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rcsid[] and sccsid[] and copyright[] are essentially unmaintained (and
unmaintainable).  these days, people use source.  these id's do not provide
any benefit, and do hurt the small install media
(the 33,000 line diff is essentially mechanical)
ok with the idea millert, ok dms

/*	$OpenBSD: vs_smap.c,v 1.7 2009/10/27 23:59:49 deraadt Exp $	*/

/*-
 * Copyright (c) 1993, 1994
 *	The Regents of the University of California.  All rights reserved.
 * Copyright (c) 1993, 1994, 1995, 1996
 *	Keith Bostic.  All rights reserved.
 *
 * See the LICENSE file for redistribution information.
 */

#include "config.h"

#include <sys/types.h>
#include <sys/queue.h>
#include <sys/time.h>

#include <bitstring.h>
#include <limits.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include "../common/common.h"
#include "vi.h"

static int	vs_deleteln(SCR *, int);
static int	vs_insertln(SCR *, int);
static int	vs_sm_delete(SCR *, recno_t);
static int	vs_sm_down(SCR *, MARK *, recno_t, scroll_t, SMAP *);
static int	vs_sm_erase(SCR *);
static int	vs_sm_insert(SCR *, recno_t);
static int	vs_sm_reset(SCR *, recno_t);
static int	vs_sm_up(SCR *, MARK *, recno_t, scroll_t, SMAP *);

/*
 * vs_change --
 *	Make a change to the screen.
 *
 * PUBLIC: int vs_change(SCR *, recno_t, lnop_t);
 */
int
vs_change(sp, lno, op)
	SCR *sp;
	recno_t lno;
	lnop_t op;
{
	VI_PRIVATE *vip;
	SMAP *p;
	size_t cnt, oldy, oldx;

	vip = VIP(sp);

	/*
	 * XXX
	 * Very nasty special case.  The historic vi code displays a single
	 * space (or a '$' if the list option is set) for the first line in
	 * an "empty" file.  If we "insert" a line, that line gets scrolled
	 * down, not repainted, so it's incorrect when we refresh the screen.
	 * The vi text input functions detect it explicitly and don't insert
	 * a new line.
	 *
	 * Check for line #2 before going to the end of the file.
	 */
	if (((op == LINE_APPEND && lno == 0) || (op == LINE_INSERT && lno == 1)) &&
	    !db_exist(sp, 2)) {
		lno = 1;
		op = LINE_RESET;
	}

	/* Appending is the same as inserting, if the line is incremented. */
	if (op == LINE_APPEND) {
		++lno;
		op = LINE_INSERT;
	}

	/* Ignore the change if the line is after the map. */
	if (lno > TMAP->lno)
		return (0);

	/*
	 * If the line is before the map, and it's a decrement, decrement
	 * the map.  If it's an increment, increment the map.  Otherwise,
	 * ignore it.
	 */
	if (lno < HMAP->lno) {
		switch (op) {
		case LINE_APPEND:
			abort();
			/* NOTREACHED */
		case LINE_DELETE:
			for (p = HMAP, cnt = sp->t_rows; cnt--; ++p)
				--p->lno;
			if (sp->lno >= lno)
				--sp->lno;
			F_SET(vip, VIP_N_RENUMBER);
			break;
		case LINE_INSERT:
			for (p = HMAP, cnt = sp->t_rows; cnt--; ++p)
				++p->lno;
			if (sp->lno >= lno)
				++sp->lno;
			F_SET(vip, VIP_N_RENUMBER);
			break;
		case LINE_RESET:
			break;
		}
		return (0);
	}

	F_SET(vip, VIP_N_REFRESH);

	/*
	 * Invalidate the line size cache, and invalidate the cursor if it's
	 * on this line,
	 */
	VI_SCR_CFLUSH(vip);
	if (sp->lno == lno)
		F_SET(vip, VIP_CUR_INVALID);

	/*
	 * If ex modifies the screen after ex output is already on the screen
	 * or if we've switched into ex canonical mode, don't touch it -- we'll
	 * get scrolling wrong, at best.
	 */
	if (!F_ISSET(sp, SC_TINPUT_INFO) &&
	    (F_ISSET(sp, SC_SCR_EXWROTE) || VIP(sp)->totalcount > 1)) {
		F_SET(vip, VIP_N_EX_REDRAW);
		return (0);
	}

