* lisp/emacs-lisp/gv.el (gv-define-setter): Silence compiler warning

[emacs.git] / src / intervals.c

/* Code for doing intervals.
   Copyright (C) 1993-1995, 1997-1998, 2001-2018 Free Software
   Foundation, Inc.

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
the Free Software Foundation, either version 3 of the License, or (at
your option) 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.  If not, see <https://www.gnu.org/licenses/>.  */


/* 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.

*/


#include <config.h>

#include <intprops.h>
#include "lisp.h"
#include "intervals.h"
#include "buffer.h"
#include "puresize.h"
#include "keymap.h"

/* 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))

static Lisp_Object merge_properties_sticky (Lisp_Object, Lisp_Object);
static INTERVAL merge_interval_right (INTERVAL);
static INTERVAL reproduce_tree (INTERVAL, INTERVAL);
\f
/* Utility functions for intervals.  */

/* Use these functions to set pointer slots of struct interval.  */

static void
set_interval_left (INTERVAL i, INTERVAL left)
{
  i->left = left;
}

static void
set_interval_right (INTERVAL i, INTERVAL right)
{
  i->right = right;
}

/* Make the parent of D be whatever the parent of S is, regardless
   of the type.  This is used when balancing an interval tree.  */

static void
copy_interval_parent (INTERVAL d, INTERVAL s)
{
  d->up = s->up;
  d->up_obj = s->up_obj;
}

/* Create the root interval of some object, a buffer or string.  */

INTERVAL
create_root_interval (Lisp_Object parent)
{
  INTERVAL new;

  new = make_interval ();

  if (! STRINGP (parent))
    {
      new->total_length = (BUF_Z (XBUFFER (parent))
                           - BUF_BEG (XBUFFER (parent)));
      eassert (TOTAL_LENGTH (new) >= 0);
      set_buffer_intervals (XBUFFER (parent), new);
      new->position = BEG;
    }
  else
    {
      CHECK_IMPURE (parent, XSTRING (parent));
      new->total_length = SCHARS (parent);
      eassert (TOTAL_LENGTH (new) >= 0);
      set_string_intervals (parent, new);
      new->position = 0;
    }
  eassert (LENGTH (new) > 0);

  set_interval_object (new, parent);

  return new;
}

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

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

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

/* Merge the properties of interval SOURCE into the properties
   of interval TARGET.  That is to say, each property in SOURCE
   is added to TARGET if TARGET has no such property as yet.  */

static void
merge_properties (register INTERVAL source, register INTERVAL 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;
  while (CONSP (o))
    {
      sym = XCAR (o);
      o = XCDR (o);
      CHECK_CONS (o);

      val = target->plist;
      while (CONSP (val) && !EQ (XCAR (val), sym))
        {
          val = XCDR (val);
          if (!CONSP (val))
            break;
          val = XCDR (val);
        }

      if (NILP (val))
        {
          val = XCAR (o);
          set_interval_plist (target, Fcons (sym, Fcons (val, target->plist)));
        }
      o = XCDR (o);
    }
}

/* Return true if the two intervals have the same properties.  */

bool
intervals_equal (INTERVAL i0, INTERVAL i1)
{
  Lisp_Object i0_cdr, i0_sym;
  Lisp_Object i1_cdr, i1_val;

  if (DEFAULT_INTERVAL_P (i0) && DEFAULT_INTERVAL_P (i1))
    return true;

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

  i0_cdr = i0->plist;
  i1_cdr = i1->plist;
  while (CONSP (i0_cdr) && CONSP (i1_cdr))
    {
      i0_sym = XCAR (i0_cdr);
      i0_cdr = XCDR (i0_cdr);
      if (!CONSP (i0_cdr))
        return false;
      i1_val = i1->plist;
      while (CONSP (i1_val) && !EQ (XCAR (i1_val), i0_sym))
        {
          i1_val = XCDR (i1_val);
          if (!CONSP (i1_val))
            return false;
          i1_val = XCDR (i1_val);
        }

      /* i0 has something i1 doesn't.  */
      if (EQ (i1_val, Qnil))
        return false;

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

      i0_cdr = XCDR (i0_cdr);

      i1_cdr = XCDR (i1_cdr);
      if (!CONSP (i1_cdr))
        return false;
      i1_cdr = XCDR (i1_cdr);
    }

  /* Lengths of the two plists were equal.  */
  return (NILP (i0_cdr) && NILP (i1_cdr));
}
\f

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

/* Traverse an interval tree TREE, performing FUNCTION on each node.
   Pass FUNCTION two args: an interval, and ARG.  */

void
traverse_intervals (INTERVAL tree, ptrdiff_t position,
                    void (*function) (INTERVAL, Lisp_Object), Lisp_Object arg)
{
  while (tree)
    {
      traverse_intervals (tree->left, position, function, arg);
      position += LEFT_TOTAL_LENGTH (tree);
      tree->position = position;
      (*function) (tree, arg);
      position += LENGTH (tree); tree = tree->right;
    }
}
\f
/* Assuming that a left child exists, perform the following operation:

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

static INTERVAL
rotate_right (INTERVAL A)
{
  INTERVAL B = A->left;
  INTERVAL c = B->right;
  ptrdiff_t old_total = A->total_length;

  eassert (old_total > 0);
  eassert (LENGTH (A) > 0);
  eassert (LENGTH (B) > 0);

  /* Deal with any Parent of A;  make it point to B.  */
  if (! ROOT_INTERVAL_P (A))
    {
      if (AM_LEFT_CHILD (A))
        set_interval_left (INTERVAL_PARENT (A), B);
      else
        set_interval_right (INTERVAL_PARENT (A), B);
    }
  copy_interval_parent (B, A);

  /* Make B the parent of A.  */
  set_interval_right (B, A);
  set_interval_parent (A, B);

  /* Make A point to c.  */
  set_interval_left (A, c);
  if (c)
    set_interval_parent (c, A);

  /* A's total length is decreased by the length of B and its left child.  */
  A->total_length -= B->total_length - TOTAL_LENGTH (c);
  eassert (TOTAL_LENGTH (A) > 0);
  eassert (LENGTH (A) > 0);

  /* B must have the same total length of A.  */
  B->total_length = old_total;
  eassert (LENGTH (B) > 0);

  return B;
}

/* Assuming that a right child exists, perform the following operation:

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

static INTERVAL
rotate_left (INTERVAL A)
{
  INTERVAL B = A->right;
  INTERVAL c = B->left;
  ptrdiff_t old_total = A->total_length;

  eassert (old_total > 0);
  eassert (LENGTH (A) > 0);
  eassert (LENGTH (B) > 0);

  /* Deal with any parent of A;  make it point to B.  */
  if (! ROOT_INTERVAL_P (A))
    {
      if (AM_LEFT_CHILD (A))
        set_interval_left (INTERVAL_PARENT (A), B);
      else
        set_interval_right (INTERVAL_PARENT (A), B);
    }
  copy_interval_parent (B, A);

  /* Make B the parent of A.  */
  set_interval_left (B, A);
  set_interval_parent (A, B);

  /* Make A point to c.  */
  set_interval_right (A, c);
  if (c)
    set_interval_parent (c, A);

  /* A's total length is decreased by the length of B and its right child.  */
  A->total_length -= B->total_length - TOTAL_LENGTH (c);
  eassert (TOTAL_LENGTH (A) > 0);
  eassert (LENGTH (A) > 0);

  /* B must have the same total length of A.  */
  B->total_length = old_total;
  eassert (LENGTH (B) > 0);

  return B;
}
\f
/* Balance an interval tree with the assumption that the subtrees
   themselves are already balanced.  */

