text: /*	$OpenBSD: hardscroll.c,v 1.7 2010/01/12 23:22:07 nicm Exp $	*/
  
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  /****************************************************************************
   *  Author: Zeyd M. Ben-Halim <zmbenhal@netcom.com> 1992,1995               *
   *     and: Eric S. Raymond <esr@snark.thyrsus.com>                         *
   *     and: Thomas E. Dickey                        1996-on                 *
   *     and: Alexander V Lukyanov                    1997-1998               *
   ****************************************************************************/
  
  /******************************************************************************
  
  NAME
     hardscroll.c -- hardware-scrolling optimization for ncurses
  
  SYNOPSIS
     void _nc_scroll_optimize(void)
  
  DESCRIPTION
  			OVERVIEW
  
  This algorithm for computes optimum hardware scrolling to transform an
  old screen (curscr) into a new screen (newscr) via vertical line moves.
  
  Because the screen has a `grain' (there are insert/delete/scroll line
  operations but no insert/delete/scroll column operations), it is efficient
  break the update algorithm into two pieces: a first stage that does only line
  moves, optimizing the end product of user-invoked insertions, deletions, and
  scrolls; and a second phase (corresponding to the present doupdate code in
  ncurses) that does only line transformations.
  
  The common case we want hardware scrolling for is to handle line insertions
  and deletions in screen-oriented text-editors.  This two-stage approach will
  accomplish that at a low computation and code-size cost.
  
  			LINE-MOVE COMPUTATION
  
  Now, to a discussion of the line-move computation.
  
  For expository purposes, consider the screen lines to be represented by
  integers 0..23 (with the understanding that the value of 23 may vary).
  Let a new line introduced by insertion, scrolling, or at the bottom of
  the screen following a line delete be given the index -1.
  
  Assume that the real screen starts with lines 0..23.  Now, we have
  the following possible line-oriented operations on the screen:
  
  Insertion: inserts a line at a given screen row, forcing all lines below
  to scroll forward.  The last screen line is lost.  For example, an insertion
  at line 5 would produce: 0..4 -1 5..23.
  
  Deletion: deletes a line at a given screen row, forcing all lines below
  to scroll forward.  The last screen line is made new.  For example, a deletion
  at line 7 would produce: 0..6 8..23 -1.
  
  Scroll up: move a range of lines up 1.  The bottom line of the range
  becomes new.  For example, scrolling up the region from 9 to 14 will
  produce 0..8 10..14 -1 15..23.
  
  Scroll down: move a range of lines down 1.  The top line of the range
  becomes new.  For example, scrolling down the region from 12 to 16 will produce
  0..11 -1 12..15 17..23.
  
  Now, an obvious property of all these operations is that they preserve the
  order of old lines, though not their position in the sequence.
  
  The key trick of this algorithm is that the original line indices described
  above are actually maintained as _line[].oldindex fields in the window
  structure, and stick to each line through scroll and insert/delete operations.
  
  Thus, it is possible at update time to look at the oldnum fields and compute
  an optimal set of il/dl/scroll operations that will take the real screen
  lines to the virtual screen lines.  Once these vertical moves have been done,
  we can hand off to the second stage of the update algorithm, which does line
  transformations.
  
  Note that the move computation does not need to have the full generality
  of a diff algorithm (which it superficially resembles) because lines cannot
  be moved out of order.
  
  			THE ALGORITHM
  
  The scrolling is done in two passes. The first pass is from top to bottom
  scroling hunks UP. The second one is from bottom to top scrolling hunks DOWN.
  Obviously enough, no lines to be scrolled will be destroyed. (lav)
  
  HOW TO TEST THIS:
  
  Use the following production:
  
  hardscroll: hardscroll.c
  	$(CC) -g -DSCROLLDEBUG hardscroll.c -o hardscroll
  
  Then just type scramble vectors and watch.  The following test loads are
  a representative sample of cases:
  
