Cleanup intervals.

* intervals.h (NULL_INTERVAL, DEFAULT_INTERVAL): Remove.
(NULL_INTERVAL_P): Likewise.  Adjust users.
(FRONT_STICKY_P, END_NONSTICKY_P, FRONT_NONSTICKY_P): Adjust
comment.  Move under #if 0.
* alloc.c, buffer.c, editfns.c, fns.c, insdel.c, intervals.c:
* print.c, syntax.c, textprop.c, xdisp.c: Adjust users.

13 files changed, 191 insertions, 196 deletions

diff --git a/src/ChangeLog b/src/ChangeLog
index 7c49694dd44..7919b6f8f8a 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,5 +1,15 @@
 2012-08-08  Dmitry Antipov  <dmantipov@yandex.ru>
 
+	Cleanup intervals.
+	* intervals.h (NULL_INTERVAL, DEFAULT_INTERVAL): Remove.
+	(NULL_INTERVAL_P): Likewise.  Adjust users.
+	(FRONT_STICKY_P, END_NONSTICKY_P, FRONT_NONSTICKY_P): Adjust
+	comment.  Move under #if 0.
+	* alloc.c, buffer.c, editfns.c, fns.c, insdel.c, intervals.c:
+	* print.c, syntax.c, textprop.c, xdisp.c: Adjust users.
+
+2012-08-08  Dmitry Antipov  <dmantipov@yandex.ru>
+
 	Check total length of intervals with eassert.
 	* intervals.h (CHECK_TOTAL_LENGTH): Remove.
 	* intervals.c: Change all users to eassert.
diff --git a/src/alloc.c b/src/alloc.c
index b6fe6fa2eb3..d342a722ca6 100644
--- a/src/alloc.c
+++ b/src/alloc.c
@@ -1559,19 +1559,20 @@ mark_interval_tree (register INTERVAL tree)
 
 /* Mark the interval tree rooted in I.  */
 
-#define MARK_INTERVAL_TREE(i)				\
-  do {							\
-    if (!NULL_INTERVAL_P (i) && !i->gcmarkbit)		\
-      mark_interval_tree (i);				\
+#define MARK_INTERVAL_TREE(i)	\
+  do {				\
+    if (i && !i->gcmarkbit)	\
+      mark_interval_tree (i);	\
   } while (0)
 
+/* Unmark and rebalance interval tree rooted in I.  */
 
-#define UNMARK_BALANCE_INTERVALS(i)			\
-  do {							\
-   if (! NULL_INTERVAL_P (i))				\
-     (i) = balance_intervals (i);			\
+#define UNMARK_BALANCE_INTERVALS(i)	\
+  do {					\
+   if (i)				\
+     (i) = balance_intervals (i);	\
   } while (0)
-
+
 /***********************************************************************
 			  String Allocation
  ***********************************************************************/
@@ -2100,7 +2101,7 @@ sweep_strings (void)
 		  /* String is live; unmark it and its intervals.  */
 		  UNMARK_STRING (s);
 
-		  if (!NULL_INTERVAL_P (s->intervals))
+		  if (s->intervals)
 		    UNMARK_BALANCE_INTERVALS (s->intervals);
 
 		  ++total_strings;
@@ -2502,7 +2503,7 @@ make_uninit_multibyte_string (EMACS_INT nchars, EMACS_INT nbytes)
     return empty_multibyte_string;
 
   s = allocate_string ();
-  s->intervals = NULL_INTERVAL;
+  s->intervals = NULL;
   allocate_string_data (s, nchars, nbytes);
   XSETSTRING (string, s);
   string_chars_consed += nbytes;
@@ -5221,7 +5222,7 @@ make_pure_string (const char *data,
     }
   s->size = nchars;
   s->size_byte = multibyte ? nbytes : -1;
-  s->intervals = NULL_INTERVAL;
+  s->intervals = NULL;
   XSETSTRING (string, s);
   return string;
 }
@@ -5237,7 +5238,7 @@ make_pure_c_string (const char *data, ptrdiff_t nchars)
   s->size = nchars;
   s->size_byte = -1;
   s->data = (unsigned char *) data;
-  s->intervals = NULL_INTERVAL;
+  s->intervals = NULL;
   XSETSTRING (string, s);
   return string;
 }
diff --git a/src/buffer.c b/src/buffer.c
index 7d0e1b641a2..ad28b69b972 100644
--- a/src/buffer.c
+++ b/src/buffer.c
@@ -360,7 +360,7 @@ even if it is dead.  The return value is never nil.  */)
   BUF_CHARS_MODIFF (b) = 1;
   BUF_OVERLAY_MODIFF (b) = 1;
   BUF_SAVE_MODIFF (b) = 1;
-  BUF_INTERVALS (b) = 0;
+  BUF_INTERVALS (b) = NULL;
   BUF_UNCHANGED_MODIFIED (b) = 1;
   BUF_OVERLAY_UNCHANGED_MODIFIED (b) = 1;
   BUF_END_UNCHANGED (b) = 0;
@@ -384,7 +384,7 @@ even if it is dead.  The return value is never nil.  */)
   BVAR (b, zv_marker) = Qnil;
 
   name = Fcopy_sequence (buffer_or_name);
-  STRING_SET_INTERVALS (name, NULL_INTERVAL);
+  STRING_SET_INTERVALS (name, NULL);
   BVAR (b, name) = name;
 
   BVAR (b, undo_list) = (SREF (name, 0) != ' ') ? Qnil : Qt;
@@ -589,7 +589,7 @@ CLONE nil means the indirect buffer's state is reset to default values.  */)
   all_buffers = b;
 
   name = Fcopy_sequence (name);
-  STRING_SET_INTERVALS (name, NULL_INTERVAL);
+  STRING_SET_INTERVALS (name, NULL);
   BVAR (b, name) = name;
 
   reset_buffer (b);
@@ -1688,7 +1688,7 @@ cleaning up all windows currently displaying the buffer to be killed. */)
 	  m = next;
 	}
       BUF_MARKERS (b) = NULL;
-      BUF_INTERVALS (b) = NULL_INTERVAL;
+      BUF_INTERVALS (b) = NULL;
 
       /* Perhaps we should explicitly free the interval tree here... */
     }
@@ -4904,8 +4904,8 @@ init_buffer_once (void)
   /* No one will share the text with these buffers, but let's play it safe.  */
   buffer_defaults.indirections = 0;
   buffer_local_symbols.indirections = 0;
-  BUF_INTERVALS (&buffer_defaults) = 0;
-  BUF_INTERVALS (&buffer_local_symbols) = 0;
+  BUF_INTERVALS (&buffer_defaults) = NULL;
+  BUF_INTERVALS (&buffer_local_symbols) = NULL;
   XSETPVECTYPESIZE (&buffer_defaults, PVEC_BUFFER, pvecsize);
   XSETBUFFER (Vbuffer_defaults, &buffer_defaults);
   XSETPVECTYPESIZE (&buffer_local_symbols, PVEC_BUFFER, pvecsize);
diff --git a/src/editfns.c b/src/editfns.c
index ae568a40a68..9d74563ca9d 100644
--- a/src/editfns.c
+++ b/src/editfns.c
@@ -4637,7 +4637,7 @@ Transposing beyond buffer boundaries is an error.  */)
       /* Don't use Fset_text_properties: that can cause GC, which can
 	 clobber objects stored in the tmp_intervals.  */
       tmp_interval3 = validate_interval_range (buf, &startr1, &endr2, 0);
-      if (!NULL_INTERVAL_P (tmp_interval3))
+      if (tmp_interval3)
 	set_text_properties_1 (startr1, endr2, Qnil, buf, tmp_interval3);
 