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

  eassert (LENGTH (i) > 0);
  eassert (TOTAL_LENGTH (i) >= LENGTH (i));

  while (1)
    {
      old_diff = LEFT_TOTAL_LENGTH (i) - RIGHT_TOTAL_LENGTH (i);
      if (old_diff > 0)
        {
          /* Since the left child is longer, there must be one.  */
          new_diff = i->total_length - i->left->total_length
            + RIGHT_TOTAL_LENGTH (i->left) - LEFT_TOTAL_LENGTH (i->left);
          if (eabs (new_diff) >= old_diff)
            break;
          i = rotate_right (i);
          balance_an_interval (i->right);
        }
      else if (old_diff < 0)
        {
          /* Since the right child is longer, there must be one.  */
          new_diff = i->total_length - i->right->total_length
            + LEFT_TOTAL_LENGTH (i->right) - RIGHT_TOTAL_LENGTH (i->right);
          if (eabs (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 INTERVAL
balance_possible_root_interval (INTERVAL interval)
{
  Lisp_Object parent;
  bool have_parent = false;

  if (INTERVAL_HAS_OBJECT (interval))
    {
      have_parent = true;
      GET_INTERVAL_OBJECT (parent, interval);
    }
  else if (!INTERVAL_HAS_PARENT (interval))
    return interval;

  interval = balance_an_interval (interval);

  if (have_parent)
    {
      if (BUFFERP (parent))
        set_buffer_intervals (XBUFFER (parent), interval);
      else if (STRINGP (parent))
        set_string_intervals (parent, interval);
    }

  return interval;
}

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

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

/* Advertised interface to balance intervals.  */

INTERVAL
balance_intervals (INTERVAL tree)
{
  return tree ? balance_intervals_internal (tree) : NULL;
}

/* Rebalance text properties of B.  */

static void
buffer_balance_intervals (struct buffer *b)
{
  INTERVAL i;

  eassert (b != NULL);
  i = buffer_intervals (b);
  if (i)
    set_buffer_intervals (b, balance_an_interval (i));
}

/* 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.

   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,
   it is still a root after this operation.  */

INTERVAL
split_interval_right (INTERVAL interval, ptrdiff_t offset)
{
  INTERVAL new = make_interval ();
  ptrdiff_t position = interval->position;
  ptrdiff_t new_length = LENGTH (interval) - offset;

  new->position = position + offset;
  set_interval_parent (new, interval);

  if (NULL_RIGHT_CHILD (interval))
    {
      set_interval_right (interval, new);
      new->total_length = new_length;
      eassert (LENGTH (new) > 0);
    }
  else
    {
      /* Insert the new node between INTERVAL and its right child.  */
      set_interval_right (new, interval->right);
      set_interval_parent (interval->right, new);
      set_interval_right (interval, new);
      new->total_length = new_length + new->right->total_length;
      balance_an_interval (new);
    }

  balance_possible_root_interval (interval);

  return new;
}

/* 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.

   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,
   it is still a root after this operation.  */

INTERVAL
split_interval_left (INTERVAL interval, ptrdiff_t offset)
{
  INTERVAL new = make_interval ();
  ptrdiff_t new_length = offset;

  new->position = interval->position;
  interval->position = interval->position + offset;
  set_interval_parent (new, interval);

  if (NULL_LEFT_CHILD (interval))
    {
      set_interval_left (interval, new);
      new->total_length = new_length;
      eassert (LENGTH (new) > 0);
    }
  else
    {
      /* Insert the new node between INTERVAL and its left child.  */
      set_interval_left (new, interval->left);
      set_interval_parent (new->left, new);
      set_interval_left (interval, new);
      new->total_length = new_length + new->left->total_length;
      balance_an_interval (new);
    }

  balance_possible_root_interval (interval);

  return new;
}
\f
/* 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!  */

static int
interval_start_pos (INTERVAL source)
{
  Lisp_Object parent;

  if (!source)
    return 0;

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

/* Find the interval containing text position POSITION in the text
   represented by the interval tree TREE.  POSITION is a buffer
   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.

   The `position' field, which is a cache of an interval's position,
   is updated in the interval found.  Other functions (e.g., next_interval)
   will update this cache based on the result of find_interval.  */

INTERVAL
find_interval (register INTERVAL tree, register ptrdiff_t position)
{
  /* The distance from the left edge of the subtree at TREE
                    to POSITION.  */
  register ptrdiff_t relative_position;

  if (!tree)
    return NULL;

  relative_position = position;
  if (INTERVAL_HAS_OBJECT (tree))
    {
      Lisp_Object parent;
      GET_INTERVAL_OBJECT (parent, tree);
      if (BUFFERP (parent))
        relative_position -= BUF_BEG (XBUFFER (parent));
    }

  eassert (relative_position <= TOTAL_LENGTH (tree));

  tree = balance_possible_root_interval (tree);

  while (1)
    {
      eassert (tree);
      if (relative_position < LEFT_TOTAL_LENGTH (tree))
        {
          tree = tree->left;
        }
      else if (! NULL_RIGHT_CHILD (tree)
               && relative_position >= (TOTAL_LENGTH (tree)
                                        - RIGHT_TOTAL_LENGTH (tree)))
        {
          relative_position -= (TOTAL_LENGTH (tree)
                                - RIGHT_TOTAL_LENGTH (tree));
          tree = tree->right;
        }
      else
        {
          tree->position
            = (position - relative_position /* left edge of *tree.  */
               + LEFT_TOTAL_LENGTH (tree)); /* left edge of this interval.  */

          return tree;
        }
    }
}
\f
/* Find the succeeding interval (lexicographically) to INTERVAL.
   Sets the `position' field based on that of INTERVAL (see
   find_interval).  */

INTERVAL
next_interval (register INTERVAL interval)
{
  register INTERVAL i = interval;
  register ptrdiff_t next_position;

  if (!i)
    return NULL;
  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))
        {
          i = INTERVAL_PARENT (i);
          i->position = next_position;
          return i;
        }

      i = INTERVAL_PARENT (i);
    }

  return NULL;
}

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

INTERVAL
previous_interval (register INTERVAL interval)
{
  register INTERVAL i;

  if (!interval)
    return NULL;

  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))
        {
          i = INTERVAL_PARENT (i);

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

  return NULL;
}

/* Find the interval containing POS given some non-NULL INTERVAL
   in the same tree.  Note that we need to update interval->position
   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.  */
INTERVAL
update_interval (register INTERVAL i, ptrdiff_t pos)
{
  if (!i)
    return NULL;

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

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

   If both intervals are "sticky", then make them belong to the left-most
   interval.  Another possibility would be to create a new interval for
   this text, and make it have the merged properties of both ends.  */

static INTERVAL
adjust_intervals_for_insertion (INTERVAL tree,
                                ptrdiff_t position, ptrdiff_t length)
{
  INTERVAL i;
  INTERVAL temp;
  bool eobp = 0;
  Lisp_Object parent;
  ptrdiff_t offset;

  eassert (TOTAL_LENGTH (tree) > 0);

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

  /* If inserting at point-max of a buffer, that position will be out
     of range.  Remember that buffer positions are 1-based.  */
  if (position >= TOTAL_LENGTH (tree) + offset)
    {
      position = TOTAL_LENGTH (tree) + offset;
      eobp = 1;
    }

  i = find_interval (tree, position);

  /* If in middle of an interval which is not sticky either way,
     we must not just give its properties to the insertion.
     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))
    {
      Lisp_Object tail;
      Lisp_Object front, rear;

      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;
        }
      front = textget (i->plist, Qfront_sticky);
      if (! CONSP (front) && ! NILP (front))
        {
          /* All properties are sticky.  We don't split the interval.  */
          tail = Qnil;
          goto check_done;
        }

      /* 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)))
        {
          Lisp_Object prop, tmp;
          prop = XCAR (tail);

          /* Is this particular property front-sticky?  */
          if (CONSP (front) && ! NILP (Fmemq (prop, front)))
            continue;

          /* 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.  */
        }

    check_done:
      /* 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;
        }
    }

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

      if (position == BEG)
        prev = 0;
      else if (eobp)
        {
          prev = i;
          i = 0;
        }
      else
        prev = previous_interval (i);

      /* Even if we are positioned between intervals, we default
         to the left one if it exists.  We extend it now and split
         off a part later, if stickiness demands it.  */
      for (temp = prev ? prev : i; temp; temp = INTERVAL_PARENT_OR_NULL (temp))
        {
          temp->total_length += length;
          temp = balance_possible_root_interval (temp);
        }

