Style of comments corrected.

(interval_of): New function.

src/textprop.c

 /* Interface code for dealing with text properties.
-   Copyright (C) 1993, 1994, 1995 Free Software Foundation, Inc.
+   Copyright (C) 1993, 1994, 1995, 1997 Free Software Foundation, Inc.
 
 This file is part of GNU Emacs.
 
@@ -44,12 +44,12 @@ Boston, MA 02111-1307, USA.  */
   only once on the list.  Although some code i.e., remove_properties,
   handles the more general case, the uniqueness of properties is
   necessary for the system to remain consistent.  This requirement
-  is enforced by the subrs installing properties onto the intervals. */
+  is enforced by the subrs installing properties onto the intervals.  */
 
 /* The rest of the file is within this conditional */
 #ifdef USE_TEXT_PROPERTIES
 
-/* Types of hooks. */
+/* Types of hooks.  */
 Lisp_Object Qmouse_left;
 Lisp_Object Qmouse_entered;
 Lisp_Object Qpoint_left;
@@ -57,7 +57,7 @@ Lisp_Object Qpoint_entered;
 Lisp_Object Qcategory;
 Lisp_Object Qlocal_map;
 
-/* Visual properties text (including strings) may have. */
+/* Visual properties text (including strings) may have.  */
 Lisp_Object Qforeground, Qbackground, Qfont, Qunderline, Qstipple;
 Lisp_Object Qinvisible, Qread_only, Qintangible;
 
@@ -116,7 +116,7 @@ validate_interval_range (object, begin, end, force)
   CHECK_NUMBER_COERCE_MARKER (*end, 0);
 
   /* If we are asked for a point, but from a subr which operates
-     on a range, then return nothing. */
+     on a range, then return nothing.  */
   if (EQ (*begin, *end) && begin != end)
     return NULL_INTERVAL;
 
@@ -137,7 +137,7 @@ validate_interval_range (object, begin, end, force)
 	args_out_of_range (*begin, *end);
       i = BUF_INTERVALS (b);
 
-      /* If there's no text, there are no properties. */
+      /* If there's no text, there are no properties.  */
       if (BUF_BEGV (b) == BUF_ZV (b))
 	return NULL_INTERVAL;
 
@@ -171,7 +171,7 @@ validate_interval_range (object, begin, end, force)
 
 /* Validate LIST as a property list.  If LIST is not a list, then
    make one consisting of (LIST nil).  Otherwise, verify that LIST
-   is even numbered and thus suitable as a plist. */
+   is even numbered and thus suitable as a plist.  */
 
 static Lisp_Object
 validate_plist (list)
@@ -198,7 +198,7 @@ validate_plist (list)
 }
 
 /* Return nonzero if interval I has all the properties,
-   with the same values, of list PLIST. */
+   with the same values, of list PLIST.  */
 
 static int
 interval_has_all_properties (plist, i)
@@ -208,7 +208,7 @@ interval_has_all_properties (plist, i)
   register Lisp_Object tail1, tail2, sym1, sym2;
   register int found;
 
-  /* Go through each element of PLIST. */
+  /* Go through each element of PLIST.  */
   for (tail1 = plist; ! NILP (tail1); tail1 = Fcdr (Fcdr (tail1)))
     {
       sym1 = Fcar (tail1);
@@ -219,11 +219,11 @@ interval_has_all_properties (plist, i)
 	if (EQ (sym1, Fcar (tail2)))
 	  {
 	    /* Found the same property on both lists.  If the
-	       values are unequal, return zero. */
+	       values are unequal, return zero.  */
 	    if (! EQ (Fcar (Fcdr (tail1)), Fcar (Fcdr (tail2))))
 	      return 0;
 
-	    /* Property has same value on both lists;  go to next one. */
+	    /* Property has same value on both lists;  go to next one.  */
 	    found = 1;
 	    break;
 	  }
@@ -236,7 +236,7 @@ interval_has_all_properties (plist, i)
 }
 
 /* Return nonzero if the plist of interval I has any of the
-   properties of PLIST, regardless of their values. */
+   properties of PLIST, regardless of their values.  */
 
 static INLINE int
 interval_has_some_properties (plist, i)
@@ -245,7 +245,7 @@ interval_has_some_properties (plist, i)
 {
   register Lisp_Object tail1, tail2, sym;
 
-  /* Go through each element of PLIST. */
+  /* Go through each element of PLIST.  */
   for (tail1 = plist; ! NILP (tail1); tail1 = Fcdr (Fcdr (tail1)))
     {
       sym = Fcar (tail1);
@@ -349,7 +349,7 @@ add_properties (plist, i, object)
      I and its plist are also protected, via OBJECT.  */
   GCPRO3 (tail1, sym1, val1);
 
-  /* Go through each element of PLIST. */
+  /* Go through each element of PLIST.  */
   for (tail1 = plist; ! NILP (tail1); tail1 = Fcdr (Fcdr (tail1)))
     {
       sym1 = Fcar (tail1);
@@ -365,11 +365,11 @@ add_properties (plist, i, object)
 	    register Lisp_Object this_cdr;
 
 	    this_cdr = Fcdr (tail2);
-	    /* Found the property.  Now check its value. */
+	    /* Found the property.  Now check its value.  */
 	    found = 1;
 