       /* First region smaller than second.  */
@@ -4696,11 +4696,11 @@ Transposing beyond buffer boundaries is an error.  */)
           tmp_interval2 = copy_intervals (cur_intv, start2, len2);
 
 	  tmp_interval3 = validate_interval_range (buf, &startr1, &endr1, 0);
-	  if (!NULL_INTERVAL_P (tmp_interval3))
+	  if (tmp_interval3)
 	    set_text_properties_1 (startr1, endr1, Qnil, buf, tmp_interval3);
 
 	  tmp_interval3 = validate_interval_range (buf, &startr2, &endr2, 0);
-	  if (!NULL_INTERVAL_P (tmp_interval3))
+	  if (tmp_interval3)
 	    set_text_properties_1 (startr2, endr2, Qnil, buf, tmp_interval3);
 
 	  temp = SAFE_ALLOCA (len1_byte);
@@ -4729,7 +4729,7 @@ Transposing beyond buffer boundaries is an error.  */)
           tmp_interval2 = copy_intervals (cur_intv, start2, len2);
 
 	  tmp_interval3 = validate_interval_range (buf, &startr1, &endr2, 0);
-	  if (!NULL_INTERVAL_P (tmp_interval3))
+	  if (tmp_interval3)
 	    set_text_properties_1 (startr1, endr2, Qnil, buf, tmp_interval3);
 
 	  /* holds region 2 */
@@ -4762,7 +4762,7 @@ Transposing beyond buffer boundaries is an error.  */)
           tmp_interval2 = copy_intervals (cur_intv, start2, len2);
 
 	  tmp_interval3 = validate_interval_range (buf, &startr1, &endr2, 0);
-	  if (!NULL_INTERVAL_P (tmp_interval3))
+	  if (tmp_interval3)
 	    set_text_properties_1 (startr1, endr2, Qnil, buf, tmp_interval3);
 
 	  /* holds region 1 */
diff --git a/src/fileio.c b/src/fileio.c
index 36d61f15617..7639c2f0b33 100644
--- a/src/fileio.c
+++ b/src/fileio.c
@@ -3145,7 +3145,7 @@ decide_coding_unwind (Lisp_Object unwind_data)
     set_buffer_internal (XBUFFER (buffer));
   adjust_markers_for_delete (BEG, BEG_BYTE, Z, Z_BYTE);
   adjust_overlays_for_delete (BEG, Z - BEG);
-  BUF_INTERVALS (current_buffer) = 0;
+  BUF_INTERVALS (current_buffer) = NULL;
   TEMP_SET_PT_BOTH (BEG, BEG_BYTE);
 
   /* Now we are safe to change the buffer's multibyteness directly.  */
diff --git a/src/fns.c b/src/fns.c
index 8496d2de937..7da9be2c85e 100644
--- a/src/fns.c
+++ b/src/fns.c
@@ -628,7 +628,7 @@ concat (ptrdiff_t nargs, Lisp_Object *args,
 	  ptrdiff_t thislen_byte = SBYTES (this);
 
 	  memcpy (SDATA (val) + toindex_byte, SDATA (this), SBYTES (this));
-	  if (! NULL_INTERVAL_P (STRING_INTERVALS (this)))
+	  if (STRING_INTERVALS (this))
 	    {
 	      textprops[num_textprops].argnum = argnum;
 	      textprops[num_textprops].from = 0;
@@ -640,7 +640,7 @@ concat (ptrdiff_t nargs, Lisp_Object *args,
       /* Copy a single-byte string to a multibyte string.  */
       else if (STRINGP (this) && STRINGP (val))
 	{
-	  if (! NULL_INTERVAL_P (STRING_INTERVALS (this)))
+	  if (STRING_INTERVALS (this))
 	    {
 	      textprops[num_textprops].argnum = argnum;
 	      textprops[num_textprops].from = 0;
@@ -1060,7 +1060,7 @@ If you're not sure, whether to use `string-as-multibyte' or
 	str_as_multibyte (SDATA (new_string), nbytes,
 			  SBYTES (string), NULL);
       string = new_string;
-      STRING_SET_INTERVALS (string, NULL_INTERVAL);
+      STRING_SET_INTERVALS (string, NULL);
     }
   return string;
 }
diff --git a/src/insdel.c b/src/insdel.c
index 9646507bc4b..6cd46ac634b 100644
--- a/src/insdel.c
+++ b/src/insdel.c
@@ -844,10 +844,10 @@ insert_1_both (const char *string,
 			     PT + nchars, PT_BYTE + nbytes,
 			     before_markers);
 
-  if (BUF_INTERVALS (current_buffer) != 0)
+  if (BUF_INTERVALS (current_buffer))
     offset_intervals (current_buffer, PT, nchars);
 
-  if (!inherit && BUF_INTERVALS (current_buffer) != 0)
+  if (!inherit && BUF_INTERVALS (current_buffer))
     set_text_properties (make_number (PT), make_number (PT + nchars),
 			 Qnil, Qnil, Qnil);
 
@@ -1017,10 +1017,10 @@ insert_from_gap (ptrdiff_t nchars, ptrdiff_t nbytes)
   adjust_markers_for_insert (GPT - nchars, GPT_BYTE - nbytes,
 			     GPT, GPT_BYTE, 0);
 
-  if (BUF_INTERVALS (current_buffer) != 0)
+  if (BUF_INTERVALS (current_buffer))
     {
       offset_intervals (current_buffer, GPT - nchars, nchars);
-      graft_intervals_into_buffer (NULL_INTERVAL, GPT - nchars, nchars,
+      graft_intervals_into_buffer (NULL, GPT - nchars, nchars,
 				   current_buffer, 0);
     }
 
@@ -1157,7 +1157,7 @@ insert_from_buffer_1 (struct buffer *buf,
 			     PT_BYTE + outgoing_nbytes,
 			     0);
 
-  if (BUF_INTERVALS (current_buffer) != 0)
+  if (BUF_INTERVALS (current_buffer))
     offset_intervals (current_buffer, PT, nchars);
 
   /* Get the intervals for the part of the string we are inserting.  */
@@ -1225,7 +1225,7 @@ adjust_after_replace (ptrdiff_t from, ptrdiff_t from_byte,
     adjust_overlays_for_insert (from, len - nchars_del);
   else if (len < nchars_del)
     adjust_overlays_for_delete (from, nchars_del - len);
-  if (BUF_INTERVALS (current_buffer) != 0)
+  if (BUF_INTERVALS (current_buffer))
     {
       offset_intervals (current_buffer, from, len - nchars_del);
     }
@@ -1823,7 +1823,7 @@ prepare_to_modify_buffer (ptrdiff_t start, ptrdiff_t end,
   if (XBUFFER (XWINDOW (selected_window)->buffer) != current_buffer)
     ++windows_or_buffers_changed;
 