      /* If at least one interval has sticky properties,
         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)
        {
          Lisp_Object pleft, pright;
          struct interval newi;

          RESET_INTERVAL (&newi);
          pleft = prev ? prev->plist : Qnil;
          pright = i ? i->plist : Qnil;
          set_interval_plist (&newi, merge_properties_sticky (pleft, pright));

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

          /* We will need to update the cache here later.  */
        }
      else if (! prev && ! NILP (i->plist))
        {
          /* Just split off a new interval at the left.
             Since I wasn't front-sticky, the empty plist is ok.  */
          i = split_interval_left (i, length);
        }
    }

  /* Otherwise just extend the interval.  */
  else
    {
      for (temp = i; temp; temp = INTERVAL_PARENT_OR_NULL (temp))
        {
          temp->total_length += length;
          temp = balance_possible_root_interval (temp);
        }
    }

  return tree;
}

/* Any property might be front-sticky on the left, rear-sticky on the left,
   front-sticky on the right, or rear-sticky on the right; the 16 combinations
   can be arranged in a matrix with rows denoting the left conditions and
   columns denoting the right conditions:
      _  __  _
_     FR FR FR FR
FR__   0  1  2  3
 _FR   4  5  6  7
FR     8  9  A  B
  FR   C  D  E  F

   left-props  = '(front-sticky (p8 p9 pa pb pc pd pe pf)
                   rear-nonsticky (p4 p5 p6 p7 p8 p9 pa pb)
                   p0 L p1 L p2 L p3 L p4 L p5 L p6 L p7 L
                   p8 L p9 L pa L pb L pc L pd L pe L pf L)
   right-props = '(front-sticky (p2 p3 p6 p7 pa pb pe pf)
                   rear-nonsticky (p1 p2 p5 p6 p9 pa pd pe)
                   p0 R p1 R p2 R p3 R p4 R p5 R p6 R p7 R
                   p8 R p9 R pa R pb R pc R pd R pe R pf R)

   We inherit from whoever has a sticky side facing us.  If both sides
   do (cases 2, 3, E, and F), then we inherit from whichever side has a
   non-nil value for the current property.  If both sides do, then we take
   from the left.

   When we inherit a property, we get its stickiness as well as its value.
   So, when we merge the above two lists, we expect to get this:

   result      = '(front-sticky (p6 p7 pa pb pc pd pe pf)
                   rear-nonsticky (p6 pa)
                   p0 L p1 L p2 L p3 L p6 R p7 R
                   pa R pb R pc L pd L pe L pf L)

   The optimizable special cases are:
       left rear-nonsticky = nil, right front-sticky = nil (inherit left)
       left rear-nonsticky = t,   right front-sticky = t   (inherit right)
       left rear-nonsticky = t,   right front-sticky = nil (inherit none)
*/

static Lisp_Object
merge_properties_sticky (Lisp_Object pleft, Lisp_Object pright)
{
  Lisp_Object props, front, rear;
  Lisp_Object lfront, lrear, rfront, rrear;
  Lisp_Object tail1, tail2, sym, lval, rval, cat;
  bool use_left, use_right, lpresent;

  props = Qnil;
  front = Qnil;
  rear  = Qnil;
  lfront = textget (pleft, Qfront_sticky);
  lrear  = textget (pleft, Qrear_nonsticky);
  rfront = textget (pright, Qfront_sticky);
  rrear  = textget (pright, Qrear_nonsticky);

  /* Go through each element of PRIGHT.  */
  for (tail1 = pright; CONSP (tail1); tail1 = Fcdr (XCDR (tail1)))
    {
      Lisp_Object tmp;

      sym = XCAR (tail1);

      /* Sticky properties get special treatment.  */
      if (EQ (sym, Qrear_nonsticky) || EQ (sym, Qfront_sticky))
        continue;

      rval = Fcar (XCDR (tail1));
      for (tail2 = pleft; CONSP (tail2); tail2 = Fcdr (XCDR (tail2)))
        if (EQ (sym, XCAR (tail2)))
          break;

      /* Indicate whether the property is explicitly defined on the left.
         (We know it is defined explicitly on the right
         because otherwise we don't get here.)  */
      lpresent = ! NILP (tail2);
      lval = (NILP (tail2) ? Qnil : Fcar (Fcdr (tail2)));

      /* Even if lrear or rfront say nothing about the stickiness of
         SYM, Vtext_property_default_nonsticky may give default
         stickiness to SYM.  */
      tmp = Fassq (sym, Vtext_property_default_nonsticky);
      use_left = (lpresent
                  && ! (TMEM (sym, lrear)
                        || (CONSP (tmp) && ! NILP (XCDR (tmp)))));
      use_right = (TMEM (sym, rfront)
                   || (CONSP (tmp) && NILP (XCDR (tmp))));
      if (use_left && use_right)
        {
          if (NILP (lval))
            use_left = 0;
          else if (NILP (rval))
            use_right = 0;
        }
      if (use_left)
        {
          /* We build props as (value sym ...) rather than (sym value ...)
             because we plan to nreverse it when we're done.  */
          props = Fcons (lval, Fcons (sym, props));
          if (TMEM (sym, lfront))
            front = Fcons (sym, front);
          if (TMEM (sym, lrear))
            rear = Fcons (sym, rear);
        }
      else if (use_right)
        {
          props = Fcons (rval, Fcons (sym, props));
          if (TMEM (sym, rfront))
            front = Fcons (sym, front);
          if (TMEM (sym, rrear))
            rear = Fcons (sym, rear);
        }
    }

  /* Now go through each element of PLEFT.  */
  for (tail2 = pleft; CONSP (tail2); tail2 = Fcdr (XCDR (tail2)))
    {
      Lisp_Object tmp;

      sym = XCAR (tail2);

      /* Sticky properties get special treatment.  */
      if (EQ (sym, Qrear_nonsticky) || EQ (sym, Qfront_sticky))
        continue;

      /* If sym is in PRIGHT, we've already considered it.  */
      for (tail1 = pright; CONSP (tail1); tail1 = Fcdr (XCDR (tail1)))
        if (EQ (sym, XCAR (tail1)))
          break;
      if (! NILP (tail1))
        continue;

      lval = Fcar (XCDR (tail2));

      /* Even if lrear or rfront say nothing about the stickiness of
         SYM, Vtext_property_default_nonsticky may give default
         stickiness to SYM.  */
      tmp = Fassq (sym, Vtext_property_default_nonsticky);

      /* Since rval is known to be nil in this loop, the test simplifies.  */
      if (! (TMEM (sym, lrear) || (CONSP (tmp) && ! NILP (XCDR (tmp)))))
        {
          props = Fcons (lval, Fcons (sym, props));
          if (TMEM (sym, lfront))
            front = Fcons (sym, front);
        }
      else if (TMEM (sym, rfront) || (CONSP (tmp) && NILP (XCDR (tmp))))
        {
          /* The value is nil, but we still inherit the stickiness
             from the right.  */
          front = Fcons (sym, front);
          if (TMEM (sym, rrear))
            rear = Fcons (sym, rear);
        }
    }
  props = Fnreverse (props);
  if (! NILP (rear))
    props = Fcons (Qrear_nonsticky, Fcons (Fnreverse (rear), props));

  cat = textget (props, Qcategory);
  if (! NILP (front)
      &&
      /* If we have inherited a front-stick category property that is t,
         we don't need to set up a detailed one.  */
      ! (! NILP (cat) && SYMBOLP (cat)
         && EQ (Fget (cat, Qfront_sticky), Qt)))
    props = Fcons (Qfront_sticky, Fcons (Fnreverse (front), props));
  return props;
}

\f
/* Delete a node I from its interval tree by merging its subtrees
   into one subtree which is then returned.  Caller is responsible for
   storing the resulting subtree into its parent.  */

static INTERVAL
delete_node (register INTERVAL i)
{
  register INTERVAL migrate, this;
  register ptrdiff_t migrate_amt;

  if (!i->left)
    return i->right;
  if (!i->right)
    return i->left;

  migrate = i->left;
  migrate_amt = i->left->total_length;
  this = i->right;
  this->total_length += migrate_amt;
  while (this->left)
    {
      this = this->left;
      this->total_length += migrate_amt;
    }
  set_interval_left (this, migrate);
  set_interval_parent (migrate, this);
  eassert (LENGTH (this) > 0);
  eassert (LENGTH (i->right) > 0);

  return i->right;
}

/* Delete interval I from its tree by calling `delete_node'
   and properly connecting the resultant subtree.

