (interval))
    {
      i = interval->left;
      while (! NULL_RIGHT_CHILD (i))
	i = i->right;

      i->position = interval->position - LENGTH (i);
      return i;
    }

  i = interval;
  while (! NULL_PARENT (i))
    {
      if (AM_RIGHT_CHILD (i))
	{
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	  i = INTERVAL_PARENT (i);
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	  i->position = interval->position - LENGTH (i);
	  return i;
	}
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      i = INTERVAL_PARENT (i);
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    }

  return NULL_INTERVAL;
}
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/* Find the interval containing POS given some non-NULL INTERVAL
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   in the same tree.  Note that we need to update interval->position
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   if we go down the tree.
   To speed up the process, we assume that the ->position of
   I and all its parents is already uptodate.  */
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INTERVAL
update_interval (i, pos)
     register INTERVAL i;
     int pos;
{
  if (NULL_INTERVAL_P (i))
    return NULL_INTERVAL;

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  while (1)
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    {
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      if (pos < i->position)
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	{
	  /* Move left. */
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	  if (pos >= i->position - TOTAL_LENGTH (i->left))
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	    {
	      i->left->position = i->position - TOTAL_LENGTH (i->left)
		+ LEFT_TOTAL_LENGTH (i->left);
	      i = i->left;		/* Move to the left child */
	    }
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	  else if (NULL_PARENT (i))
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	    error ("Point before start of properties");
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	  else
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	      i = INTERVAL_PARENT (i);
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	  continue;
	}
      else if (pos >= INTERVAL_LAST_POS (i))
	{
	  /* Move right. */
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	  if (pos < INTERVAL_LAST_POS (i) + TOTAL_LENGTH (i->right))
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	    {
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	      i->right->position = INTERVAL_LAST_POS (i)
	        + LEFT_TOTAL_LENGTH (i->right);
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	      i = i->right;		/* Move to the right child */
	    }
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	  else if (NULL_PARENT (i))
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	    error ("Point %d after end of properties", pos);
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	  else
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            i = INTERVAL_PARENT (i);
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	  continue;
	}
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      else
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	return i;
    }
}

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#if 0
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/* Traverse a path down the interval tree TREE to the interval
   containing POSITION, adjusting all nodes on the path for
   an addition of LENGTH characters.  Insertion between two intervals
   (i.e., point == i->position, where i is second interval) means
   text goes into second interval.

   Modifications are needed to handle the hungry bits -- after simply
   finding the interval at position (don't add length going down),
   if it's the beginning of the interval, get the previous interval
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   and check the hungry bits of both.  Then add the length going back up
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   to the root.  */
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static INTERVAL
adjust_intervals_for_insertion (tree, position, length)
     INTERVAL tree;
     int position, length;
{
  register int relative_position;
  register INTERVAL this;

  if (TOTAL_LENGTH (tree) == 0)	/* Paranoia */
    abort ();

  /* If inserting at point-max of a buffer, that position
     will be out of range */
  if (position > TOTAL_LENGTH (tree))
    position = TOTAL_LENGTH (tree);
  relative_position = position;
  this = tree;

  while (1)
    {
      if (relative_position <= LEFT_TOTAL_LENGTH (this))
	{
	  this->total_length += length;
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	  CHECK_TOTAL_LENGTH (this);
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	  this = this->left;
	}
      else if (relative_position > (TOTAL_LENGTH (this)
				    - RIGHT_TOTAL_LENGTH (this)))
	{
	  relative_position -= (TOTAL_LENGTH (this)
				- RIGHT_TOTAL_LENGTH (this));
	  this->total_length += length;
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	  CHECK_TOTAL_LENGTH (this);
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	  this = this->right;
	}
      else
	{
	  /* If we are to use zero-length intervals as buffer pointers,
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	     then this code will have to change.  */
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	  this->total_length += length;
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	  CHECK_TOTAL_LENGTH (this);
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	  this->position = LEFT_TOTAL_LENGTH (this)
	                   + position - relative_position + 1;
	  return tree;
	}
    }
}
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#endif

/* Effect an adjustment corresponding to the addition of LENGTH characters
   of text.  Do this by finding the interval containing POSITION in the
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   interval tree TREE, and then adjusting all of its ancestors by adding
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   LENGTH to them.

   If POSITION is the first character of an interval, meaning that point
   is actually between the two intervals, make the new text belong to
   the interval which is "sticky".

