1 files changed, 139 insertions, 0 deletions
diff --git a/contrib/nvi/vi/v_undo.c b/contrib/nvi/vi/v_undo.c
new file mode 100644
index 0000000..d04a8a1
--- /dev/null
+++ b/contrib/nvi/vi/v_undo.c
@@ -0,0 +1,139 @@
+/*-
+ * Copyright (c) 1992, 1993, 1994
+ *	The Regents of the University of California.  All rights reserved.
+ * Copyright (c) 1992, 1993, 1994, 1995, 1996
+ *	Keith Bostic.  All rights reserved.
+ *
+ * See the LICENSE file for redistribution information.
+ */
+
+#include "config.h"
+
+#ifndef lint
+static const char sccsid[] = "@(#)v_undo.c	10.5 (Berkeley) 3/6/96";
+#endif /* not lint */
+
+#include <sys/types.h>
+#include <sys/queue.h>
+#include <sys/time.h>
+
+#include <bitstring.h>
+#include <errno.h>
+#include <limits.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include "../common/common.h"
+#include "vi.h"
+
+/*
+ * v_Undo -- U
+ *	Undo changes to this line.
+ *
+ * PUBLIC: int v_Undo __P((SCR *, VICMD *));
+ */
+int
+v_Undo(sp, vp)
+	SCR *sp;
+	VICMD *vp;
+{
+	/*
+	 * Historically, U reset the cursor to the first column in the line
+	 * (not the first non-blank).  This seems a bit non-intuitive, but,
+	 * considering that we may have undone multiple changes, anything
+	 * else (including the cursor position stored in the logging records)
+	 * is going to appear random.
+	 */
+	vp->m_final.cno = 0;
+
+	/*
+	 * !!!
+	 * Set up the flags so that an immediately subsequent 'u' will roll
+	 * forward, instead of backward.  In historic vi, a 'u' following a
+	 * 'U' redid all of the changes to the line.  Given that the user has
+	 * explicitly discarded those changes by entering 'U', it seems likely
+	 * that the user wants something between the original and end forms of
+	 * the line, so starting to replay the changes seems the best way to
+	 * get to there.
+	 */
+	F_SET(sp->ep, F_UNDO);
+	sp->ep->lundo = BACKWARD;
+
+	return (log_setline(sp));
+}
+
+/*
+ * v_undo -- u
+ *	Undo the last change.
+ *
+ * PUBLIC: int v_undo __P((SCR *, VICMD *));
+ */
+int
+v_undo(sp, vp)
+	SCR *sp;
+	VICMD *vp;
+{
+	EXF *ep;
+
+	/* Set the command count. */
+	VIP(sp)->u_ccnt = sp->ccnt;
+
+	/*
+	 * !!!
+	 * In historic vi, 'u' toggled between "undo" and "redo", i.e. 'u'
+	 * undid the last undo.  However, if there has been a change since
+	 * the last undo/redo, we always do an undo.  To make this work when
+	 * the user can undo multiple operations, we leave the old semantic
+	 * unchanged, but make '.' after a 'u' do another undo/redo operation.
+	 * This has two problems.
+	 *
+	 * The first is that 'u' didn't set '.' in historic vi.  So, if a
+	 * user made a change, realized it was in the wrong place, does a
+	 * 'u' to undo it, moves to the right place and then does '.', the
+	 * change was reapplied.  To make this work, we only apply the '.'
+	 * to the undo command if it's the command immediately following an
+	 * undo command.  See vi/vi.c:getcmd() for the details.
+	 *
+	 * The second is that the traditional way to view the numbered cut
+	 * buffers in vi was to enter the commands "1pu.u.u.u. which will
+	 * no longer work because the '.' immediately follows the 'u' command.
+	 * Since we provide a much better method of viewing buffers, and
+	 * nobody can think of a better way of adding in multiple undo, this
+	 * remains broken.
+	 *
+	 * !!!
+	 * There is change to historic practice for the final cursor position
+	 * in this implementation.  In historic vi, if an undo was isolated to
+	 * a single line, the cursor moved to the start of the change, and
+	 * then, subsequent 'u' commands would not move it again. (It has been
+	 * pointed out that users used multiple undo commands to get the cursor
+	 * to the start of the changed text.)  Nvi toggles between the cursor
+	 * position before and after the change was made.  One final issue is
+	 * that historic vi only did this if the user had not moved off of the
+	 * line before entering the undo command; otherwise, vi would move the
+	 * cursor to the most attractive position on the changed line.
+	 *
+	 * It would be difficult to match historic practice in this area. You
+	 * not only have to know that the changes were isolated to one line,
+	 * but whether it was the first or second undo command as well.  And,
+	 * to completely match historic practice, we'd have to track users line
+	 * changes, too.  This isn't worth the effort.
+	 */
+	ep = sp->ep;
+	if (!F_ISSET(ep, F_UNDO)) {
+		F_SET(ep, F_UNDO);
+		ep->lundo = BACKWARD;
+	} else if (!F_ISSET(vp, VC_ISDOT))
+		ep->lundo = ep->lundo == BACKWARD ? FORWARD : BACKWARD;
+
+	switch (ep->lundo) {
+	case BACKWARD:
+		return (log_backward(sp, &vp->m_final));
+	case FORWARD:
+		return (log_forward(sp, &vp->m_final));
+	default:
+		abort();
+	}
+	/* NOTREACHED */
+}