	/* Save and restore the cursor for these routines. */
	(void)sp->gp->scr_cursor(sp, &oldy, &oldx);

	switch (op) {
	case LINE_DELETE:
		if (vs_sm_delete(sp, lno))
			return (1);
		F_SET(vip, VIP_N_RENUMBER);
		break;
	case LINE_INSERT:
		if (vs_sm_insert(sp, lno))
			return (1);
		F_SET(vip, VIP_N_RENUMBER);
		break;
	case LINE_RESET:
		if (vs_sm_reset(sp, lno))
			return (1);
		break;
	default:
		abort();
	}

	(void)sp->gp->scr_move(sp, oldy, oldx);
	return (0);
}

/*
 * vs_sm_fill --
 *	Fill in the screen map, placing the specified line at the
 *	right position.  There isn't any way to tell if an SMAP
 *	entry has been filled in, so this routine had better be
 *	called with P_FILL set before anything else is done.
 *
 * !!!
 * Unexported interface: if lno is OOBLNO, P_TOP means that the HMAP
 * slot is already filled in, P_BOTTOM means that the TMAP slot is
 * already filled in, and we just finish up the job.
 *
 * PUBLIC: int vs_sm_fill(SCR *, recno_t, pos_t);
 */
int
vs_sm_fill(sp, lno, pos)
	SCR *sp;
	recno_t lno;
	pos_t pos;
{
	SMAP *p, tmp;
	size_t cnt;

	/* Flush all cached information from the SMAP. */
	for (p = HMAP, cnt = sp->t_rows; cnt--; ++p)
		SMAP_FLUSH(p);

	/*
	 * If the map is filled, the screen must be redrawn.
	 *
	 * XXX
	 * This is a bug.  We should try and figure out if the desired line
	 * is already in the map or close by -- scrolling the screen would
	 * be a lot better than redrawing.
	 */
	F_SET(sp, SC_SCR_REDRAW);

	switch (pos) {
	case P_FILL:
		tmp.lno = 1;
		tmp.coff = 0;
		tmp.soff = 1;

		/* See if less than half a screen from the top. */
		if (vs_sm_nlines(sp,
		    &tmp, lno, HALFTEXT(sp)) <= HALFTEXT(sp)) {
			lno = 1;
			goto top;
		}

		/* See if less than half a screen from the bottom. */
		if (db_last(sp, &tmp.lno))
			return (1);
		tmp.coff = 0;
		tmp.soff = vs_screens(sp, tmp.lno, NULL);
		if (vs_sm_nlines(sp,
		    &tmp, lno, HALFTEXT(sp)) <= HALFTEXT(sp)) {
			TMAP->lno = tmp.lno;
			TMAP->coff = tmp.coff;
			TMAP->soff = tmp.soff;
			goto bottom;
		}
		goto middle;
	case P_TOP:
		if (lno != OOBLNO) {
top:			HMAP->lno = lno;
			HMAP->coff = 0;
			HMAP->soff = 1;
		}
		/* If we fail, just punt. */
		for (p = HMAP, cnt = sp->t_rows; --cnt; ++p)
			if (vs_sm_next(sp, p, p + 1))
				goto err;
		break;
	case P_MIDDLE:
		/* If we fail, guess that the file is too small. */
middle:		p = HMAP + sp->t_rows / 2;
		p->lno = lno;
		p->coff = 0;
		p->soff = 1;
		for (; p > HMAP; --p)
			if (vs_sm_prev(sp, p, p - 1)) {
				lno = 1;
				goto top;
			}

		/* If we fail, just punt. */
		p = HMAP + sp->t_rows / 2;
		for (; p < TMAP; ++p)
			if (vs_sm_next(sp, p, p + 1))
				goto err;
		break;
	case P_BOTTOM:
		if (lno != OOBLNO) {
			TMAP->lno = lno;
			TMAP->coff = 0;
			TMAP->soff = vs_screens(sp, lno, NULL);
		}
		/* If we fail, guess that the file is too small. */
bottom:		for (p = TMAP; p > HMAP; --p)
			if (vs_sm_prev(sp, p, p - 1)) {
				lno = 1;
				goto top;
			}
		break;
	default:
		abort();
	}
	return (0);