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   If both intervals are "sticky", then make them belong to the left-most
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   interval.  Another possibility would be to create a new interval for
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   this text, and make it have the merged properties of both ends.  */
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static INTERVAL
adjust_intervals_for_insertion (tree, position, length)
     INTERVAL tree;
     int position, length;
{
  register INTERVAL i;
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  register INTERVAL temp;
  int eobp = 0;
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  Lisp_Object parent;
  int offset;
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  if (TOTAL_LENGTH (tree) == 0)	/* Paranoia */
    abort ();

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  GET_INTERVAL_OBJECT (parent, tree);
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  offset = (BUFFERP (parent) ? BUF_BEG (XBUFFER (parent)) : 0);

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  /* If inserting at point-max of a buffer, that position will be out
     of range.  Remember that buffer positions are 1-based.  */
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  if (position >= TOTAL_LENGTH (tree) + offset)
    {
      position = TOTAL_LENGTH (tree) + offset;
      eobp = 1;
    }
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  i = find_interval (tree, position);
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  /* If in middle of an interval which is not sticky either way,
     we must not just give its properties to the insertion.
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     So split this interval at the insertion point.

     Originally, the if condition here was this:
	(! (position == i->position || eobp)
	 && END_NONSTICKY_P (i)
	 && FRONT_NONSTICKY_P (i))
     But, these macros are now unreliable because of introduction of
     Vtext_property_default_nonsticky.  So, we always check properties
     one by one if POSITION is in middle of an interval.  */
  if (! (position == i->position || eobp))
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    {
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      Lisp_Object tail;
      Lisp_Object front, rear;

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      tail = i->plist;

      /* Properties font-sticky and rear-nonsticky override
         Vtext_property_default_nonsticky.  So, if they are t, we can
         skip one by one checking of properties.  */
      rear = textget (i->plist, Qrear_nonsticky);
      if (! CONSP (rear) && ! NILP (rear))
	{
	  /* All properties are nonsticky.  We split the interval.  */
	  goto check_done;
	}
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      front = textget (i->plist, Qfront_sticky);
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      if (! CONSP (front) && ! NILP (front))
	{
	  /* All properties are sticky.  We don't split the interval.  */
	  tail = Qnil;
	  goto check_done;
	}
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      /* Does any actual property pose an actual problem?  We break
         the loop if we find a nonsticky property.  */
      for (; CONSP (tail); tail = Fcdr (XCDR (tail)))
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	{
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	  Lisp_Object prop, tmp;
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	  prop = XCAR (tail);
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	  /* Is this particular property front-sticky?  */
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	  if (CONSP (front) && ! NILP (Fmemq (prop, front)))
	    continue;

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	  /* Is this particular property rear-nonsticky?  */
	  if (CONSP (rear) && ! NILP (Fmemq (prop, rear)))
	    break;

	  /* Is this particular property recorded as sticky or
             nonsticky in Vtext_property_default_nonsticky?  */
	  tmp = Fassq (prop, Vtext_property_default_nonsticky);
	  if (CONSP (tmp))
	    {
	      if (NILP (tmp))
		continue;
	      break;
	    }

	  /* By default, a text property is rear-sticky, thus we
	     continue the loop.  */
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	}

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    check_done:
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      /* If any property is a real problem, split the interval.  */
      if (! NILP (tail))
	{
	  temp = split_interval_right (i, position - i->position);
	  copy_properties (i, temp);
	  i = temp;
	}
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    }

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  /* If we are positioned between intervals, check the stickiness of
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     both of them.  We have to do this too, if we are at BEG or Z.  */
  if (position == i->position || eobp)
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    {
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      register INTERVAL prev;

      if (position == BEG)
	prev = 0;
      else if (eobp)
	{
	  prev = i;
	  i = 0;
	}
      else
	prev = previous_interval (i);
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      /* Even if we are positioned between intervals, we default
	 to the left one if it exists.  We extend it now and split
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	 off a part later, if stickiness demands it.  */
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      for (temp = prev ? prev : i; temp; temp = INTERVAL_PARENT_OR_NULL (temp))
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	{
	  temp->total_length += length;
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	  CHECK_TOTAL_LENGTH (temp);
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	  temp = balance_possible_root_interval (temp);
	}
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      /* If at least one interval has sticky properties,
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	 we check the stickiness property by property.

	 Originally, the if condition here was this:
		(END_NONSTICKY_P (prev) || FRONT_STICKY_P (i))
	 But, these macros are now unreliable because of introduction
	 of Vtext_property_default_nonsticky.  So, we always have to
	 check stickiness of properties one by one.  If cache of
	 stickiness is implemented in the future, we may be able to
	 use those macros again.  */
      if (1)
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	{
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	  Lisp_Object pleft, pright;
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	  struct interval newi;

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	  pleft = NULL_INTERVAL_P (prev) ? Qnil : prev->plist;
	  pright = NULL_INTERVAL_P (i) ? Qnil : i->plist;
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	  newi.plist = merge_properties_sticky (pleft, pright);

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	  if (! prev) /* i.e. position == BEG */
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	    {
	      if (! intervals_equal (i, &newi))
		{
		  i = split_interval_left (i, length);
		  i->plist = newi.plist;
		}
	    }
	  else if (! intervals_equal (prev, &newi))
	    {
	      prev = split_interval_right (prev,
					   position - prev->position);