  -----------------------------  CUT HERE ------------------------------------
  # No lines moved
   0  1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
  #
  # A scroll up
   1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 -1
  #
  # A scroll down
  -1  0  1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16 17 18 19 20 21 22
  #
  # An insertion (after line 12)
   0  1  2  3  4  5  6  7  8  9 10 11 12 -1 13 14 15 16 17 18 19 20 21 22
  #
  # A simple deletion (line 10)
   0  1  2  3  4  5  6  7  8  9  11 12 13 14 15 16 17 18 19 20 21 22 23 -1
  #
  # A more complex case
  -1 -1 -1 -1 -1  3  4  5  6  7  -1 -1  8  9 10 11 12 13 14 15 16 17 -1 -1
  -----------------------------  CUT HERE ------------------------------------
  
  AUTHOR
      Eric S. Raymond <esr@snark.thyrsus.com>, November 1994
      New algorithm by Alexander V. Lukyanov <lav@yars.free.net>, Aug 1997
  
  *****************************************************************************/
  
  #include <curses.priv.h>
  
  MODULE_ID("$Id: hardscroll.c,v 1.7 2010/01/12 23:22:07 nicm Exp $")
  
  #if defined(SCROLLDEBUG) || defined(HASHDEBUG)
  
  # undef screen_lines
  # define screen_lines MAXLINES
  NCURSES_EXPORT_VAR(int)
  oldnums[MAXLINES];
  # define OLDNUM(n)	oldnums[n]
  # define _tracef	printf
  # undef TR
  # define TR(n, a)	if (_nc_tracing & (n)) { _tracef a ; putchar('\n'); }
  
  extern NCURSES_EXPORT_VAR(unsigned) _nc_tracing;
  
  #else /* no debug */
  
  /* OLDNUM(n) indicates which line will be shifted to the position n.
     if OLDNUM(n) == _NEWINDEX, then the line n in new, not shifted from
     somewhere. */
  NCURSES_EXPORT_VAR(int *)
  _nc_oldnums = 0;		/* obsolete: keep for ABI compat */
  
  # if USE_HASHMAP
  #  define oldnums       SP->_oldnum_list
  #  define OLDNUM(n)	oldnums[n]
  # else				/* !USE_HASHMAP */
  #  define OLDNUM(n)	newscr->_line[n].oldindex
  # endif				/* !USE_HASHMAP */
  
  #define OLDNUM_SIZE     SP->_oldnum_size
  
  #endif /* defined(SCROLLDEBUG) || defined(HASHDEBUG) */
  
  NCURSES_EXPORT(void)
  _nc_scroll_optimize(void)
  /* scroll optimization to transform curscr to newscr */
  {
      int i;
      int start, end, shift;
  
      TR(TRACE_ICALLS, (T_CALLED("_nc_scroll_optimize")));
  
  #if !defined(SCROLLDEBUG) && !defined(HASHDEBUG)
  #if USE_HASHMAP
      /* get enough storage */
      if (OLDNUM_SIZE < screen_lines) {
  	int *new_oldnums = typeRealloc(int, screen_lines, oldnums);
  	if (!new_oldnums)
  	    return;
  	oldnums = new_oldnums;
  	OLDNUM_SIZE = screen_lines;
      }
      /* calculate the indices */
      _nc_hash_map();
  #endif
  #endif /* !defined(SCROLLDEBUG) && !defined(HASHDEBUG) */
  
  #ifdef TRACE
      if (USE_TRACEF(TRACE_UPDATE | TRACE_MOVE)) {
  	_nc_linedump();
  	_nc_unlock_global(tracef);
      }
  #endif /* TRACE */
  
      /* pass 1 - from top to bottom scrolling up */
      for (i = 0; i < screen_lines;) {
  	while (i < screen_lines && (OLDNUM(i) == _NEWINDEX || OLDNUM(i) <= i))
  	    i++;
  	if (i >= screen_lines)
  	    break;
  
  	shift = OLDNUM(i) - i;	/* shift > 0 */
  	start = i;
  
  	i++;
  	while (i < screen_lines && OLDNUM(i) != _NEWINDEX && OLDNUM(i) - i
  	       == shift)
  	    i++;
  	end = i - 1 + shift;
  