	/*
	 * Try and put *something* on the screen.  If this fails, we have a
	 * serious hard error.
	 */
err:	HMAP->lno = 1;
	HMAP->coff = 0;
	HMAP->soff = 1;
	for (p = HMAP; p < TMAP; ++p)
		if (vs_sm_next(sp, p, p + 1))
			return (1);
	return (0);
}

/*
 * For the routines vs_sm_reset, vs_sm_delete and vs_sm_insert: if the
 * screen contains only a single line (whether because the screen is small
 * or the line large), it gets fairly exciting.  Skip the fun, set a flag
 * so the screen map is refilled and the screen redrawn, and return.  This
 * is amazingly slow, but it's not clear that anyone will care.
 */
#define	HANDLE_WEIRDNESS(cnt) {						\
	if ((cnt) >= sp->t_rows) {					\
		F_SET(sp, SC_SCR_REFORMAT);				\
		return (0);						\
	}								\
}

/*
 * vs_sm_delete --
 *	Delete a line out of the SMAP.
 */
static int
vs_sm_delete(sp, lno)
	SCR *sp;
	recno_t lno;
{
	SMAP *p, *t;
	size_t cnt_orig;

	/*
	 * Find the line in the map, and count the number of screen lines
	 * which display any part of the deleted line.
	 */
	for (p = HMAP; p->lno != lno; ++p);
	if (O_ISSET(sp, O_LEFTRIGHT))
		cnt_orig = 1;
	else
		for (cnt_orig = 1, t = p + 1;
		    t <= TMAP && t->lno == lno; ++cnt_orig, ++t);

	HANDLE_WEIRDNESS(cnt_orig);

	/* Delete that many lines from the screen. */
	(void)sp->gp->scr_move(sp, p - HMAP, 0);
	if (vs_deleteln(sp, cnt_orig))
		return (1);

	/* Shift the screen map up. */
	memmove(p, p + cnt_orig, (((TMAP - p) - cnt_orig) + 1) * sizeof(SMAP));

	/* Decrement the line numbers for the rest of the map. */
	for (t = TMAP - cnt_orig; p <= t; ++p)
		--p->lno;

	/* Display the new lines. */
	for (p = TMAP - cnt_orig;;) {
		if (p < TMAP && vs_sm_next(sp, p, p + 1))
			return (1);
		/* vs_sm_next() flushed the cache. */
		if (vs_line(sp, ++p, NULL, NULL))
			return (1);
		if (p == TMAP)
			break;
	}
	return (0);
}

/*
 * vs_sm_insert --
 *	Insert a line into the SMAP.
 */
static int
vs_sm_insert(sp, lno)
	SCR *sp;
	recno_t lno;
{
	SMAP *p, *t;
	size_t cnt_orig, cnt, coff;

	/* Save the offset. */
	coff = HMAP->coff;

	/*
	 * Find the line in the map, find out how many screen lines
	 * needed to display the line.
	 */
	for (p = HMAP; p->lno != lno; ++p);

	cnt_orig = vs_screens(sp, lno, NULL);
	HANDLE_WEIRDNESS(cnt_orig);

	/*
	 * The lines left in the screen override the number of screen
	 * lines in the inserted line.
	 */
	cnt = (TMAP - p) + 1;
	if (cnt_orig > cnt)
		cnt_orig = cnt;

	/* Push down that many lines. */
	(void)sp->gp->scr_move(sp, p - HMAP, 0);
	if (vs_insertln(sp, cnt_orig))
		return (1);

	/* Shift the screen map down. */
	memmove(p + cnt_orig, p, (((TMAP - p) - cnt_orig) + 1) * sizeof(SMAP));

	/* Increment the line numbers for the rest of the map. */
	for (t = p + cnt_orig; t <= TMAP; ++t)
		++t->lno;

	/* Fill in the SMAP for the new lines, and display. */
	for (cnt = 1, t = p; cnt <= cnt_orig; ++t, ++cnt) {
		t->lno = lno;
		t->coff = coff;
		t->soff = cnt;
		SMAP_FLUSH(t);
		if (vs_line(sp, t, NULL, NULL))
			return (1);
	}
	return (0);
}

/*
 * vs_sm_reset --
 *	Reset a line in the SMAP.
 */
static int
vs_sm_reset(sp, lno)
	SCR *sp;
	recno_t lno;
{
	SMAP *p, *t;
	size_t cnt_orig, cnt_new, cnt, diff;

