GNU Emac's buffer data management

emacs_insert.c

void
insert_1_both (const char *string,
		   ptrdiff_t nchars, ptrdiff_t nbytes,
		   bool inherit, bool prepare, bool before_markers)
{
  if (nchars == 0)
	return;

  if (NILP (BVAR (current_buffer, enable_multibyte_characters)))
	nchars = nbytes;

  if (prepare)
	/* Do this before moving and increasing the gap,
	   because the before-change hooks might move the gap
	   or make it smaller.  */
	prepare_to_modify_buffer (PT, PT, NULL);

  if (PT != GPT)
	move_gap_both (PT, PT_BYTE);
  if (GAP_SIZE < nbytes)
	make_gap (nbytes - GAP_SIZE);

#ifdef BYTE_COMBINING_DEBUG
  if (count_combining_before (string, nbytes, PT, PT_BYTE)
	  || count_combining_after (string, nbytes, PT, PT_BYTE))
	emacs_abort ();
#endif

  /* Record deletion of the surrounding text that combines with
	 the insertion.  This, together with recording the insertion,
	 will add up to the right stuff in the undo list.  */
  record_insert (PT, nchars);
  MODIFF++;
  CHARS_MODIFF = MODIFF;

  memcpy (GPT_ADDR, string, nbytes);

  GAP_SIZE -= nbytes;
  GPT += nchars;
  ZV += nchars;
  Z += nchars;
  GPT_BYTE += nbytes;
  ZV_BYTE += nbytes;
  Z_BYTE += nbytes;
  if (GAP_SIZE > 0) *(GPT_ADDR) = 0; /* Put an anchor.  */

  eassert (GPT <= GPT_BYTE);

  /* The insert may have been in the unchanged region, so check again.  */
  if (Z - GPT < END_UNCHANGED)
	END_UNCHANGED = Z - GPT;

  adjust_overlays_for_insert (PT, nchars);
  adjust_markers_for_insert (PT, PT_BYTE,
				 PT + nchars, PT_BYTE + nbytes,
				 before_markers);

  offset_intervals (current_buffer, PT, nchars);

  if (!inherit && buffer_intervals (current_buffer))
	set_text_properties (make_number (PT), make_number (PT + nchars),
			 Qnil, Qnil, Qnil);

  adjust_point (nchars, nbytes);

  check_markers ();
}