-  if (BUF_INTERVALS (current_buffer) != 0)
+  if (BUF_INTERVALS (current_buffer))
     {
       if (preserve_ptr)
 	{
diff --git a/src/intervals.c b/src/intervals.c
index 40f77f3957a..504557dadb7 100644
--- a/src/intervals.c
+++ b/src/intervals.c
@@ -207,10 +207,10 @@ void
 traverse_intervals_noorder (INTERVAL tree, void (*function) (INTERVAL, Lisp_Object), Lisp_Object arg)
 {
   /* Minimize stack usage.  */
-  while (!NULL_INTERVAL_P (tree))
+  while (tree)
     {
       (*function) (tree, arg);
-      if (NULL_INTERVAL_P (tree->right))
+      if (!tree->right)
 	tree = tree->left;
       else
 	{
@@ -227,7 +227,7 @@ void
 traverse_intervals (INTERVAL tree, ptrdiff_t position,
 		    void (*function) (INTERVAL, Lisp_Object), Lisp_Object arg)
 {
-  while (!NULL_INTERVAL_P (tree))
+  while (tree)
     {
       traverse_intervals (tree->left, position, function, arg);
       position += LEFT_TOTAL_LENGTH (tree);
@@ -262,7 +262,7 @@ search_for_interval (INTERVAL i, INTERVAL tree)
 {
   icount = 0;
   search_interval = i;
-  found_interval = NULL_INTERVAL;
+  found_interval = NULL;
   traverse_intervals_noorder (tree, &check_for_interval, Qnil);
   return found_interval;
 }
@@ -333,7 +333,7 @@ rotate_right (INTERVAL interval)
 
   /* Make A point to c */
   interval_set_left (interval, i);
-  if (! NULL_INTERVAL_P (i))
+  if (i)
     interval_set_parent (i, interval);
 
   /* A's total length is decreased by the length of B and its left child.  */
@@ -380,7 +380,7 @@ rotate_left (INTERVAL interval)
 
   /* Make A point to c */
   interval_set_right (interval, i);
-  if (! NULL_INTERVAL_P (i))
+  if (i)
     interval_set_parent (i, interval);
 
   /* A's total length is decreased by the length of B and its right child.  */
@@ -480,12 +480,9 @@ balance_intervals_internal (register INTERVAL tree)
 INTERVAL
 balance_intervals (INTERVAL tree)
 {
-  if (tree == NULL_INTERVAL)
-    return NULL_INTERVAL;
-
-  return balance_intervals_internal (tree);
+  return tree ? balance_intervals_internal (tree) : NULL;
 }
-
+
 /* 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
@@ -589,7 +586,7 @@ interval_start_pos (INTERVAL source)
 {
   Lisp_Object parent;
 
-  if (NULL_INTERVAL_P (source))
+  if (!source)
     return 0;
 
   if (! INTERVAL_HAS_OBJECT (source))
@@ -617,8 +614,8 @@ find_interval (register INTERVAL tree, register ptrdiff_t position)
                     to POSITION.  */
   register ptrdiff_t relative_position;
 
-  if (NULL_INTERVAL_P (tree))
-    return NULL_INTERVAL;
+  if (!tree)
+    return NULL;
 
   relative_position = position;
   if (INTERVAL_HAS_OBJECT (tree))
@@ -669,8 +666,8 @@ next_interval (register INTERVAL interval)
   register INTERVAL i = interval;
   register ptrdiff_t next_position;
 
-  if (NULL_INTERVAL_P (i))
-    return NULL_INTERVAL;
+  if (!i)
+    return NULL;
   next_position = interval->position + LENGTH (interval);
 
   if (! NULL_RIGHT_CHILD (i))
@@ -695,7 +692,7 @@ next_interval (register INTERVAL interval)
       i = INTERVAL_PARENT (i);
     }
 
-  return NULL_INTERVAL;
+  return NULL;
 }
 
 /* Find the preceding interval (lexicographically) to INTERVAL.
@@ -707,8 +704,8 @@ previous_interval (register INTERVAL interval)
 {
   register INTERVAL i;
 
-  if (NULL_INTERVAL_P (interval))
-    return NULL_INTERVAL;
+  if (!interval)
+    return NULL;
 
   if (! NULL_LEFT_CHILD (interval))
     {
@@ -733,7 +730,7 @@ previous_interval (register INTERVAL interval)
       i = INTERVAL_PARENT (i);
     }
 
-  return NULL_INTERVAL;
+  return NULL;
 }
 
 /* Find the interval containing POS given some non-NULL INTERVAL
@@ -744,8 +741,8 @@ previous_interval (register INTERVAL interval)
 INTERVAL
 update_interval (register INTERVAL i, ptrdiff_t pos)
 {
-  if (NULL_INTERVAL_P (i))
-    return NULL_INTERVAL;
+  if (!i)
+    return NULL;
 
   while (1)
     {
@@ -938,8 +935,8 @@ adjust_intervals_for_insertion (INTERVAL tree,
 	  struct interval newi;
 
 	  RESET_INTERVAL (&newi);
-	  pleft = NULL_INTERVAL_P (prev) ? Qnil : prev->plist;
-	  pright = NULL_INTERVAL_P (i) ? Qnil : i->plist;
+	  pleft = prev ? prev->plist : Qnil;
+	  pright = i ? i->plist : Qnil;
 	  interval_set_plist (&newi, merge_properties_sticky (pleft, pright));
 
 	  if (! prev) /* i.e. position == BEG */
@@ -954,8 +951,7 @@ adjust_intervals_for_insertion (INTERVAL tree,
 	    {
 	      prev = split_interval_right (prev, position - prev->position);
 	      interval_set_plist (prev, newi.plist);
-	      if (! NULL_INTERVAL_P (i)
-		  && intervals_equal (prev, i))
+	      if (i && intervals_equal (prev, i))
 		merge_interval_right (prev);
 	    }
 
@@ -1164,16 +1160,16 @@ delete_node (register INTERVAL i)
   register INTERVAL migrate, this;
   register ptrdiff_t migrate_amt;
 
-  if (NULL_INTERVAL_P (i->left))
+  if (!i->left)
     return i->right;
-  if (NULL_INTERVAL_P (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 (! NULL_INTERVAL_P (this->left))
+  while (this->left)
     {
       this = this->left;
       this->total_length += migrate_amt;
@@ -1204,7 +1200,7 @@ delete_interval (register INTERVAL i)
       Lisp_Object owner;
       GET_INTERVAL_OBJECT (owner, i);
       parent = delete_node (i);
-      if (! NULL_INTERVAL_P (parent))
+      if (parent)
 	interval_set_object (parent, owner);
 
       if (BUFFERP (owner))
@@ -1221,13 +1217,13 @@ delete_interval (register INTERVAL i)
   if (AM_LEFT_CHILD (i))
     {
       interval_set_left (parent, delete_node (i));
-      if (! NULL_INTERVAL_P (parent->left))
+      if (parent->left)
 	interval_set_parent (parent->left, parent);
     }
   else
     {
       interval_set_right (parent, delete_node (i));
-      if (! NULL_INTERVAL_P (parent->right))
+      if (parent->right)
 	interval_set_parent (parent->right, parent);
     }
 }
@@ -1250,7 +1246,7 @@ interval_deletion_adjustment (register INTERVAL tree, register ptrdiff_t from,
 {
   register ptrdiff_t relative_position = from;
 
-  if (NULL_INTERVAL_P (tree))
+  if (!tree)
     return 0;
 