	/*
	 * See if the number of on-screen rows taken up by the old display
	 * for the line is the same as the number needed for the new one.
	 * If so, repaint, otherwise do it the hard way.
	 */
	for (p = HMAP; p->lno != lno; ++p);
	if (O_ISSET(sp, O_LEFTRIGHT)) {
		t = p;
		cnt_orig = cnt_new = 1;
	} else {
		for (cnt_orig = 0,
		    t = p; t <= TMAP && t->lno == lno; ++cnt_orig, ++t);
		cnt_new = vs_screens(sp, lno, NULL);
	}

	HANDLE_WEIRDNESS(cnt_orig);

	if (cnt_orig == cnt_new) {
		do {
			SMAP_FLUSH(p);
			if (vs_line(sp, p, NULL, NULL))
				return (1);
		} while (++p < t);
		return (0);
	}

	if (cnt_orig < cnt_new) {
		/* Get the difference. */
		diff = cnt_new - cnt_orig;

		/*
		 * The lines left in the screen override the number of screen
		 * lines in the inserted line.
		 */
		cnt = (TMAP - p) + 1;
		if (diff > cnt)
			diff = cnt;

		/* If there are any following lines, push them down. */
		if (cnt > 1) {
			(void)sp->gp->scr_move(sp, p - HMAP, 0);
			if (vs_insertln(sp, diff))
				return (1);

			/* Shift the screen map down. */
			memmove(p + diff, p,
			    (((TMAP - p) - diff) + 1) * sizeof(SMAP));
		}

		/* Fill in the SMAP for the replaced line, and display. */
		for (cnt = 1, t = p; cnt_new-- && t <= TMAP; ++t, ++cnt) {
			t->lno = lno;
			t->soff = cnt;
			SMAP_FLUSH(t);
			if (vs_line(sp, t, NULL, NULL))
				return (1);
		}
	} else {
		/* Get the difference. */
		diff = cnt_orig - cnt_new;

		/* Delete that many lines from the screen. */
		(void)sp->gp->scr_move(sp, p - HMAP, 0);
		if (vs_deleteln(sp, diff))
			return (1);

		/* Shift the screen map up. */
		memmove(p, p + diff, (((TMAP - p) - diff) + 1) * sizeof(SMAP));

		/* Fill in the SMAP for the replaced line, and display. */
		for (cnt = 1, t = p; cnt_new--; ++t, ++cnt) {
			t->lno = lno;
			t->soff = cnt;
			SMAP_FLUSH(t);
			if (vs_line(sp, t, NULL, NULL))
				return (1);
		}

		/* Display the new lines at the bottom of the screen. */
		for (t = TMAP - diff;;) {
			if (t < TMAP && vs_sm_next(sp, t, t + 1))
				return (1);
			/* vs_sm_next() flushed the cache. */
			if (vs_line(sp, ++t, NULL, NULL))
				return (1);
			if (t == TMAP)
				break;
		}
	}
	return (0);
}

/*
 * vs_sm_scroll
 *	Scroll the SMAP up/down count logical lines.  Different
 *	semantics based on the vi command, *sigh*.
 *
 * PUBLIC: int vs_sm_scroll(SCR *, MARK *, recno_t, scroll_t);
 */
int
vs_sm_scroll(sp, rp, count, scmd)
	SCR *sp;
	MARK *rp;
	recno_t count;
	scroll_t scmd;
{
	SMAP *smp;

	/*
	 * Invalidate the cursor.  The line is probably going to change,
	 * (although for ^E and ^Y it may not).  In any case, the scroll
	 * routines move the cursor to draw things.
	 */
	F_SET(VIP(sp), VIP_CUR_INVALID);

	/* Find the cursor in the screen. */
	if (vs_sm_cursor(sp, &smp))
		return (1);

	switch (scmd) {
	case CNTRL_B:
	case CNTRL_U:
	case CNTRL_Y:
	case Z_CARAT:
		if (vs_sm_down(sp, rp, count, scmd, smp))
			return (1);
		break;
	case CNTRL_D:
	case CNTRL_E:
	case CNTRL_F:
	case Z_PLUS:
		if (vs_sm_up(sp, rp, count, scmd, smp))
			return (1);
		break;
	default:
		abort();
	}

