Avoid unwanted point motion in Fline_beginning_position.

* lisp.h (scan_newline_from_point): Add prototype.
* search.c (scan_newline_from_point): New function, refactored from...
* cmds.c (Fforward_line): ...adjusted user.
* editfns.c (Fline_beginning_position): Use scan_newline_from_point
and simplify the former since the latter doesn't move point.

src/ChangeLog

+2014-10-15  Dmitry Antipov  <dmantipov@yandex.ru>
+
+	Avoid unwanted point motion in Fline_beginning_position.
+	* lisp.h (scan_newline_from_point): Add prototype.
+	* search.c (scan_newline_from_point): New function, refactored from...
+	* cmds.c (Fforward_line): ...adjusted user.
+	* editfns.c (Fline_beginning_position): Use scan_newline_from_point
+	and simplify the former since the latter doesn't move point.
+
 2014-10-14  Dmitry Antipov  <dmantipov@yandex.ru>
 
 	Cleanup terminal handling code.

src/cmds.c

@@ -131,12 +131,7 @@ successfully moved (for the return value).  */)
       count = XINT (n);
     }
 
-  if (count <= 0)
-    pos = find_newline (PT, PT_BYTE, BEGV, BEGV_BYTE, count - 1,
-			&shortage, &pos_byte, 1);
-  else
-    pos = find_newline (PT, PT_BYTE, ZV, ZV_BYTE, count,
-			&shortage, &pos_byte, 1);
+  shortage = scan_newline_from_point (count, &pos, &pos_byte);
 
   SET_PT_BOTH (pos, pos_byte);
 

src/editfns.c

@@ -787,26 +787,17 @@ boundaries, bind `inhibit-field-text-motion' to t.
 This function does not move point.  */)
   (Lisp_Object n)
 {
-  ptrdiff_t orig, orig_byte, end;
-  ptrdiff_t count = SPECPDL_INDEX ();
-  specbind (Qinhibit_point_motion_hooks, Qt);
+  ptrdiff_t charpos, bytepos;
 
   if (NILP (n))
     XSETFASTINT (n, 1);
   else
     CHECK_NUMBER (n);
 
-  orig = PT;
-  orig_byte = PT_BYTE;
-  Fforward_line (make_number (XINT (n) - 1));
-  end = PT;
-
-  SET_PT_BOTH (orig, orig_byte);
-
-  unbind_to (count, Qnil);
+  scan_newline_from_point (XINT (n) - 1, &charpos, &bytepos);
 
   /* Return END constrained to the current input field.  */
-  return Fconstrain_to_field (make_number (end), make_number (orig),
+  return Fconstrain_to_field (make_number (charpos), make_number (PT),
 			      XINT (n) != 1 ? Qt : Qnil,
 			      Qt, Qnil);
 }

src/lisp.h

@@ -4066,6 +4066,7 @@ extern ptrdiff_t find_newline (ptrdiff_t, ptrdiff_t, ptrdiff_t, ptrdiff_t,
 			       ptrdiff_t, ptrdiff_t *, ptrdiff_t *, bool);
 extern ptrdiff_t scan_newline (ptrdiff_t, ptrdiff_t, ptrdiff_t, ptrdiff_t,
 			       ptrdiff_t, bool);
+extern ptrdiff_t scan_newline_from_point (ptrdiff_t, ptrdiff_t *, ptrdiff_t *);
 extern ptrdiff_t find_newline_no_quit (ptrdiff_t, ptrdiff_t,
 				       ptrdiff_t, ptrdiff_t *);
 extern ptrdiff_t find_before_next_newline (ptrdiff_t, ptrdiff_t,

src/search.c

@@ -985,6 +985,24 @@ scan_newline (ptrdiff_t start, ptrdiff_t start_byte,
   return shortage;
 }
 
+/* Like above, but always scan from point and report the
+   resulting position in *CHARPOS and *BYTEPOS.  */
+
+ptrdiff_t
+scan_newline_from_point (ptrdiff_t count, ptrdiff_t *charpos,
+			 ptrdiff_t *bytepos)
+{
+  ptrdiff_t shortage;
+
+  if (count <= 0)
+    *charpos = find_newline (PT, PT_BYTE, BEGV, BEGV_BYTE, count - 1,
+			     &shortage, bytepos, 1);
+  else
+    *charpos = find_newline (PT, PT_BYTE, ZV, ZV_BYTE, count,
+			     &shortage, bytepos, 1);
+  return shortage;
+}
+
 /* Like find_newline, but doesn't allow QUITting and doesn't return
    SHORTAGE.  */
 ptrdiff_t