   I is presumed to be empty; that is, no adjustments are made
   for the length of I.  */

static void
delete_interval (register INTERVAL i)
{
  register INTERVAL parent;
  ptrdiff_t amt = LENGTH (i);

  eassert (amt == 0);           /* Only used on zero-length intervals now.  */

  if (ROOT_INTERVAL_P (i))
    {
      Lisp_Object owner;
      GET_INTERVAL_OBJECT (owner, i);
      parent = delete_node (i);
      if (parent)
        set_interval_object (parent, owner);

      if (BUFFERP (owner))
        set_buffer_intervals (XBUFFER (owner), parent);
      else if (STRINGP (owner))
        set_string_intervals (owner, parent);
      else
        emacs_abort ();

      return;
    }

  parent = INTERVAL_PARENT (i);
  if (AM_LEFT_CHILD (i))
    {
      set_interval_left (parent, delete_node (i));
      if (parent->left)
        set_interval_parent (parent->left, parent);
    }
  else
    {
      set_interval_right (parent, delete_node (i));
      if (parent->right)
        set_interval_parent (parent->right, parent);
    }
}
\f
/* Find the interval in TREE corresponding to the relative position
   FROM and delete as much as possible of AMOUNT from that interval.
   Return the amount actually deleted, and if the interval was
   zeroed-out, delete that interval node from the tree.

   Note that FROM is actually origin zero, aka relative to the
   leftmost edge of tree.  This is appropriate since we call ourselves
   recursively on subtrees.

   Do this by recursing down TREE to the interval in question, and
   deleting the appropriate amount of text.  */

static ptrdiff_t
interval_deletion_adjustment (register INTERVAL tree, register ptrdiff_t from,
                              register ptrdiff_t amount)
{
  register ptrdiff_t relative_position = from;

  if (!tree)
    return 0;

  /* Left branch.  */
  if (relative_position < LEFT_TOTAL_LENGTH (tree))
    {
      ptrdiff_t subtract = interval_deletion_adjustment (tree->left,
                                                         relative_position,
                                                         amount);
      tree->total_length -= subtract;
      eassert (LENGTH (tree) > 0);
      return subtract;
    }
  /* Right branch.  */
  else if (relative_position >= (TOTAL_LENGTH (tree)
                                 - RIGHT_TOTAL_LENGTH (tree)))
    {
      ptrdiff_t subtract;

      relative_position -= (tree->total_length
                            - RIGHT_TOTAL_LENGTH (tree));
      subtract = interval_deletion_adjustment (tree->right,
                                               relative_position,
                                               amount);
      tree->total_length -= subtract;
      eassert (LENGTH (tree) > 0);
      return subtract;
    }
  /* Here -- this node.  */
  else
    {
      /* How much can we delete from this interval?  */
      ptrdiff_t my_amount = ((tree->total_length
                               - RIGHT_TOTAL_LENGTH (tree))
                              - relative_position);

      if (amount > my_amount)
        amount = my_amount;

      tree->total_length -= amount;
      eassert (LENGTH (tree) >= 0);
      if (LENGTH (tree) == 0)
        delete_interval (tree);

      return amount;
    }

  /* Never reach here.  */
}

/* Effect the adjustments necessary to the interval tree of BUFFER to
   correspond to the deletion of LENGTH characters from that buffer
   text.  The deletion is effected at position START (which is a
   buffer position, i.e. origin 1).  */

static void
adjust_intervals_for_deletion (struct buffer *buffer,
                               ptrdiff_t start, ptrdiff_t length)
{
  ptrdiff_t left_to_delete = length;
  INTERVAL tree = buffer_intervals (buffer);
  Lisp_Object parent;
  ptrdiff_t offset;

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

  if (!tree)
    return;

  eassert (start <= offset + TOTAL_LENGTH (tree)
           && start + length <= offset + TOTAL_LENGTH (tree));

  if (length == TOTAL_LENGTH (tree))
    {
      set_buffer_intervals (buffer, NULL);
      return;
    }

  if (ONLY_INTERVAL_P (tree))
    {
      tree->total_length -= length;
      eassert (LENGTH (tree) > 0);
      return;
    }

  if (start > offset + TOTAL_LENGTH (tree))
    start = offset + TOTAL_LENGTH (tree);
  while (left_to_delete > 0)
    {
      left_to_delete -= interval_deletion_adjustment (tree, start - offset,
                                                      left_to_delete);
      tree = buffer_intervals (buffer);
      if (left_to_delete == tree->total_length)
        {
          set_buffer_intervals (buffer, NULL);
          return;
        }
    }
}
\f
/* Make the adjustments necessary to the interval tree of BUFFER to
   represent an addition or deletion of LENGTH characters starting
   at position START.  Addition or deletion is indicated by the sign
   of LENGTH.  */

void
offset_intervals (struct buffer *buffer, ptrdiff_t start, ptrdiff_t length)
{
  if (!buffer_intervals (buffer) || length == 0)
    return;

  if (length > 0)
    adjust_intervals_for_insertion (buffer_intervals (buffer),
                                    start, length);
  else
    adjust_intervals_for_deletion (buffer, start, -length);
}
\f
/* Merge interval I with its lexicographic successor. The resulting
   interval is returned, and has the properties of the original
   successor.  The properties of I are lost.  I is removed from the
   interval tree.

   IMPORTANT:
   The caller must verify that this is not the last (rightmost)
   interval.  */

static INTERVAL
merge_interval_right (register INTERVAL i)
{
  register ptrdiff_t absorb = LENGTH (i);
  register INTERVAL successor;

  /* Find the succeeding interval.  */
  if (! NULL_RIGHT_CHILD (i))      /* It's below us.  Add absorb
                                      as we descend.  */
    {
      successor = i->right;
      while (! NULL_LEFT_CHILD (successor))
        {
          successor->total_length += absorb;
          eassert (LENGTH (successor) > 0);
          successor = successor->left;
        }

      successor->total_length += absorb;
      eassert (LENGTH (successor) > 0);
      delete_interval (i);
      return successor;
    }

  /* Zero out this interval.  */
  i->total_length -= absorb;
  eassert (TOTAL_LENGTH (i) >= 0);

  successor = i;
  while (! NULL_PARENT (successor))        /* It's above us.  Subtract as
                                              we ascend.  */
    {
      if (AM_LEFT_CHILD (successor))
        {
          successor = INTERVAL_PARENT (successor);
          delete_interval (i);
          return successor;
        }

      successor = INTERVAL_PARENT (successor);
      successor->total_length -= absorb;
      eassert (LENGTH (successor) > 0);
    }

  /* This must be the rightmost or last interval and cannot
     be merged right.  The caller should have known.  */
  emacs_abort ();
}
\f
/* Merge interval I with its lexicographic predecessor. The resulting
   interval is returned, and has the properties of the original predecessor.
   The properties of I are lost.  Interval node I is removed from the tree.