   /* Left branch.  */
@@ -1317,7 +1313,7 @@ adjust_intervals_for_deletion (struct buffer *buffer,
   GET_INTERVAL_OBJECT (parent, tree);
   offset = (BUFFERP (parent) ? BUF_BEG (XBUFFER (parent)) : 0);
 
-  if (NULL_INTERVAL_P (tree))
+  if (!tree)
     return;
 
   eassert (start <= offset + TOTAL_LENGTH (tree)
@@ -1325,7 +1321,7 @@ adjust_intervals_for_deletion (struct buffer *buffer,
 
   if (length == TOTAL_LENGTH (tree))
     {
-      BUF_INTERVALS (buffer) = NULL_INTERVAL;
+      BUF_INTERVALS (buffer) = NULL;
       return;
     }
 
@@ -1345,7 +1341,7 @@ adjust_intervals_for_deletion (struct buffer *buffer,
       tree = BUF_INTERVALS (buffer);
       if (left_to_delete == tree->total_length)
 	{
-	  BUF_INTERVALS (buffer) = NULL_INTERVAL;
+	  BUF_INTERVALS (buffer) = NULL;
 	  return;
 	}
     }
@@ -1363,7 +1359,7 @@ adjust_intervals_for_deletion (struct buffer *buffer,
 void
 offset_intervals (struct buffer *buffer, ptrdiff_t start, ptrdiff_t length)
 {
-  if (NULL_INTERVAL_P (BUF_INTERVALS (buffer)) || length == 0)
+  if (!BUF_INTERVALS (buffer) || length == 0)
     return;
 
   if (length > 0)
@@ -1580,17 +1576,17 @@ graft_intervals_into_buffer (INTERVAL source, ptrdiff_t position,
      becomes part of whatever interval it was inserted into.
      To prevent inheritance, we must clear out the properties
      of the newly inserted text.  */
-  if (NULL_INTERVAL_P (source))
+  if (!source)
     {
       Lisp_Object buf;
-      if (!inherit && !NULL_INTERVAL_P (tree) && length > 0)
+      if (!inherit && tree && length > 0)
 	{
 	  XSETBUFFER (buf, buffer);
 	  set_text_properties_1 (make_number (position),
 				 make_number (position + length),
 				 Qnil, buf, 0);
 	}
-      if (! NULL_INTERVAL_P (BUF_INTERVALS (buffer)))
+      if (BUF_INTERVALS (buffer))
 	/* Shouldn't be necessary.  --Stef  */
 	BUF_INTERVALS (buffer) = balance_an_interval (BUF_INTERVALS (buffer));
       return;
@@ -1608,7 +1604,7 @@ graft_intervals_into_buffer (INTERVAL source, ptrdiff_t position,
       eassert (BUF_INTERVALS (buffer)->up_obj == 1);
 	  return;
 	}
-  else if (NULL_INTERVAL_P (tree))
+  else if (!tree)
     { /* Create an interval tree in which to place a copy
 	 of the intervals of the inserted string.  */
 	Lisp_Object buf;
@@ -1620,7 +1616,7 @@ graft_intervals_into_buffer (INTERVAL source, ptrdiff_t position,
   eassert (TOTAL_LENGTH (tree) > 0);
 
   this = under = find_interval (tree, position);
-  eassert (!NULL_INTERVAL_P (under));
+  eassert (under);
   over = find_interval (source, interval_start_pos (source));
 
   /* Here for insertion in the middle of an interval.
@@ -1662,7 +1658,7 @@ graft_intervals_into_buffer (INTERVAL source, ptrdiff_t position,
      have already been copied into target intervals.
      UNDER is the next interval in the target.  */
   over_used = 0;
-  while (! NULL_INTERVAL_P (over))
+  while (over)
     {
       /* If UNDER is longer than OVER, split it.  */
       if (LENGTH (over) - over_used < LENGTH (under))
@@ -1695,7 +1691,7 @@ graft_intervals_into_buffer (INTERVAL source, ptrdiff_t position,
       under = next_interval (this);
     }
 
-  if (! NULL_INTERVAL_P (BUF_INTERVALS (buffer)))
+  if (BUF_INTERVALS (buffer))
     BUF_INTERVALS (buffer) = balance_an_interval (BUF_INTERVALS (buffer));
   return;
 }
@@ -1864,7 +1860,7 @@ set_point_both (ptrdiff_t charpos, ptrdiff_t bytepos)
 
   /* If we have no text properties and overlays,
      then we can do it quickly.  */
-  if (NULL_INTERVAL_P (BUF_INTERVALS (current_buffer)) && ! have_overlays)
+  if (!BUF_INTERVALS (current_buffer) && ! have_overlays)
     {
       temp_set_point_both (current_buffer, charpos, bytepos);
       return;
@@ -1911,7 +1907,7 @@ set_point_both (ptrdiff_t charpos, ptrdiff_t bytepos)
      with the same intangible property value,
      move forward or backward until a change in that property.  */
   if (NILP (Vinhibit_point_motion_hooks)
-      && ((! NULL_INTERVAL_P (to) && ! NULL_INTERVAL_P (toprev))
+      && ((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.  */
@@ -2134,7 +2130,7 @@ get_property_and_range (ptrdiff_t pos, Lisp_Object prop, Lisp_Object *val,
   else
     abort ();
 
-  if (NULL_INTERVAL_P (i) || (i->position + LENGTH (i) <= pos))
+  if (!i || (i->position + LENGTH (i) <= pos))
     return 0;
   *val = textget (i->plist, prop);
   if (NILP (*val))
@@ -2142,14 +2138,13 @@ get_property_and_range (ptrdiff_t pos, Lisp_Object prop, Lisp_Object *val,
 
   next = i;			/* remember it in advance */
   prev = previous_interval (i);
-  while (! NULL_INTERVAL_P (prev)
+  while (prev
 	 && EQ (*val, textget (prev->plist, prop)))
     i = prev, prev = previous_interval (prev);
   *start = i->position;
 
   next = next_interval (i);
-  while (! NULL_INTERVAL_P (next)
-	 && EQ (*val, textget (next->plist, prop)))
+  while (next && EQ (*val, textget (next->plist, prop)))
     i = next, next = next_interval (next);
   *end = i->position + LENGTH (i);
 
@@ -2220,16 +2215,16 @@ copy_intervals (INTERVAL tree, ptrdiff_t start, ptrdiff_t length)
   register INTERVAL i, new, t;
   register ptrdiff_t got, prevlen;
 
-  if (NULL_INTERVAL_P (tree) || length <= 0)
-    return NULL_INTERVAL;
+  if (!tree || length <= 0)
+    return NULL;
 
   i = find_interval (tree, start);
-  eassert (!NULL_INTERVAL_P (i) && LENGTH (i) > 0);
+  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_INTERVAL;
+    return NULL;
 
   new = make_interval ();
   new->position = 0;
@@ -2260,7 +2255,7 @@ copy_intervals_to_string (Lisp_Object string, struct buffer *buffer,
 {
   INTERVAL interval_copy = copy_intervals (BUF_INTERVALS (buffer),
 					   position, length);
-  if (NULL_INTERVAL_P (interval_copy))
+  if (!interval_copy)
     return;
 
   interval_set_object (interval_copy, string);
diff --git a/src/intervals.h b/src/intervals.h
index fa9fe8d6fdb..b50016eeb59 100644
--- a/src/intervals.h
+++ b/src/intervals.h
@@ -20,9 +20,6 @@ along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
 