 	    /* The properties have the same value on both lists.
-	       Continue to the next property. */
+	       Continue to the next property.  */
 	    if (EQ (val1, Fcar (this_cdr)))
 	      break;
 
@@ -418,7 +418,7 @@ remove_properties (plist, i, object)
   register int changed = 0;
 
   current_plist = i->plist;
-  /* Go through each element of plist. */
+  /* Go through each element of plist.  */
   for (tail1 = plist; ! NILP (tail1); tail1 = Fcdr (Fcdr (tail1)))
     {
       sym = Fcar (tail1);
@@ -465,7 +465,7 @@ remove_properties (plist, i, object)
 
 #if 0
 /* Remove all properties from interval I.  Return non-zero
-   if this changes the interval. */
+   if this changes the interval.  */
 
 static INLINE int
 erase_properties (i)
@@ -479,6 +479,48 @@ erase_properties (i)
 }
 #endif
 
+/* Returns the interval of the POSITION in OBJECT. 
+   POSITION is BEG-based.  */
+
+INTERVAL
+interval_of (position, object)
+     int position;
+     Lisp_Object object;
+{
+  register INTERVAL i;
+  int beg, end;
+
+  if (NILP (object))
+    XSETBUFFER (object, current_buffer);
+
+  CHECK_STRING_OR_BUFFER (object, 0);
+
+  if (BUFFERP (object))
+    {
+      register struct buffer *b = XBUFFER (object);
+
+      beg = BUF_BEGV (b);
+      end = BUF_ZV (b);
+      i = BUF_INTERVALS (b);
+    }
+  else
+    {
+      register struct Lisp_String *s = XSTRING (object);
+
+      /* We expect position to be 1-based.  */
+      beg = BEG;
+      end = s->size + BEG;
+      i = s->intervals;
+    }
+
+  if (!(beg <= position && position <= end))
+    args_out_of_range (position, position);
+  if (beg == end || NULL_INTERVAL_P (i))
+    return NULL_INTERVAL;
+    
+  return find_interval (i, position);
+}
+
 DEFUN ("text-properties-at", Ftext_properties_at,
        Stext_properties_at, 1, 2, 0,
   "Return the list of properties held by the character at POSITION\n\
@@ -900,11 +942,11 @@ Return t if any property value actually changed, nil otherwise.")
   GCPRO1 (properties);
 
   /* If we're not starting on an interval boundary, we have to
-    split this interval. */
+    split this interval.  */
   if (i->position != s)
     {
       /* If this interval already has the properties, we can
-         skip it. */
+         skip it.  */
       if (interval_has_all_properties (properties, i))
 	{
 	  int got = (LENGTH (i) - (s - i->position));
@@ -1155,7 +1197,7 @@ Return t if any property was actually removed, nil otherwise.")
   if (i->position != s)
     {
       /* No properties on this first interval -- return if
-         it covers the entire region. */
+         it covers the entire region.  */
       if (! interval_has_some_properties (properties, i))
 	{
 	  int got = (LENGTH (i) - (s - i->position));
@@ -1315,7 +1357,7 @@ is the string or buffer containing the text.")
       register int got;
       register INTERVAL unchanged = i;
 
-      /* If there are properties here, then this text will be modified. */
+      /* If there are properties here, then this text will be modified.  */
       if (! NILP (i->plist))
 	{
 	  i = split_interval_right (unchanged, s - unchanged->position);
@@ -1340,7 +1382,7 @@ is the string or buffer containing the text.")
       else if (LENGTH (i) - (s - i->position) <= len)
 	return Qnil;
       /* The amount of text to change extends past I, so just note
-	 how much we've gotten. */
+	 how much we've gotten.  */
       else
 	got = LENGTH (i) - (s - i->position);
 
@@ -1349,7 +1391,7 @@ is the string or buffer containing the text.")
       i = next_interval (i);
     }
 
-  /* We are starting at the beginning of an interval, I. */
+  /* We are starting at the beginning of an interval, I.  */
   while (len > 0)
     {
       if (LENGTH (i) >= len)
@@ -1383,7 +1425,7 @@ is the string or buffer containing the text.")
       else
 	{
 	  modified += ! NILP (i->plist);
-	  /* Merging I will give it the properties of PREV_CHANGED. */
+	  /* Merging I will give it the properties of PREV_CHANGED.  */
 	  prev_changed = i = merge_interval_left (i);
 	}
 
@@ -1463,7 +1505,7 @@ copy_text_properties (start, end, src, pos, dest, prop)
       if (! NILP (plist))
 	{
 	  /* Must defer modifications to the interval tree in case src
-	     and dest refer to the same string or buffer. */
+	     and dest refer to the same string or buffer.  */
 	  stuff = Fcons (Fcons (make_number (p),
 				Fcons (make_number (p + len),
 				       Fcons (plist, Qnil))),
@@ -1572,7 +1614,7 @@ verify_interval_modification (buf, start, end)
       if (NILP (Vinhibit_read_only) || CONSP (Vinhibit_read_only))
 	{
 	  /* If I and PREV differ we need to check for the read-only
-	     property together with its stickiness. If either I or
+	     property together with its stickiness.  If either I or
 	     PREV are 0, this check is all we need.
 	     We have to take special care, since read-only may be
 	     indirectly defined via the category property.  */