   IMPORTANT:
   The caller must verify that this is not the first (leftmost) interval.  */

INTERVAL
merge_interval_left (register INTERVAL i)
{
  register ptrdiff_t absorb = LENGTH (i);
  register INTERVAL predecessor;

  /* Find the preceding interval.  */
  if (! NULL_LEFT_CHILD (i))    /* It's below us. Go down,
                                   adding ABSORB as we go.  */
    {
      predecessor = i->left;
      while (! NULL_RIGHT_CHILD (predecessor))
        {
          predecessor->total_length += absorb;
          eassert (LENGTH (predecessor) > 0);
          predecessor = predecessor->right;
        }

      predecessor->total_length += absorb;
      eassert (LENGTH (predecessor) > 0);
      delete_interval (i);
      return predecessor;
    }

  /* Zero out this interval.  */
  i->total_length -= absorb;
  eassert (TOTAL_LENGTH (i) >= 0);

  predecessor = i;
  while (! NULL_PARENT (predecessor))   /* It's above us.  Go up,
                                           subtracting ABSORB.  */
    {
      if (AM_RIGHT_CHILD (predecessor))
        {
          predecessor = INTERVAL_PARENT (predecessor);
          delete_interval (i);
          return predecessor;
        }

      predecessor = INTERVAL_PARENT (predecessor);
      predecessor->total_length -= absorb;
      eassert (LENGTH (predecessor) > 0);
    }

  /* This must be the leftmost or first interval and cannot
     be merged left.  The caller should have known.  */
  emacs_abort ();
}
\f
/* Create a copy of SOURCE but with the default value of UP.  */

static INTERVAL
reproduce_interval (INTERVAL source)
{
  register INTERVAL target = make_interval ();

  eassert (LENGTH (source) > 0);

  target->total_length = source->total_length;
  target->position = source->position;

  copy_properties (source, target);

  if (! NULL_LEFT_CHILD (source))
    set_interval_left (target, reproduce_tree (source->left, target));
  if (! NULL_RIGHT_CHILD (source))
    set_interval_right (target, reproduce_tree (source->right, target));

  eassert (LENGTH (target) > 0);
  return target;
}

/* Make an exact copy of interval tree SOURCE which descends from
   PARENT.  This is done by recursing through SOURCE, copying
   the current interval and its properties, and then adjusting
   the pointers of the copy.  */

static INTERVAL
reproduce_tree (INTERVAL source, INTERVAL parent)
{
  INTERVAL target = reproduce_interval (source);
  set_interval_parent (target, parent);
  return target;
}

static INTERVAL
reproduce_tree_obj (INTERVAL source, Lisp_Object parent)
{
  INTERVAL target = reproduce_interval (source);
  set_interval_object (target, parent);
  return target;
}
\f
/* Insert the intervals of SOURCE into BUFFER at POSITION.
   LENGTH is the length of the text in SOURCE.

   The `position' field of the SOURCE intervals is assumed to be
   consistent with its parent; therefore, SOURCE must be an
   interval tree made with copy_interval or must be the whole
   tree of a buffer or a string.

   This is used in insdel.c when inserting Lisp_Strings into the
   buffer.  The text corresponding to SOURCE is already in the buffer
   when this is called.  The intervals of new tree are a copy of those
   belonging to the string being inserted; intervals are never
   shared.

   If the inserted text had no intervals associated, and we don't
   want to inherit the surrounding text's properties, this function
   simply returns -- offset_intervals should handle placing the
   text in the correct interval, depending on the sticky bits.

   If the inserted text had properties (intervals), then there are two
   cases -- either insertion happened in the middle of some interval,
   or between two intervals.

   If the text goes into the middle of an interval, then new intervals
   are created in the middle, and new text has the union of its properties
   and those of the text into which it was inserted.

   If the text goes between two intervals, then if neither interval
   had its appropriate sticky property set (front_sticky, rear_sticky),
   the new text has only its properties.  If one of the sticky properties
   is set, then the new text "sticks" to that region and its properties
   depend on merging as above.  If both the preceding and succeeding
   intervals to the new text are "sticky", then the new text retains
   only its properties, as if neither sticky property were set.  Perhaps
   we should consider merging all three sets of properties onto the new
   text...  */

void
graft_intervals_into_buffer (INTERVAL source, ptrdiff_t position,
                             ptrdiff_t length, struct buffer *buffer,
                             bool inherit)
{
  INTERVAL tree = buffer_intervals (buffer);
  INTERVAL under, over, this;
  ptrdiff_t over_used;

  /* If the new text has no properties, then with inheritance it
     becomes part of whatever interval it was inserted into.
     To prevent inheritance, we must clear out the properties
     of the newly inserted text.  */
  if (!source)
    {
      Lisp_Object buf;
      if (!inherit && tree && length > 0)
        {
          XSETBUFFER (buf, buffer);
          set_text_properties_1 (make_number (position),
                                 make_number (position + length),
                                 Qnil, buf,
                                 find_interval (tree, position));
        }
      /* Shouldn't be necessary.  --Stef  */
      buffer_balance_intervals (buffer);
      return;
    }

  eassert (length == TOTAL_LENGTH (source));

  if ((BUF_Z (buffer) - BUF_BEG (buffer)) == length)
    {
      /* The inserted text constitutes the whole buffer, so
         simply copy over the interval structure.  */
      Lisp_Object buf;

      XSETBUFFER (buf, buffer);
      set_buffer_intervals (buffer, reproduce_tree_obj (source, buf));
      buffer_intervals (buffer)->position = BUF_BEG (buffer);
      eassert (buffer_intervals (buffer)->up_obj == 1);
      return;
    }
  else if (!tree)
    {
      /* Create an interval tree in which to place a copy
         of the intervals of the inserted string.  */
        Lisp_Object buf;

        XSETBUFFER (buf, buffer);
        tree = create_root_interval (buf);
    }
  /* Paranoia -- the text has already been added, so
     this buffer should be of non-zero length.  */
  eassert (TOTAL_LENGTH (tree) > 0);

  this = under = find_interval (tree, position);
  eassert (under);
  over = find_interval (source, interval_start_pos (source));

  /* Here for insertion in the middle of an interval.
     Split off an equivalent interval to the right,
     then don't bother with it any more.  */

  if (position > under->position)
    {
      INTERVAL end_unchanged
        = split_interval_left (this, position - under->position);
      copy_properties (under, end_unchanged);
      under->position = position;
    }
  else
    {
      /* This call may have some effect because previous_interval may
         update `position' fields of intervals.  Thus, don't ignore it
         for the moment.  Someone please tell me the truth (K.Handa).  */
      INTERVAL prev = previous_interval (under);
      (void) prev;
#if 0
      /* But, this code surely has no effect.  And, anyway,
         END_NONSTICKY_P is unreliable now.  */
      if (prev && !END_NONSTICKY_P (prev))
        prev = 0;
#endif /* 0 */
    }

  /* Insertion is now at beginning of UNDER.  */

  /* The inserted text "sticks" to the interval `under',
     which means it gets those properties.
     The properties of under are the result of
     adjust_intervals_for_insertion, so stickiness has
     already been taken care of.  */

  /* OVER is the interval we are copying from next.
     OVER_USED says how many characters' worth of OVER
     have already been copied into target intervals.
     UNDER is the next interval in the target.  */
  over_used = 0;
  while (over)
    {
      /* If UNDER is longer than OVER, split it.  */
      if (LENGTH (over) - over_used < LENGTH (under))
        {
          this = split_interval_left (under, LENGTH (over) - over_used);
          copy_properties (under, this);
        }
      else
        this = under;

      /* THIS is now the interval to copy or merge into.
         OVER covers all of it.  */
      if (inherit)
        merge_properties (over, this);
      else
        copy_properties (over, this);

      /* If THIS and OVER end at the same place,
         advance OVER to a new source interval.  */
      if (LENGTH (this) == LENGTH (over) - over_used)
        {
          over = next_interval (over);
          over_used = 0;
        }
      else
        /* Otherwise just record that more of OVER has been used.  */
        over_used += LENGTH (this);

      /* Always advance to a new target interval.  */
      under = next_interval (this);
    }

  buffer_balance_intervals (buffer);
}

/* Get the value of property PROP from PLIST,
   which is the plist of an interval.
   We check for direct properties, for categories with property PROP,
   and for PROP appearing on the default-text-properties list.  */

Lisp_Object
textget (Lisp_Object plist, register Lisp_Object prop)
{
  return lookup_char_property (plist, prop, 1);
}