 INLINE_HEADER_BEGIN
 
-#define NULL_INTERVAL ((INTERVAL)0)
-#define INTERVAL_DEFAULT NULL_INTERVAL
-
 /* Basic data type for use of intervals.  */
 
 struct interval
@@ -63,28 +60,25 @@ struct interval
 
 /* These are macros for dealing with the interval tree.  */
 
-#define NULL_INTERVAL_P(i) ((i) == NULL_INTERVAL)
-
 /* True if this interval has no right child.  */
-#define NULL_RIGHT_CHILD(i) ((i)->right == NULL_INTERVAL)
+#define NULL_RIGHT_CHILD(i) ((i)->right == NULL)
 
 /* True if this interval has no left child.  */
-#define NULL_LEFT_CHILD(i) ((i)->left == NULL_INTERVAL)
+#define NULL_LEFT_CHILD(i) ((i)->left == NULL)
 
 /* True if this interval has no parent.  */
 #define NULL_PARENT(i) ((i)->up_obj || (i)->up.interval == 0)
 
 /* True if this interval is the left child of some other interval.  */
-#define AM_LEFT_CHILD(i) (! NULL_PARENT (i) \
-			  && INTERVAL_PARENT (i)->left == (i))
+#define AM_LEFT_CHILD(i)					\
+  (! NULL_PARENT (i) && INTERVAL_PARENT (i)->left == (i))
 
 /* True if this interval is the right child of some other interval.  */
-#define AM_RIGHT_CHILD(i) (! NULL_PARENT (i) \
-			   && INTERVAL_PARENT (i)->right == (i))
+#define AM_RIGHT_CHILD(i)					\
+  (! NULL_PARENT (i) && INTERVAL_PARENT (i)->right == (i))
 
 /* True if this interval has no children.  */
-#define LEAF_INTERVAL_P(i) ((i)->left == NULL_INTERVAL \
-			    && (i)->right == NULL_INTERVAL)
+#define LEAF_INTERVAL_P(i) ((i)->left == NULL && (i)->right == NULL)
 
 /* True if this interval has no parent and is therefore the root.  */
 #define ROOT_INTERVAL_P(i) (NULL_PARENT (i))
@@ -93,17 +87,16 @@ struct interval
 #define ONLY_INTERVAL_P(i) (ROOT_INTERVAL_P ((i)) && LEAF_INTERVAL_P ((i)))
 
 /* True if this interval has both left and right children.  */
-#define BOTH_KIDS_P(i) ((i)->left != NULL_INTERVAL     \
-			&& (i)->right != NULL_INTERVAL)
+#define BOTH_KIDS_P(i) ((i)->left != NULL && (i)->right != NULL)
 
 /* The total size of all text represented by this interval and all its
    children in the tree.   This is zero if the interval is null.  */
-#define TOTAL_LENGTH(i) ((i) == NULL_INTERVAL ? 0 : (i)->total_length)
+#define TOTAL_LENGTH(i) ((i) == NULL ? 0 : (i)->total_length)
 
 /* The size of text represented by this interval alone.  */
-#define LENGTH(i) ((i) == NULL_INTERVAL ? 0 : (TOTAL_LENGTH ((i))          \
-					       - TOTAL_LENGTH ((i)->right) \
-					       - TOTAL_LENGTH ((i)->left)))
+#define LENGTH(i) ((i) == NULL ? 0 : (TOTAL_LENGTH ((i))		\
+				      - TOTAL_LENGTH ((i)->right)	\
+				      - TOTAL_LENGTH ((i)->left)))
 
 /* The position of the character just past the end of I.  Note that
    the position cache i->position must be valid for this to work.  */
@@ -115,15 +108,14 @@ struct interval
 /* The total size of the right subtree of this interval.  */
 #define RIGHT_TOTAL_LENGTH(i) ((i)->right ? (i)->right->total_length : 0)
 
-
 /* These macros are for dealing with the interval properties.  */
 
 /* True if this is a default interval, which is the same as being null
    or having no properties.  */
-#define DEFAULT_INTERVAL_P(i) (NULL_INTERVAL_P (i) || EQ ((i)->plist, Qnil))
+#define DEFAULT_INTERVAL_P(i) (!i || EQ ((i)->plist, Qnil))
 
 /* Test what type of parent we have.  Three possibilities: another
-   interval, a buffer or string object, or NULL_INTERVAL.  */
+   interval, a buffer or string object, or NULL.  */
 #define INTERVAL_HAS_PARENT(i) ((i)->up_obj == 0 && (i)->up.interval != 0)
 #define INTERVAL_HAS_OBJECT(i) ((i)->up_obj)
 
@@ -187,7 +179,7 @@ interval_copy_parent (INTERVAL d, INTERVAL s)
 
 /* Get the parent interval, if any, otherwise a null pointer.  Useful
    for walking up to the root in a "for" loop; use this to get the
-   "next" value, and test the result to see if it's NULL_INTERVAL.  */
+   "next" value, and test the result to see if it's NULL.  */
 #define INTERVAL_PARENT_OR_NULL(i) \
    (INTERVAL_HAS_PARENT (i) ? INTERVAL_PARENT (i) : 0)
 
@@ -195,8 +187,8 @@ interval_copy_parent (INTERVAL d, INTERVAL s)
 #define RESET_INTERVAL(i)		      \
 {					      \
   (i)->total_length = (i)->position = 0;      \
-  (i)->left = (i)->right = NULL_INTERVAL;     \
-  interval_set_parent (i, NULL_INTERVAL);     \
+  (i)->left = (i)->right = NULL;	      \
+  interval_set_parent (i, NULL);	      \
   (i)->write_protect = 0;		      \
   (i)->visible = 0;			      \
   (i)->front_sticky = (i)->rear_sticky = 0;   \
@@ -232,39 +224,36 @@ interval_copy_parent (INTERVAL d, INTERVAL s)
 
 /* Is this interval visible?  Replace later with cache access.  */
 #define INTERVAL_VISIBLE_P(i) \
-  (! NULL_INTERVAL_P (i) && NILP (textget ((i)->plist, Qinvisible)))
+  (i && NILP (textget ((i)->plist, Qinvisible)))
 
 /* Is this interval writable?  Replace later with cache access.  */
 #define INTERVAL_WRITABLE_P(i)					\
-  (! NULL_INTERVAL_P (i)					\
-   && (NILP (textget ((i)->plist, Qread_only))			\
-       || ((CONSP (Vinhibit_read_only)				\
-	    ? !NILP (Fmemq (textget ((i)->plist, Qread_only),	\
-			    Vinhibit_read_only))		\
-	    : !NILP (Vinhibit_read_only)))))			\
+  (i && (NILP (textget ((i)->plist, Qread_only))		\
+	 || ((CONSP (Vinhibit_read_only)			\
+	      ? !NILP (Fmemq (textget ((i)->plist, Qread_only),	\
+			      Vinhibit_read_only))		\
+	      : !NILP (Vinhibit_read_only)))))			\
 