	/*
	 * !!!
	 * If we're at the start of a line, go for the first non-blank.
	 * This makes it look like the old vi, even though we're moving
	 * around by logical lines, not physical ones.
	 *
	 * XXX
	 * In the presence of a long line, which has more than a screen
	 * width of leading spaces, this code can cause a cursor warp.
	 * Live with it.
	 */
	if (scmd != CNTRL_E && scmd != CNTRL_Y &&
	    rp->cno == 0 && nonblank(sp, rp->lno, &rp->cno))
		return (1);

	return (0);
}

/*
 * vs_sm_up --
 *	Scroll the SMAP up count logical lines.
 */
static int
vs_sm_up(sp, rp, count, scmd, smp)
	SCR *sp;
	MARK *rp;
	scroll_t scmd;
	recno_t count;
	SMAP *smp;
{
	int cursor_set, echanged, zset;
	SMAP *ssmp, s1, s2;

	/*
	 * Check to see if movement is possible.
	 *
	 * Get the line after the map.  If that line is a new one (and if
	 * O_LEFTRIGHT option is set, this has to be true), and the next
	 * line doesn't exist, and the cursor doesn't move, or the cursor
	 * isn't even on the screen, or the cursor is already at the last
	 * line in the map, it's an error.  If that test succeeded because
	 * the cursor wasn't at the end of the map, test to see if the map
	 * is mostly empty.
	 */
	if (vs_sm_next(sp, TMAP, &s1))
		return (1);
	if (s1.lno > TMAP->lno && !db_exist(sp, s1.lno)) {
		if (scmd == CNTRL_E || scmd == Z_PLUS || smp == TMAP) {
			v_eof(sp, NULL);
			return (1);
		}
		if (vs_sm_next(sp, smp, &s1))
			return (1);
		if (s1.lno > smp->lno && !db_exist(sp, s1.lno)) {
			v_eof(sp, NULL);
			return (1);
		}
	}

	/*
	 * Small screens: see vs_refresh.c section 6a.
	 *
	 * If it's a small screen, and the movement isn't larger than a
	 * screen, i.e some context will remain, open up the screen and
	 * display by scrolling.  In this case, the cursor moves down one
	 * line for each line displayed.  Otherwise, erase/compress and
	 * repaint, and move the cursor to the first line in the screen.
	 * Note, the ^F command is always in the latter case, for historical
	 * reasons.
	 */
	cursor_set = 0;
	if (IS_SMALL(sp)) {
		if (count >= sp->t_maxrows || scmd == CNTRL_F) {
			s1 = TMAP[0];
			if (vs_sm_erase(sp))
				return (1);
			for (; count--; s1 = s2) {
				if (vs_sm_next(sp, &s1, &s2))
					return (1);
				if (s2.lno != s1.lno && !db_exist(sp, s2.lno))
					break;
			}
			TMAP[0] = s2;
			if (vs_sm_fill(sp, OOBLNO, P_BOTTOM))
				return (1);
			return (vs_sm_position(sp, rp, 0, P_TOP));
		}
		cursor_set = scmd == CNTRL_E || vs_sm_cursor(sp, &ssmp);
		for (; count &&
		    sp->t_rows != sp->t_maxrows; --count, ++sp->t_rows) {
			if (vs_sm_next(sp, TMAP, &s1))
				return (1);
			if (TMAP->lno != s1.lno && !db_exist(sp, s1.lno))
				break;
			*++TMAP = s1;
			/* vs_sm_next() flushed the cache. */
			if (vs_line(sp, TMAP, NULL, NULL))
				return (1);

			if (!cursor_set)
				++ssmp;
		}
		if (!cursor_set) {
			rp->lno = ssmp->lno;
			rp->cno = ssmp->c_sboff;
		}
		if (count == 0)
			return (0);
	}

	for (echanged = zset = 0; count; --count) {
		/* Decide what would show up on the screen. */
		if (vs_sm_next(sp, TMAP, &s1))
			return (1);

		/* If the line doesn't exist, we're done. */
		if (TMAP->lno != s1.lno && !db_exist(sp, s1.lno))
			break;