Lisp_Object
lookup_char_property (Lisp_Object plist, Lisp_Object prop, bool textprop)
{
  Lisp_Object tail, fallback = Qnil;

  for (tail = plist; CONSP (tail); tail = Fcdr (XCDR (tail)))
    {
      register Lisp_Object tem;
      tem = XCAR (tail);
      if (EQ (prop, tem))
        return Fcar (XCDR (tail));
      if (EQ (tem, Qcategory))
        {
          tem = Fcar (XCDR (tail));
          if (SYMBOLP (tem))
            fallback = Fget (tem, prop);
        }
    }

  if (! NILP (fallback))
    return fallback;
  /* Check for alternative properties.  */
  tail = Fassq (prop, Vchar_property_alias_alist);
  if (! NILP (tail))
    {
      tail = XCDR (tail);
      for (; NILP (fallback) && CONSP (tail); tail = XCDR (tail))
        fallback = Fplist_get (plist, XCAR (tail));
    }

  if (textprop && NILP (fallback) && CONSP (Vdefault_text_properties))
    fallback = Fplist_get (Vdefault_text_properties, prop);
  return fallback;
}

\f
/* Set point in BUFFER "temporarily" to CHARPOS, which corresponds to
   byte position BYTEPOS.  */

void
temp_set_point_both (struct buffer *buffer,
                     ptrdiff_t charpos, ptrdiff_t bytepos)
{
  /* In a single-byte buffer, the two positions must be equal.  */
  eassert (BUF_ZV (buffer) != BUF_ZV_BYTE (buffer) || charpos == bytepos);

  eassert (charpos <= bytepos);
  eassert (charpos <= BUF_ZV (buffer) || BUF_BEGV (buffer) <= charpos);

  SET_BUF_PT_BOTH (buffer, charpos, bytepos);
}

/* Set point "temporarily", without checking any text properties.  */

void
temp_set_point (struct buffer *buffer, ptrdiff_t charpos)
{
  temp_set_point_both (buffer, charpos,
                       buf_charpos_to_bytepos (buffer, charpos));
}

/* Set point in BUFFER to CHARPOS.  If the target position is
   before an intangible character, move to an ok place.  */

void
set_point (ptrdiff_t charpos)
{
  set_point_both (charpos, buf_charpos_to_bytepos (current_buffer, charpos));
}

/* Set PT from MARKER's clipped position.  */

void
set_point_from_marker (Lisp_Object marker)
{
  ptrdiff_t charpos = clip_to_bounds (BEGV, marker_position (marker), ZV);
  ptrdiff_t bytepos = marker_byte_position (marker);

  /* Don't trust the byte position if the marker belongs to a
     different buffer.  */
  if (XMARKER (marker)->buffer != current_buffer)
    bytepos = buf_charpos_to_bytepos (current_buffer, charpos);
  else
    bytepos = clip_to_bounds (BEGV_BYTE, bytepos, ZV_BYTE);
  set_point_both (charpos, bytepos);
}

/* If there's an invisible character at position POS + TEST_OFFS in the
   current buffer, and the invisible property has a `stickiness' such that
   inserting a character at position POS would inherit the property it,
   return POS + ADJ, otherwise return POS.  If TEST_INTANG, intangibility
   is required as well as invisibility.

   TEST_OFFS should be either 0 or -1, and ADJ should be either 1 or -1.

   Note that `stickiness' is determined by overlay marker insertion types,
   if the invisible property comes from an overlay.  */

static ptrdiff_t
adjust_for_invis_intang (ptrdiff_t pos, ptrdiff_t test_offs, ptrdiff_t adj,
                         bool test_intang)
{
  Lisp_Object invis_propval, invis_overlay;
  Lisp_Object test_pos;

  if ((adj < 0 && pos + adj < BEGV) || (adj > 0 && pos + adj > ZV))
    /* POS + ADJ would be beyond the buffer bounds, so do no adjustment.  */
    return pos;

  test_pos = make_number (pos + test_offs);

  invis_propval
    = get_char_property_and_overlay (test_pos, Qinvisible, Qnil,
                                     &invis_overlay);

  if ((!test_intang
       || ! NILP (Fget_char_property (test_pos, Qintangible, Qnil)))
      && TEXT_PROP_MEANS_INVISIBLE (invis_propval)
      /* This next test is true if the invisible property has a stickiness
         such that an insertion at POS would inherit it.  */
      && (NILP (invis_overlay)
          /* Invisible property is from a text-property.  */
          ? (text_property_stickiness (Qinvisible, make_number (pos), Qnil)
             == (test_offs == 0 ? 1 : -1))
          /* Invisible property is from an overlay.  */
          : (test_offs == 0
             ? XMARKER (OVERLAY_START (invis_overlay))->insertion_type == 0
             : XMARKER (OVERLAY_END (invis_overlay))->insertion_type == 1)))
    pos += adj;

  return pos;
}

/* Set point in BUFFER to CHARPOS, which corresponds to byte
   position BYTEPOS.  If the target position is
   before an intangible character, move to an ok place.  */

void
set_point_both (ptrdiff_t charpos, ptrdiff_t bytepos)
{
  register INTERVAL to, from, toprev, fromprev;
  ptrdiff_t buffer_point;
  ptrdiff_t old_position = PT;
  /* This ensures that we move forward past intangible text when the
     initial position is the same as the destination, in the rare
     instances where this is important, e.g. in line-move-finish
     (simple.el).  */
  bool backwards = charpos < old_position;
  bool have_overlays;
  ptrdiff_t original_position;

  bset_point_before_scroll (current_buffer, Qnil);

  if (charpos == PT)
    return;

  /* In a single-byte buffer, the two positions must be equal.  */
  eassert (ZV != ZV_BYTE || charpos == bytepos);

  /* Check this now, before checking if the buffer has any intervals.
     That way, we can catch conditions which break this sanity check
     whether or not there are intervals in the buffer.  */
  eassert (charpos <= ZV && charpos >= BEGV);

  have_overlays = buffer_has_overlays ();

  /* If we have no text properties and overlays,
     then we can do it quickly.  */
  if (!buffer_intervals (current_buffer) && ! have_overlays)
    {
      temp_set_point_both (current_buffer, charpos, bytepos);
      return;
    }

  /* Set TO to the interval containing the char after CHARPOS,
     and TOPREV to the interval containing the char before CHARPOS.
     Either one may be null.  They may be equal.  */
  to = find_interval (buffer_intervals (current_buffer), charpos);
  if (charpos == BEGV)
    toprev = 0;
  else if (to && to->position == charpos)
    toprev = previous_interval (to);
  else
    toprev = to;

  buffer_point = (PT == ZV ? ZV - 1 : PT);

  /* Set FROM to the interval containing the char after PT,
     and FROMPREV to the interval containing the char before PT.
     Either one may be null.  They may be equal.  */
  /* We could cache this and save time.  */
  from = find_interval (buffer_intervals (current_buffer), buffer_point);
  if (buffer_point == BEGV)
    fromprev = 0;
  else if (from && from->position == PT)
    fromprev = previous_interval (from);
  else if (buffer_point != PT)
    fromprev = from, from = 0;
  else
    fromprev = from;

  /* Moving within an interval.  */
  if (to == from && toprev == fromprev && INTERVAL_VISIBLE_P (to)
      && ! have_overlays)
    {
      temp_set_point_both (current_buffer, charpos, bytepos);
      return;
    }

  original_position = charpos;

  /* If the new position is between two intangible characters
     with the same intangible property value,
     move forward or backward until a change in that property.  */
  if (NILP (Vinhibit_point_motion_hooks)
      && ((to && toprev)
          || have_overlays)
      /* Intangibility never stops us from positioning at the beginning
         or end of the buffer, so don't bother checking in that case.  */
      && charpos != BEGV && charpos != ZV)
    {
      Lisp_Object pos;
      Lisp_Object intangible_propval;

      if (backwards)
        {
          /* If the preceding character is both intangible and invisible,
             and the invisible property is `rear-sticky', perturb it so
             that the search starts one character earlier -- this ensures
             that point can never move to the end of an invisible/
             intangible/rear-sticky region.  */
          charpos = adjust_for_invis_intang (charpos, -1, -1, 1);

          XSETINT (pos, charpos);