 /* Macros to tell whether insertions before or after this interval
-   should stick to it.  */
-/* Replace later with cache access */
-/*#define FRONT_STICKY_P(i) ((i)->front_sticky != 0)
-  #define END_STICKY_P(i) ((i)->rear_sticky != 0)*/
-/* As we now have Vtext_property_default_nonsticky, these macros are
-   unreliable now.  Currently, they are never used.  */
-#define FRONT_STICKY_P(i) \
-  (! NULL_INTERVAL_P (i) && ! NILP (textget ((i)->plist, Qfront_sticky)))
-#define END_NONSTICKY_P(i) \
-  (! NULL_INTERVAL_P (i) && ! NILP (textget ((i)->plist, Qrear_nonsticky)))
-#define FRONT_NONSTICKY_P(i) \
-  (! NULL_INTERVAL_P (i) && ! EQ (Qt, textget ((i)->plist, Qfront_sticky)))
-
+   should stick to it.  Now we have Vtext_property_default_nonsticky,
+   so these macros are unreliable now and never used.  */
+
+#if 0
+#define FRONT_STICKY_P(i)				\
+  (i && ! NILP (textget ((i)->plist, Qfront_sticky)))
+#define END_NONSTICKY_P(i)				\
+  (i && ! NILP (textget ((i)->plist, Qrear_nonsticky)))
+#define FRONT_NONSTICKY_P(i)				\
+  (i && ! EQ (Qt, textget ((i)->plist, Qfront_sticky)))
+#endif
 
 /* If PROP is the `invisible' property of a character,
    this is 1 if the character should be treated as invisible,
    and 2 if it is invisible but with an ellipsis.  */
 
-#define TEXT_PROP_MEANS_INVISIBLE(prop)				\
+#define TEXT_PROP_MEANS_INVISIBLE(prop)					\
   (EQ (BVAR (current_buffer, invisibility_spec), Qt)			\
-   ? !NILP (prop)						\
+   ? !NILP (prop)							\
    : invisible_p (prop, BVAR (current_buffer, invisibility_spec)))
 
 /* Declared in alloc.c.  */
diff --git a/src/print.c b/src/print.c
index 4a8c3fda319..1e9f237ee82 100644
--- a/src/print.c
+++ b/src/print.c
@@ -1408,7 +1408,7 @@ print_object (Lisp_Object obj, register Lisp_Object printcharfun, int escapeflag
 	  if (! EQ (Vprint_charset_text_property, Qt))
 	    obj = print_prune_string_charset (obj);
 
-	  if (!NULL_INTERVAL_P (STRING_INTERVALS (obj)))
+	  if (STRING_INTERVALS (obj))
 	    {
 	      PRINTCHAR ('#');
 	      PRINTCHAR ('(');
@@ -1499,7 +1499,7 @@ print_object (Lisp_Object obj, register Lisp_Object printcharfun, int escapeflag
 	    }
 	  PRINTCHAR ('\"');
 
-	  if (!NULL_INTERVAL_P (STRING_INTERVALS (obj)))
+	  if (STRING_INTERVALS (obj))
 	    {
 	      traverse_intervals (STRING_INTERVALS (obj),
 				  0, print_interval, printcharfun);
diff --git a/src/syntax.c b/src/syntax.c
index 1299d2e9931..c031c2b07af 100644
--- a/src/syntax.c
+++ b/src/syntax.c
@@ -171,7 +171,7 @@ struct gl_state_s gl_state;		/* Global state of syntax parser.  */
    direction than the intervals - or in an interval.  We update the
    current syntax-table basing on the property of this interval, and
    update the interval to start further than CHARPOS - or be
-   NULL_INTERVAL.  We also update lim_property to be the next value of
+   NULL.  We also update lim_property to be the next value of
    charpos to call this subroutine again - or be before/after the
    start/end of OBJECT.  */
 
@@ -192,7 +192,7 @@ update_syntax_table (ptrdiff_t charpos, EMACS_INT count, int init,
       i = interval_of (charpos, object);
       gl_state.backward_i = gl_state.forward_i = i;
       invalidate = 0;
-      if (NULL_INTERVAL_P (i))
+      if (!i)
 	return;
       /* interval_of updates only ->position of the return value, so
 	 update the parents manually to speed up update_interval.  */
@@ -217,7 +217,7 @@ update_syntax_table (ptrdiff_t charpos, EMACS_INT count, int init,
 
   /* We are guaranteed to be called with CHARPOS either in i,
      or further off.  */
-  if (NULL_INTERVAL_P (i))
+  if (!i)
     error ("Error in syntax_table logic for to-the-end intervals");
   else if (charpos < i->position)		/* Move left.  */
     {
@@ -287,7 +287,7 @@ update_syntax_table (ptrdiff_t charpos, EMACS_INT count, int init,
 	}
     }
 
-  while (!NULL_INTERVAL_P (i))
+  while (i)
     {
       if (cnt && !EQ (tmp_table, textget (i->plist, Qsyntax_table)))
 	{
@@ -313,7 +313,7 @@ update_syntax_table (ptrdiff_t charpos, EMACS_INT count, int init,
 		/* e_property at EOB is not set to ZV but to ZV+1, so that
 		   we can do INC(from);UPDATE_SYNTAX_TABLE_FORWARD without
 		   having to check eob between the two.  */
-		+ (NULL_INTERVAL_P (next_interval (i)) ? 1 : 0);
+		+ (next_interval (i) ? 0 : 1);
 	      gl_state.forward_i = i;
 	    }
 	  else
@@ -326,7 +326,7 @@ update_syntax_table (ptrdiff_t charpos, EMACS_INT count, int init,
       cnt++;
       i = count > 0 ? next_interval (i) : previous_interval (i);
     }
-  eassert (NULL_INTERVAL_P (i)); /* This property goes to the end.  */
+  eassert (i == NULL); /* This property goes to the end.  */
   if (count > 0)
     gl_state.e_property = gl_state.stop;
   else
diff --git a/src/textprop.c b/src/textprop.c
index 5b390fbfe08..1ec1ab11d2e 100644
--- a/src/textprop.c
+++ b/src/textprop.c
@@ -105,7 +105,7 @@ text_read_only (Lisp_Object propval)
    Fprevious_property_change which call this function with BEGIN == END.
    Handle this case specially.
 
-   If FORCE is soft (0), it's OK to return NULL_INTERVAL.  Otherwise,
+   If FORCE is soft (0), it's OK to return NULL.  Otherwise,
    create an interval tree for OBJECT if one doesn't exist, provided
    the object actually contains text.  In the current design, if there
    is no text, there can be no text properties.  */
@@ -126,7 +126,7 @@ validate_interval_range (Lisp_Object object, Lisp_Object *begin, Lisp_Object *en
   /* If we are asked for a point, but from a subr which operates
      on a range, then return nothing.  */
   if (EQ (*begin, *end) && begin != end)
-    return NULL_INTERVAL;
+    return NULL;
 
   if (XINT (*begin) > XINT (*end))
     {
@@ -147,7 +147,7 @@ validate_interval_range (Lisp_Object object, Lisp_Object *begin, Lisp_Object *en
 