  	TR(TRACE_UPDATE | TRACE_MOVE, ("scroll [%d, %d] by %d", start, end, shift));
  #if !defined(SCROLLDEBUG) && !defined(HASHDEBUG)
  	if (_nc_scrolln(shift, start, end, screen_lines - 1) == ERR) {
  	    TR(TRACE_UPDATE | TRACE_MOVE, ("unable to scroll"));
  	    continue;
  	}
  #endif /* !defined(SCROLLDEBUG) && !defined(HASHDEBUG) */
      }
  
      /* pass 2 - from bottom to top scrolling down */
      for (i = screen_lines - 1; i >= 0;) {
  	while (i >= 0 && (OLDNUM(i) == _NEWINDEX || OLDNUM(i) >= i))
  	    i--;
  	if (i < 0)
  	    break;
  
  	shift = OLDNUM(i) - i;	/* shift < 0 */
  	end = i;
  
  	i--;
  	while (i >= 0 && OLDNUM(i) != _NEWINDEX && OLDNUM(i) - i == shift)
  	    i--;
  	start = i + 1 - (-shift);
  
  	TR(TRACE_UPDATE | TRACE_MOVE, ("scroll [%d, %d] by %d", start, end, shift));
  #if !defined(SCROLLDEBUG) && !defined(HASHDEBUG)
  	if (_nc_scrolln(shift, start, end, screen_lines - 1) == ERR) {
  	    TR(TRACE_UPDATE | TRACE_MOVE, ("unable to scroll"));
  	    continue;
  	}
  #endif /* !defined(SCROLLDEBUG) && !defined(HASHDEBUG) */
      }
      TR(TRACE_ICALLS, (T_RETURN("")));
  }
  
  #if defined(TRACE) || defined(SCROLLDEBUG) || defined(HASHDEBUG)
  NCURSES_EXPORT(void)
  _nc_linedump(void)
  /* dump the state of the real and virtual oldnum fields */
  {
      int n;
      char *buf = 0;
      size_t want = (screen_lines + 1) * 4;
  
      if ((buf = typeMalloc(char, want)) != 0) {
  
  	(void) strlcpy(buf, "virt", want);
  	for (n = 0; n < screen_lines; n++)
  		(void) snprintf(buf + strlen(buf), want - strlen(buf), " %02d", OLDNUM(n));
  	TR(TRACE_UPDATE | TRACE_MOVE, (buf));
  	free(buf);
      }
  }
  #endif /* defined(TRACE) || defined(SCROLLDEBUG) */
  
  #ifdef SCROLLDEBUG
  
  int
  main(int argc GCC_UNUSED, char *argv[]GCC_UNUSED)
  {
      char line[BUFSIZ], *st, *last;
  
  #ifdef TRACE
      _nc_tracing = TRACE_MOVE;
  #endif
      for (;;) {
  	int n;
  
  	for (n = 0; n < screen_lines; n++)
  	    oldnums[n] = _NEWINDEX;
  
  	/* grab the test vector */
  	if (fgets(line, sizeof(line), stdin) == (char *) NULL)
  	    exit(EXIT_SUCCESS);
  
  	/* parse it */
  	n = 0;
  	if (line[0] == '#') {
  	    (void) fputs(line, stderr);
  	    continue;
  	}
  	st = strtok_r(line, " ", &last);
  	do {
  	    oldnums[n++] = atoi(st);
  	} while
  	    ((st = strtok_r((char *) NULL, " ", &last)) != 0);
  
  	/* display it */
  	(void) fputs("Initial input:\n", stderr);
  	_nc_linedump();
  
  	_nc_scroll_optimize();
      }
  }
  
  #endif /* SCROLLDEBUG */
  
  /* hardscroll.c ends here */
  