          /* If following char is intangible,
             skip back over all chars with matching intangible property.  */

          intangible_propval = Fget_char_property (pos, Qintangible, Qnil);

          if (! NILP (intangible_propval))
            {
              while (XINT (pos) > BEGV
                     && EQ (Fget_char_property (make_number (XINT (pos) - 1),
                                                Qintangible, Qnil),
                            intangible_propval))
                pos = Fprevious_char_property_change (pos, Qnil);

              /* Set CHARPOS from POS, and if the final intangible character
                 that we skipped over is also invisible, and the invisible
                 property is `front-sticky', perturb it to be one character
                 earlier -- this ensures that point can never move to the
                 beginning of an invisible/intangible/front-sticky region.  */
              charpos = adjust_for_invis_intang (XINT (pos), 0, -1, 0);
            }
        }
      else
        {
          /* If the following character is both intangible and invisible,
             and the invisible property is `front-sticky', perturb it so
             that the search starts one character later -- this ensures
             that point can never move to the beginning of an
             invisible/intangible/front-sticky region.  */
          charpos = adjust_for_invis_intang (charpos, 0, 1, 1);

          XSETINT (pos, charpos);

          /* If preceding char is intangible,
             skip forward over all chars with matching intangible property.  */

          intangible_propval = Fget_char_property (make_number (charpos - 1),
                                                   Qintangible, Qnil);

          if (! NILP (intangible_propval))
            {
              while (XINT (pos) < ZV
                     && EQ (Fget_char_property (pos, Qintangible, Qnil),
                            intangible_propval))
                pos = Fnext_char_property_change (pos, Qnil);

              /* Set CHARPOS from POS, and if the final intangible character
                 that we skipped over is also invisible, and the invisible
                 property is `rear-sticky', perturb it to be one character
                 later -- this ensures that point can never move to the
                 end of an invisible/intangible/rear-sticky region.  */
              charpos = adjust_for_invis_intang (XINT (pos), -1, 1, 0);
            }
        }

      bytepos = buf_charpos_to_bytepos (current_buffer, charpos);
    }

  if (charpos != original_position)
    {
      /* Set TO to the interval containing the char after CHARPOS,
         and TOPREV to the interval containing the char before CHARPOS.
         Either one may be null.  They may be equal.  */
      to = find_interval (buffer_intervals (current_buffer), charpos);
      if (charpos == BEGV)
        toprev = 0;
      else if (to && to->position == charpos)
        toprev = previous_interval (to);
      else
        toprev = to;
    }

  /* Here TO is the interval after the stopping point
     and TOPREV is the interval before the stopping point.
     One or the other may be null.  */

  temp_set_point_both (current_buffer, charpos, bytepos);

  /* We run point-left and point-entered hooks here, if the
     two intervals are not equivalent.  These hooks take
     (old_point, new_point) as arguments.  */
  if (NILP (Vinhibit_point_motion_hooks)
      && (! intervals_equal (from, to)
          || ! intervals_equal (fromprev, toprev)))
    {
      Lisp_Object leave_after, leave_before, enter_after, enter_before;

      if (fromprev)
        leave_before = textget (fromprev->plist, Qpoint_left);
      else
        leave_before = Qnil;

      if (from)
        leave_after = textget (from->plist, Qpoint_left);
      else
        leave_after = Qnil;

      if (toprev)
        enter_before = textget (toprev->plist, Qpoint_entered);
      else
        enter_before = Qnil;

      if (to)
        enter_after = textget (to->plist, Qpoint_entered);
      else
        enter_after = Qnil;

      if (! EQ (leave_before, enter_before) && !NILP (leave_before))
        call2 (leave_before, make_number (old_position),
               make_number (charpos));
      if (! EQ (leave_after, enter_after) && !NILP (leave_after))
        call2 (leave_after, make_number (old_position),
               make_number (charpos));

      if (! EQ (enter_before, leave_before) && !NILP (enter_before))
        call2 (enter_before, make_number (old_position),
               make_number (charpos));
      if (! EQ (enter_after, leave_after) && !NILP (enter_after))
        call2 (enter_after, make_number (old_position),
               make_number (charpos));
    }
}
\f
/* Move point to POSITION, unless POSITION is inside an intangible
   segment that reaches all the way to point.  */

void
move_if_not_intangible (ptrdiff_t position)
{
  Lisp_Object pos;
  Lisp_Object intangible_propval;

  XSETINT (pos, position);

  if (! NILP (Vinhibit_point_motion_hooks))
    /* If intangible is inhibited, always move point to POSITION.  */
    ;
  else if (PT < position && XINT (pos) < ZV)
    {
      /* We want to move forward, so check the text before POSITION.  */

      intangible_propval = Fget_char_property (pos,
                                               Qintangible, Qnil);

      /* If following char is intangible,
         skip back over all chars with matching intangible property.  */
      if (! NILP (intangible_propval))
        while (XINT (pos) > BEGV
               && EQ (Fget_char_property (make_number (XINT (pos) - 1),
                                          Qintangible, Qnil),
                      intangible_propval))
          pos = Fprevious_char_property_change (pos, Qnil);
    }
  else if (XINT (pos) > BEGV)
    {
      /* We want to move backward, so check the text after POSITION.  */

      intangible_propval = Fget_char_property (make_number (XINT (pos) - 1),
                                               Qintangible, Qnil);

      /* If following char is intangible,
         skip forward over all chars with matching intangible property.  */
      if (! NILP (intangible_propval))
        while (XINT (pos) < ZV
               && EQ (Fget_char_property (pos, Qintangible, Qnil),
                      intangible_propval))
          pos = Fnext_char_property_change (pos, Qnil);

    }
  else if (position < BEGV)
    position = BEGV;
  else if (position > ZV)
    position = ZV;

  /* If the whole stretch between PT and POSITION isn't intangible,
     try moving to POSITION (which means we actually move farther
     if POSITION is inside of intangible text).  */

  if (XINT (pos) != PT)
    SET_PT (position);
}
\f
/* If text at position POS has property PROP, set *VAL to the property
   value, *START and *END to the beginning and end of a region that
   has the same property, and return true.  Otherwise return false.

   OBJECT is the string or buffer to look for the property in;
   nil means the current buffer. */

bool
get_property_and_range (ptrdiff_t pos, Lisp_Object prop, Lisp_Object *val,
                        ptrdiff_t *start, ptrdiff_t *end, Lisp_Object object)
{
  INTERVAL i, prev, next;

  if (NILP (object))
    i = find_interval (buffer_intervals (current_buffer), pos);
  else if (BUFFERP (object))
    i = find_interval (buffer_intervals (XBUFFER (object)), pos);
  else if (STRINGP (object))
    i = find_interval (string_intervals (object), pos);
  else
    emacs_abort ();

  if (!i || (i->position + LENGTH (i) <= pos))
    return 0;
  *val = textget (i->plist, prop);
  if (NILP (*val))
    return 0;

  next = i;                     /* remember it in advance */
  prev = previous_interval (i);
  while (prev
         && EQ (*val, textget (prev->plist, prop)))
    i = prev, prev = previous_interval (prev);
  *start = i->position;

  next = next_interval (i);
  while (next && EQ (*val, textget (next->plist, prop)))
    i = next, next = next_interval (next);
  *end = i->position + LENGTH (i);

  return 1;
}
\f
/* Return the proper local keymap TYPE for position POSITION in
   BUFFER; TYPE should be one of `keymap' or `local-map'.  Use the map
   specified by the PROP property, if any.  Otherwise, if TYPE is
   `local-map' use BUFFER's local map.  */

Lisp_Object
get_local_map (ptrdiff_t position, struct buffer *buffer, Lisp_Object type)
{
  Lisp_Object prop, lispy_position, lispy_buffer;
  ptrdiff_t old_begv, old_zv, old_begv_byte, old_zv_byte;
  ptrdiff_t count = SPECPDL_INDEX ();

  position = clip_to_bounds (BUF_BEGV (buffer), position, BUF_ZV (buffer));