       /* If there's no text, there are no properties.  */
       if (BUF_BEGV (b) == BUF_ZV (b))
-	return NULL_INTERVAL;
+	return NULL;
 
       searchpos = XINT (*begin);
     }
@@ -164,12 +164,12 @@ validate_interval_range (Lisp_Object object, Lisp_Object *begin, Lisp_Object *en
       i = STRING_INTERVALS (object);
 
       if (len == 0)
-	return NULL_INTERVAL;
+	return NULL;
 
       searchpos = XINT (*begin);
     }
 
-  if (NULL_INTERVAL_P (i))
+  if (!i)
     return (force ? create_root_interval (object) : i);
 
   return find_interval (i, searchpos);
@@ -500,7 +500,7 @@ interval_of (ptrdiff_t position, Lisp_Object object)
   if (NILP (object))
     XSETBUFFER (object, current_buffer);
   else if (EQ (object, Qt))
-    return NULL_INTERVAL;
+    return NULL;
 
   CHECK_STRING_OR_BUFFER (object);
 
@@ -521,8 +521,8 @@ interval_of (ptrdiff_t position, Lisp_Object object)
 
   if (!(beg <= position && position <= end))
     args_out_of_range (make_number (position), make_number (position));
-  if (beg == end || NULL_INTERVAL_P (i))
-    return NULL_INTERVAL;
+  if (beg == end || !i)
+    return NULL;
 
   return find_interval (i, position);
 }
@@ -542,7 +542,7 @@ If POSITION is at the end of OBJECT, the value is nil.  */)
     XSETBUFFER (object, current_buffer);
 
   i = validate_interval_range (object, &position, &position, soft);
-  if (NULL_INTERVAL_P (i))
+  if (!i)
     return Qnil;
   /* If POSITION is at the end of the interval,
      it means it's the end of OBJECT.
@@ -922,12 +922,12 @@ past position LIMIT; return LIMIT if nothing is found before LIMIT.  */)
      bother checking further intervals.  */
   if (EQ (limit, Qt))
     {
-      if (NULL_INTERVAL_P (i))
+      if (!i)
 	next = i;
       else
 	next = next_interval (i);
 
-      if (NULL_INTERVAL_P (next))
+      if (!next)
 	XSETFASTINT (position, (STRINGP (object)
 				? SCHARS (object)
 				: BUF_ZV (XBUFFER (object))));
@@ -936,16 +936,16 @@ past position LIMIT; return LIMIT if nothing is found before LIMIT.  */)
       return position;
     }
 
-  if (NULL_INTERVAL_P (i))
+  if (!i)
     return limit;
 
   next = next_interval (i);
 
-  while (!NULL_INTERVAL_P (next) && intervals_equal (i, next)
+  while (next && intervals_equal (i, next)
 	 && (NILP (limit) || next->position < XFASTINT (limit)))
     next = next_interval (next);
 
-  if (NULL_INTERVAL_P (next)
+  if (!next
       || (next->position
 	  >= (INTEGERP (limit)
 	      ? XFASTINT (limit)
@@ -983,17 +983,17 @@ past position LIMIT; return LIMIT if nothing is found before LIMIT.  */)
     CHECK_NUMBER_COERCE_MARKER (limit);
 
   i = validate_interval_range (object, &position, &position, soft);
-  if (NULL_INTERVAL_P (i))
+  if (!i)
     return limit;
 
   here_val = textget (i->plist, prop);
   next = next_interval (i);
-  while (! NULL_INTERVAL_P (next)
+  while (next
 	 && EQ (here_val, textget (next->plist, prop))
 	 && (NILP (limit) || next->position < XFASTINT (limit)))
     next = next_interval (next);
 
-  if (NULL_INTERVAL_P (next)
+  if (!next
       || (next->position
 	  >= (INTEGERP (limit)
 	      ? XFASTINT (limit)
@@ -1029,7 +1029,7 @@ back past position LIMIT; return LIMIT if nothing is found until LIMIT.  */)
     CHECK_NUMBER_COERCE_MARKER (limit);
 
   i = validate_interval_range (object, &position, &position, soft);
-  if (NULL_INTERVAL_P (i))
+  if (!i)
     return limit;
 
   /* Start with the interval containing the char before point.  */
@@ -1037,12 +1037,12 @@ back past position LIMIT; return LIMIT if nothing is found until LIMIT.  */)
     i = previous_interval (i);
 
   previous = previous_interval (i);
-  while (!NULL_INTERVAL_P (previous) && intervals_equal (previous, i)
+  while (previous && intervals_equal (previous, i)
 	 && (NILP (limit)
 	     || (previous->position + LENGTH (previous) > XFASTINT (limit))))
     previous = previous_interval (previous);
 
-  if (NULL_INTERVAL_P (previous)
+  if (!previous
       || (previous->position + LENGTH (previous)
 	  <= (INTEGERP (limit)
 	      ? XFASTINT (limit)
@@ -1080,21 +1080,21 @@ back past position LIMIT; return LIMIT if nothing is found until LIMIT.  */)
   i = validate_interval_range (object, &position, &position, soft);
 
   /* Start with the interval containing the char before point.  */
-  if (!NULL_INTERVAL_P (i) && i->position == XFASTINT (position))
+  if (i && i->position == XFASTINT (position))
     i = previous_interval (i);
 
-  if (NULL_INTERVAL_P (i))
+  if (!i)
     return limit;
 
   here_val = textget (i->plist, prop);
   previous = previous_interval (i);
-  while (!NULL_INTERVAL_P (previous)
+  while (previous
 	 && EQ (here_val, textget (previous->plist, prop))
 	 && (NILP (limit)
 	     || (previous->position + LENGTH (previous) > XFASTINT (limit))))
     previous = previous_interval (previous);
 
-  if (NULL_INTERVAL_P (previous)
+  if (!previous
       || (previous->position + LENGTH (previous)
 	  <= (INTEGERP (limit)
 	      ? XFASTINT (limit)
@@ -1130,7 +1130,7 @@ Return t if any property value actually changed, nil otherwise.  */)
     XSETBUFFER (object, current_buffer);
 
   i = validate_interval_range (object, &start, &end, hard);
-  if (NULL_INTERVAL_P (i))
+  if (!i)
     return Qnil;
 
   s = XINT (start);
@@ -1277,13 +1277,13 @@ set_text_properties (Lisp_Object start, Lisp_Object end, Lisp_Object properties,
       if (! STRING_INTERVALS (object))
 	return Qnil;
 
-      STRING_SET_INTERVALS (object, NULL_INTERVAL);
+      STRING_SET_INTERVALS (object, NULL);
       return Qt;
     }
 
   i = validate_interval_range (object, &start, &end, soft);
 
-  if (NULL_INTERVAL_P (i))
+  if (!i)
     {
       /* If buffer has no properties, and we want none, return now.  */
       if (NILP (properties))
@@ -1296,7 +1296,7 @@ set_text_properties (Lisp_Object start, Lisp_Object end, Lisp_Object properties,
 
       i = validate_interval_range (object, &start, &end, hard);
       /* This can return if start == end.  */
-      if (NULL_INTERVAL_P (i))
+      if (!i)
 	return Qnil;
     }
 
@@ -1321,7 +1321,7 @@ set_text_properties (Lisp_Object start, Lisp_Object end, Lisp_Object properties,
 void
 set_text_properties_1 (Lisp_Object start, Lisp_Object end, Lisp_Object properties, Lisp_Object buffer, INTERVAL i)
 {
-  register INTERVAL prev_changed = NULL_INTERVAL;
+  register INTERVAL prev_changed = NULL;
   register ptrdiff_t s, len;
   INTERVAL unchanged;
 