		/* Scroll the screen cursor up one logical line. */
		if (vs_sm_1up(sp))
			return (1);
		switch (scmd) {
		case CNTRL_E:
			if (smp > HMAP)
				--smp;
			else
				echanged = 1;
			break;
		case Z_PLUS:
			if (zset) {
				if (smp > HMAP)
					--smp;
			} else {
				smp = TMAP;
				zset = 1;
			}
			/* FALLTHROUGH */
		default:
			break;
		}
	}

	if (cursor_set)
		return(0);

	switch (scmd) {
	case CNTRL_E:
		/*
		 * On a ^E that was forced to change lines, try and keep the
		 * cursor as close as possible to the last position, but also
		 * set it up so that the next "real" movement will return the
		 * cursor to the closest position to the last real movement.
		 */
		if (echanged) {
			rp->lno = smp->lno;
			rp->cno = vs_colpos(sp, smp->lno,
			    (O_ISSET(sp, O_LEFTRIGHT) ? 
			    smp->coff : (smp->soff - 1) * sp->cols) +
			    sp->rcm % sp->cols);
		}
		return (0);
	case CNTRL_F:
		/*
		 * If there are more lines, the ^F command is positioned at
		 * the first line of the screen.
		 */
		if (!count) {
			smp = HMAP;
			break;
		}
		/* FALLTHROUGH */
	case CNTRL_D:
		/*
		 * The ^D and ^F commands move the cursor towards EOF
		 * if there are more lines to move.  Check to be sure
		 * the lines actually exist.  (They may not if the
		 * file is smaller than the screen.)
		 */
		for (; count; --count, ++smp)
			if (smp == TMAP || !db_exist(sp, smp[1].lno))
				break;
		break;
	case Z_PLUS:
		 /* The z+ command moves the cursor to the first new line. */
		break;
	default:
		abort();
	}

	if (!SMAP_CACHE(smp) && vs_line(sp, smp, NULL, NULL))
		return (1);
	rp->lno = smp->lno;
	rp->cno = smp->c_sboff;
	return (0);
}

/*
 * vs_sm_1up --
 *	Scroll the SMAP up one.
 *
 * PUBLIC: int vs_sm_1up(SCR *);
 */
int
vs_sm_1up(sp)
	SCR *sp;
{
	/*
	 * Delete the top line of the screen.  Shift the screen map
	 * up and display a new line at the bottom of the screen.
	 */
	(void)sp->gp->scr_move(sp, 0, 0);
	if (vs_deleteln(sp, 1))
		return (1);

	/* One-line screens can fail. */
	if (IS_ONELINE(sp)) {
		if (vs_sm_next(sp, TMAP, TMAP))
			return (1);
	} else {
		memmove(HMAP, HMAP + 1, (sp->rows - 1) * sizeof(SMAP));
		if (vs_sm_next(sp, TMAP - 1, TMAP))
			return (1);
	}
	/* vs_sm_next() flushed the cache. */
	return (vs_line(sp, TMAP, NULL, NULL));
}

/*
 * vs_deleteln --
 *	Delete a line a la curses, make sure to put the information
 *	line and other screens back.
 */
static int
vs_deleteln(sp, cnt)
	SCR *sp;
	int cnt;
{
	GS *gp;
	size_t oldy, oldx;

	gp = sp->gp;
	if (IS_ONELINE(sp))
		(void)gp->scr_clrtoeol(sp);
	else {
		(void)gp->scr_cursor(sp, &oldy, &oldx);
		while (cnt--) {
			(void)gp->scr_deleteln(sp);
			(void)gp->scr_move(sp, LASTLINE(sp), 0);
			(void)gp->scr_insertln(sp);
			(void)gp->scr_move(sp, oldy, oldx);
		}
	}
	return (0);
}

/*
 * vs_sm_down --
 *	Scroll the SMAP down count logical lines.
 */
static int
vs_sm_down(sp, rp, count, scmd, smp)
	SCR *sp;
	MARK *rp;
	recno_t count;
	SMAP *smp;
	scroll_t scmd;
{
	SMAP *ssmp, s1, s2;
	int cursor_set, ychanged, zset;

	/* Check to see if movement is possible. */
	if (HMAP->lno == 1 &&
	    (O_ISSET(sp, O_LEFTRIGHT) || HMAP->soff == 1) &&
	    (scmd == CNTRL_Y || scmd == Z_CARAT || smp == HMAP)) {
		v_sof(sp, NULL);
		return (1);
	}