  /* Ignore narrowing, so that a local map continues to be valid even if
     the visible region contains no characters and hence no properties.  */
  old_begv = BUF_BEGV (buffer);
  old_zv = BUF_ZV (buffer);
  old_begv_byte = BUF_BEGV_BYTE (buffer);
  old_zv_byte = BUF_ZV_BYTE (buffer);

  specbind (Qinhibit_quit, Qt);
  SET_BUF_BEGV_BOTH (buffer, BUF_BEG (buffer), BUF_BEG_BYTE (buffer));
  SET_BUF_ZV_BOTH (buffer, BUF_Z (buffer), BUF_Z_BYTE (buffer));

  XSETFASTINT (lispy_position, position);
  XSETBUFFER (lispy_buffer, buffer);
  /* First check if the CHAR has any property.  This is because when
     we click with the mouse, the mouse pointer is really pointing
     to the CHAR after POS.  */
  prop = Fget_char_property (lispy_position, type, lispy_buffer);
  /* If not, look at the POS's properties.  This is necessary because when
     editing a field with a `local-map' property, we want insertion at the end
     to obey the `local-map' property.  */
  if (NILP (prop))
    prop = Fget_pos_property (lispy_position, type, lispy_buffer);

  SET_BUF_BEGV_BOTH (buffer, old_begv, old_begv_byte);
  SET_BUF_ZV_BOTH (buffer, old_zv, old_zv_byte);
  unbind_to (count, Qnil);

  /* Use the local map only if it is valid.  */
  prop = get_keymap (prop, 0, 0);
  if (CONSP (prop))
    return prop;

  if (EQ (type, Qkeymap))
    return Qnil;
  else
    return BVAR (buffer, keymap);
}
\f
/* Produce an interval tree reflecting the intervals in
   TREE from START to START + LENGTH.
   The new interval tree has no parent and has a starting-position of 0.  */

INTERVAL
copy_intervals (INTERVAL tree, ptrdiff_t start, ptrdiff_t length)
{
  register INTERVAL i, new, t;
  register ptrdiff_t got, prevlen;

  if (!tree || length <= 0)
    return NULL;

  i = find_interval (tree, start);
  eassert (i && LENGTH (i) > 0);

  /* If there is only one interval and it's the default, return nil.  */
  if ((start - i->position + 1 + length) < LENGTH (i)
      && DEFAULT_INTERVAL_P (i))
    return NULL;

  new = make_interval ();
  new->position = 0;
  got = (LENGTH (i) - (start - i->position));
  new->total_length = length;
  eassert (TOTAL_LENGTH (new) >= 0);
  copy_properties (i, new);

  t = new;
  prevlen = got;
  while (got < length)
    {
      i = next_interval (i);
      t = split_interval_right (t, prevlen);
      copy_properties (i, t);
      prevlen = LENGTH (i);
      got += prevlen;
    }

  return balance_an_interval (new);
}

/* Give STRING the properties of BUFFER from POSITION to LENGTH.  */

void
copy_intervals_to_string (Lisp_Object string, struct buffer *buffer,
                          ptrdiff_t position, ptrdiff_t length)
{
  INTERVAL interval_copy = copy_intervals (buffer_intervals (buffer),
                                           position, length);
  if (!interval_copy)
    return;

  set_interval_object (interval_copy, string);
  set_string_intervals (string, interval_copy);
}
\f
/* Return true if strings S1 and S2 have identical properties.
   Assume they have identical characters.  */

bool
compare_string_intervals (Lisp_Object s1, Lisp_Object s2)
{
  INTERVAL i1, i2;
  ptrdiff_t pos = 0;
  ptrdiff_t end = SCHARS (s1);

  i1 = find_interval (string_intervals (s1), 0);
  i2 = find_interval (string_intervals (s2), 0);

  while (pos < end)
    {
      /* Determine how far we can go before we reach the end of I1 or I2.  */
      ptrdiff_t len1 = (i1 != 0 ? INTERVAL_LAST_POS (i1) : end) - pos;
      ptrdiff_t len2 = (i2 != 0 ? INTERVAL_LAST_POS (i2) : end) - pos;
      ptrdiff_t distance = min (len1, len2);

      /* If we ever find a mismatch between the strings,
         they differ.  */
      if (! intervals_equal (i1, i2))
        return 0;

      /* Advance POS till the end of the shorter interval,
         and advance one or both interval pointers for the new position.  */
      pos += distance;
      if (len1 == distance)
        i1 = next_interval (i1);
      if (len2 == distance)
        i2 = next_interval (i2);
    }
  return 1;
}
\f
/* Recursively adjust interval I in the current buffer
   for setting enable_multibyte_characters to MULTI_FLAG.
   The range of interval I is START ... END in characters,
   START_BYTE ... END_BYTE in bytes.  */

static void
set_intervals_multibyte_1 (INTERVAL i, bool multi_flag,
                           ptrdiff_t start, ptrdiff_t start_byte,
                           ptrdiff_t end, ptrdiff_t end_byte)
{
  /* Fix the length of this interval.  */
  if (multi_flag)
    i->total_length = end - start;
  else
    i->total_length = end_byte - start_byte;
  eassert (TOTAL_LENGTH (i) >= 0);

  if (TOTAL_LENGTH (i) == 0)
    {
      delete_interval (i);
      return;
    }

  /* Recursively fix the length of the subintervals.  */
  if (i->left)
    {
      ptrdiff_t left_end, left_end_byte;

      if (multi_flag)
        {
          ptrdiff_t temp;
          left_end_byte = start_byte + LEFT_TOTAL_LENGTH (i);
          left_end = BYTE_TO_CHAR (left_end_byte);

          temp = CHAR_TO_BYTE (left_end);

          /* If LEFT_END_BYTE is in the middle of a character,
             adjust it and LEFT_END to a char boundary.  */
          if (left_end_byte > temp)
            {
              left_end_byte = temp;
            }
          if (left_end_byte < temp)
            {
              left_end--;
              left_end_byte = CHAR_TO_BYTE (left_end);
            }
        }
      else
        {
          left_end = start + LEFT_TOTAL_LENGTH (i);
          left_end_byte = CHAR_TO_BYTE (left_end);
        }

      set_intervals_multibyte_1 (i->left, multi_flag, start, start_byte,
                                 left_end, left_end_byte);
    }
  if (i->right)
    {
      ptrdiff_t right_start_byte, right_start;

      if (multi_flag)
        {
          ptrdiff_t temp;

          right_start_byte = end_byte - RIGHT_TOTAL_LENGTH (i);
          right_start = BYTE_TO_CHAR (right_start_byte);

          /* If RIGHT_START_BYTE is in the middle of a character,
             adjust it and RIGHT_START to a char boundary.  */
          temp = CHAR_TO_BYTE (right_start);

          if (right_start_byte < temp)
            {
              right_start_byte = temp;
            }
          if (right_start_byte > temp)
            {
              right_start++;
              right_start_byte = CHAR_TO_BYTE (right_start);
            }
        }
      else
        {
          right_start = end - RIGHT_TOTAL_LENGTH (i);
          right_start_byte = CHAR_TO_BYTE (right_start);
        }

      set_intervals_multibyte_1 (i->right, multi_flag,
                                 right_start, right_start_byte,
                                 end, end_byte);
    }

  /* Rounding to char boundaries can theoretically make this interval
     spurious.  If so, delete one child, and copy its property list
     to this interval.  */
  if (LEFT_TOTAL_LENGTH (i) + RIGHT_TOTAL_LENGTH (i) >= TOTAL_LENGTH (i))
    {
      if ((i)->left)
        {
          set_interval_plist (i, i->left->plist);
          (i)->left->total_length = 0;
          delete_interval ((i)->left);
        }
      else
        {
          set_interval_plist (i, i->right->plist);
          (i)->right->total_length = 0;
          delete_interval ((i)->right);
        }
    }
}

/* Update the intervals of the current buffer
   to fit the contents as multibyte (if MULTI_FLAG)
   or to fit them as non-multibyte (if not MULTI_FLAG).  */

void
set_intervals_multibyte (bool multi_flag)
{
  INTERVAL i = buffer_intervals (current_buffer);

  if (i)
    set_intervals_multibyte_1 (i, multi_flag, BEG, BEG_BYTE, Z, Z_BYTE);
}