@@ -1378,7 +1378,7 @@ set_text_properties_1 (Lisp_Object start, Lisp_Object end, Lisp_Object propertie
 	     merge the intervals, so as to make the undo records
 	     and cause redisplay to happen.  */
 	  set_properties (properties, i, buffer);
-	  if (!NULL_INTERVAL_P (prev_changed))
+	  if (prev_changed)
 	    merge_interval_left (i);
 	  return;
 	}
@@ -1389,7 +1389,7 @@ set_text_properties_1 (Lisp_Object start, Lisp_Object end, Lisp_Object propertie
 	 merge the intervals, so as to make the undo records
 	 and cause redisplay to happen.  */
       set_properties (properties, i, buffer);
-      if (NULL_INTERVAL_P (prev_changed))
+      if (!prev_changed)
 	prev_changed = i;
       else
 	prev_changed = i = merge_interval_left (i);
@@ -1421,7 +1421,7 @@ Use `set-text-properties' if you want to remove all text properties.  */)
     XSETBUFFER (object, current_buffer);
 
   i = validate_interval_range (object, &start, &end, soft);
-  if (NULL_INTERVAL_P (i))
+  if (!i)
     return Qnil;
 
   s = XINT (start);
@@ -1508,7 +1508,7 @@ Return t if any property was actually removed, nil otherwise.  */)
     XSETBUFFER (object, current_buffer);
 
   i = validate_interval_range (object, &start, &end, soft);
-  if (NULL_INTERVAL_P (i))
+  if (!i)
     return Qnil;
 
   s = XINT (start);
@@ -1613,11 +1613,11 @@ markers).  If OBJECT is a string, START and END are 0-based indices into it.  */
   if (NILP (object))
     XSETBUFFER (object, current_buffer);
   i = validate_interval_range (object, &start, &end, soft);
-  if (NULL_INTERVAL_P (i))
+  if (!i)
     return (!NILP (value) || EQ (start, end) ? Qnil : start);
   e = XINT (end);
 
-  while (! NULL_INTERVAL_P (i))
+  while (i)
     {
       if (i->position >= e)
 	break;
@@ -1649,12 +1649,12 @@ markers).  If OBJECT is a string, START and END are 0-based indices into it.  */
   if (NILP (object))
     XSETBUFFER (object, current_buffer);
   i = validate_interval_range (object, &start, &end, soft);
-  if (NULL_INTERVAL_P (i))
+  if (!i)
     return (NILP (value) || EQ (start, end)) ? Qnil : start;
   s = XINT (start);
   e = XINT (end);
 
-  while (! NULL_INTERVAL_P (i))
+  while (i)
     {
       if (i->position >= e)
 	break;
@@ -1759,7 +1759,7 @@ copy_text_properties (Lisp_Object start, Lisp_Object end, Lisp_Object src, Lisp_
   struct gcpro gcpro1, gcpro2;
 
   i = validate_interval_range (src, &start, &end, soft);
-  if (NULL_INTERVAL_P (i))
+  if (!i)
     return Qnil;
 
   CHECK_NUMBER_COERCE_MARKER (pos);
@@ -1811,7 +1811,7 @@ copy_text_properties (Lisp_Object start, Lisp_Object end, Lisp_Object src, Lisp_
 	}
 
       i = next_interval (i);
-      if (NULL_INTERVAL_P (i))
+      if (!i)
 	break;
 
       p += len;
@@ -1852,7 +1852,7 @@ text_property_list (Lisp_Object object, Lisp_Object start, Lisp_Object end, Lisp
   result = Qnil;
 
   i = validate_interval_range (object, &start, &end, soft);
-  if (!NULL_INTERVAL_P (i))
+  if (i)
     {
       ptrdiff_t s = XINT (start);
       ptrdiff_t e = XINT (end);
@@ -1884,7 +1884,7 @@ text_property_list (Lisp_Object object, Lisp_Object start, Lisp_Object end, Lisp
 			    result);
 
 	  i = next_interval (i);
-	  if (NULL_INTERVAL_P (i))
+	  if (!i)
 	    break;
 	  s = i->position;
 	}
@@ -2007,7 +2007,7 @@ verify_interval_modification (struct buffer *buf,
   interval_insert_behind_hooks = Qnil;
   interval_insert_in_front_hooks = Qnil;
 
-  if (NULL_INTERVAL_P (intervals))
+  if (!intervals)
     return;
 
   if (start > end)
@@ -2048,7 +2048,7 @@ verify_interval_modification (struct buffer *buf,
 	     indirectly defined via the category property.  */
 	  if (i != prev)
 	    {
-	      if (! NULL_INTERVAL_P (i))
+	      if (i)
 		{
 		  after = textget (i->plist, Qread_only);
 
@@ -2068,7 +2068,7 @@ verify_interval_modification (struct buffer *buf,
 		    }
 		}
 
-	      if (! NULL_INTERVAL_P (prev))
+	      if (prev)
 		{
 		  before = textget (prev->plist, Qread_only);
 
@@ -2088,7 +2088,7 @@ verify_interval_modification (struct buffer *buf,
 		    }
 		}
 	    }
-	  else if (! NULL_INTERVAL_P (i))
+	  else if (i)
 	    {
 	      after = textget (i->plist, Qread_only);
 
@@ -2115,10 +2115,10 @@ verify_interval_modification (struct buffer *buf,
 	}
 
       /* Run both insert hooks (just once if they're the same).  */
-      if (!NULL_INTERVAL_P (prev))
+      if (prev)
 	interval_insert_behind_hooks
 	  = textget (prev->plist, Qinsert_behind_hooks);
-      if (!NULL_INTERVAL_P (i))
+      if (i)
 	interval_insert_in_front_hooks
 	  = textget (i->plist, Qinsert_in_front_hooks);
     }
@@ -2146,7 +2146,7 @@ verify_interval_modification (struct buffer *buf,
 	  i = next_interval (i);
 	}
       /* Keep going thru the interval containing the char before END.  */
-      while (! NULL_INTERVAL_P (i) && i->position < end);
+      while (i && i->position < end);
 
       if (!inhibit_modification_hooks)
 	{
diff --git a/src/xdisp.c b/src/xdisp.c
index 73dc272e5e2..a2fc4f61669 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -3321,7 +3321,7 @@ compute_stop_pos (struct it *it)
      interval if there isn't such an interval.  */
   position = make_number (charpos);
   iv = validate_interval_range (object, &position, &position, 0);
-  if (!NULL_INTERVAL_P (iv))
+  if (iv)
     {
       Lisp_Object values_here[LAST_PROP_IDX];
       struct props *p;
@@ -3333,7 +3333,7 @@ compute_stop_pos (struct it *it)
       /* Look for an interval following iv that has different
 	 properties.  */
       for (next_iv = next_interval (iv);
-	   (!NULL_INTERVAL_P (next_iv)
+	   (next_iv
 	    && (NILP (limit)
 		|| XFASTINT (limit) > next_iv->position));
 	   next_iv = next_interval (next_iv))
@@ -3351,7 +3351,7 @@ compute_stop_pos (struct it *it)
 	    break;
 	}
 
-      if (!NULL_INTERVAL_P (next_iv))
+      if (next_iv)
 	{
 	  if (INTEGERP (limit)
 	      && next_iv->position >= XFASTINT (limit))