	/*
	 * Small screens: see vs_refresh.c section 6a.
	 *
	 * If it's a small screen, and the movement isn't larger than a
	 * screen, i.e some context will remain, open up the screen and
	 * display by scrolling.  In this case, the cursor moves up one
	 * line for each line displayed.  Otherwise, erase/compress and
	 * repaint, and move the cursor to the first line in the screen.
	 * Note, the ^B command is always in the latter case, for historical
	 * reasons.
	 */
	cursor_set = scmd == CNTRL_Y;
	if (IS_SMALL(sp)) {
		if (count >= sp->t_maxrows || scmd == CNTRL_B) {
			s1 = HMAP[0];
			if (vs_sm_erase(sp))
				return (1);
			for (; count--; s1 = s2) {
				if (vs_sm_prev(sp, &s1, &s2))
					return (1);
				if (s2.lno == 1 &&
				    (O_ISSET(sp, O_LEFTRIGHT) || s2.soff == 1))
					break;
			}
			HMAP[0] = s2;
			if (vs_sm_fill(sp, OOBLNO, P_TOP))
				return (1);
			return (vs_sm_position(sp, rp, 0, P_BOTTOM));
		}
		cursor_set = scmd == CNTRL_Y || vs_sm_cursor(sp, &ssmp);
		for (; count &&
		    sp->t_rows != sp->t_maxrows; --count, ++sp->t_rows) {
			if (HMAP->lno == 1 &&
			    (O_ISSET(sp, O_LEFTRIGHT) || HMAP->soff == 1))
				break;
			++TMAP;
			if (vs_sm_1down(sp))
				return (1);
		}
		if (!cursor_set) {
			rp->lno = ssmp->lno;
			rp->cno = ssmp->c_sboff;
		}
		if (count == 0)
			return (0);
	}

	for (ychanged = zset = 0; count; --count) {
		/* If the line doesn't exist, we're done. */
		if (HMAP->lno == 1 &&
		    (O_ISSET(sp, O_LEFTRIGHT) || HMAP->soff == 1))
			break;

		/* Scroll the screen and cursor down one logical line. */
		if (vs_sm_1down(sp))
			return (1);
		switch (scmd) {
		case CNTRL_Y:
			if (smp < TMAP)
				++smp;
			else
				ychanged = 1;
			break;
		case Z_CARAT:
			if (zset) {
				if (smp < TMAP)
					++smp;
			} else {
				smp = HMAP;
				zset = 1;
			}
			/* FALLTHROUGH */
		default:
			break;
		}
	}

	if (scmd != CNTRL_Y && cursor_set)
		return(0);

	switch (scmd) {
	case CNTRL_B:
		/*
		 * If there are more lines, the ^B command is positioned at
		 * the last line of the screen.  However, the line may not
		 * exist.
		 */
		if (!count) {
			for (smp = TMAP; smp > HMAP; --smp)
				if (db_exist(sp, smp->lno))
					break;
			break;
		}
		/* FALLTHROUGH */
	case CNTRL_U:
		/*
		 * The ^B and ^U commands move the cursor towards SOF
		 * if there are more lines to move.
		 */
		if (count < smp - HMAP)
			smp -= count;
		else
			smp = HMAP;
		break;
	case CNTRL_Y:
		/*
		 * On a ^Y that was forced to change lines, try and keep the
		 * cursor as close as possible to the last position, but also
		 * set it up so that the next "real" movement will return the
		 * cursor to the closest position to the last real movement.
		 */
		if (ychanged) {
			rp->lno = smp->lno;
			rp->cno = vs_colpos(sp, smp->lno,
			    (O_ISSET(sp, O_LEFTRIGHT) ? 
			    smp->coff : (smp->soff - 1) * sp->cols) +
			    sp->rcm % sp->cols);
		}
		return (0);
	case Z_CARAT:
		 /* The z^ command moves the cursor to the first new line. */
		break;
	default:
		abort();
	}

	if (!SMAP_CACHE(smp) && vs_line(sp, smp, NULL, NULL))
		return (1);
	rp->lno = smp->lno;
	rp->cno = smp->c_sboff;
	return (0);
}

/*
 * vs_sm_erase --
 *	Erase the small screen area for the scrolling functions.
 */
static int
vs_sm_erase(sp)
	SCR *sp;
{
	GS *gp;

	gp = sp->gp;
	(void)gp->scr_move(sp, LASTLINE(sp), 0);
	(void)gp->scr_clrtoeol(sp);
	for (; sp->t_rows > sp->t_minrows; --sp->t_rows, --TMAP) {
		(void)gp->scr_move(sp, TMAP - HMAP, 0);
		(void)gp->scr_clrtoeol(sp);
	}
	return (0);
}

