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+/****************************************************************************
+ * Copyright (c) 1998-2007,2008 Free Software Foundation, Inc.              *
+ *                                                                          *
+ * Permission is hereby granted, free of charge, to any person obtaining a  *
+ * copy of this software and associated documentation files (the            *
+ * "Software"), to deal in the Software without restriction, including      *
+ * without limitation the rights to use, copy, modify, merge, publish,      *
+ * distribute, distribute with modifications, sublicense, and/or sell       *
+ * copies of the Software, and to permit persons to whom the Software is    *
+ * furnished to do so, subject to the following conditions:                 *
+ *                                                                          *
+ * The above copyright notice and this permission notice shall be included  *
+ * in all copies or substantial portions of the Software.                   *
+ *                                                                          *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS  *
+ * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF               *
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.   *
+ * IN NO EVENT SHALL THE ABOVE COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,   *
+ * DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR    *
+ * OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR    *
+ * THE USE OR OTHER DEALINGS IN THE SOFTWARE.                               *
+ *                                                                          *
+ * Except as contained in this notice, the name(s) of the above copyright   *
+ * holders shall not be used in advertising or otherwise to promote the     *
+ * sale, use or other dealings in this Software without prior written       *
+ * authorization.                                                           *
+ ****************************************************************************/
+
+/****************************************************************************
+ *  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 1.42 2008/08/03 23:49:30 tom 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) strcpy(buf, "virt");
+	for (n = 0; n < screen_lines; n++)
+	    (void) sprintf(buf + 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;
+
+#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(line, " ");
+	do {
+	    oldnums[n++] = atoi(st);
+	} while
+	    ((st = strtok((char *) NULL, " ")) != 0);
+
+	/* display it */
+	(void) fputs("Initial input:\n", stderr);
+	_nc_linedump();
+
+	_nc_scroll_optimize();
+    }
+}
+
+#endif /* SCROLLDEBUG */
+
+/* hardscroll.c ends here */