/*
 * vs_sm_1down --
 *	Scroll the SMAP down one.
 *
 * PUBLIC: int vs_sm_1down(SCR *);
 */
int
vs_sm_1down(sp)
	SCR *sp;
{
	/*
	 * Insert a line at the top of the screen.  Shift the screen map
	 * down and display a new line at the top of the screen.
	 */
	(void)sp->gp->scr_move(sp, 0, 0);
	if (vs_insertln(sp, 1))
		return (1);

	/* One-line screens can fail. */
	if (IS_ONELINE(sp)) {
		if (vs_sm_prev(sp, HMAP, HMAP))
			return (1);
	} else {
		memmove(HMAP + 1, HMAP, (sp->rows - 1) * sizeof(SMAP));
		if (vs_sm_prev(sp, HMAP + 1, HMAP))
			return (1);
	}
	/* vs_sm_prev() flushed the cache. */
	return (vs_line(sp, HMAP, NULL, NULL));
}

/*
 * vs_insertln --
 *	Insert a line a la curses, make sure to put the information
 *	line and other screens back.
 */
static int
vs_insertln(sp, cnt)
	SCR *sp;
	int cnt;
{
	GS *gp;
	size_t oldy, oldx;

	gp = sp->gp;
	if (IS_ONELINE(sp)) {
		(void)gp->scr_move(sp, LASTLINE(sp), 0);
		(void)gp->scr_clrtoeol(sp);
	} else {
		(void)gp->scr_cursor(sp, &oldy, &oldx);
		while (cnt--) {
			(void)gp->scr_move(sp, LASTLINE(sp) - 1, 0);
			(void)gp->scr_deleteln(sp);
			(void)gp->scr_move(sp, oldy, oldx);
			(void)gp->scr_insertln(sp);
		}
	}
	return (0);
}

/*
 * vs_sm_next --
 *	Fill in the next entry in the SMAP.
 *
 * PUBLIC: int vs_sm_next(SCR *, SMAP *, SMAP *);
 */
int
vs_sm_next(sp, p, t)
	SCR *sp;
	SMAP *p, *t;
{
	size_t lcnt;

	SMAP_FLUSH(t);
	if (O_ISSET(sp, O_LEFTRIGHT)) {
		t->lno = p->lno + 1;
		t->coff = p->coff;
	} else {
		lcnt = vs_screens(sp, p->lno, NULL);
		if (lcnt == p->soff) {
			t->lno = p->lno + 1;
			t->soff = 1;
		} else {
			t->lno = p->lno;
			t->soff = p->soff + 1;
		}
	}
	return (0);
}

/*
 * vs_sm_prev --
 *	Fill in the previous entry in the SMAP.
 *
 * PUBLIC: int vs_sm_prev(SCR *, SMAP *, SMAP *);
 */
int
vs_sm_prev(sp, p, t)
	SCR *sp;
	SMAP *p, *t;
{
	SMAP_FLUSH(t);
	if (O_ISSET(sp, O_LEFTRIGHT)) {
		t->lno = p->lno - 1;
		t->coff = p->coff;
	} else {
		if (p->soff != 1) {
			t->lno = p->lno;
			t->soff = p->soff - 1;
		} else {
			t->lno = p->lno - 1;
			t->soff = vs_screens(sp, t->lno, NULL);
		}
	}
	return (t->lno == 0);
}

/*
 * vs_sm_cursor --
 *	Return the SMAP entry referenced by the cursor.
 *
 * PUBLIC: int vs_sm_cursor(SCR *, SMAP **);
 */
int
vs_sm_cursor(sp, smpp)
	SCR *sp;
	SMAP **smpp;
{
	SMAP *p;

	/* See if the cursor is not in the map. */
	if (sp->lno < HMAP->lno || sp->lno > TMAP->lno)
		return (1);

	/* Find the first occurrence of the line. */
	for (p = HMAP; p->lno != sp->lno; ++p);

	/* Fill in the map information until we find the right line. */
	for (; p <= TMAP; ++p) {
		/* Short lines are common and easy to detect. */
		if (p != TMAP && (p + 1)->lno != p->lno) {
			*smpp = p;
			return (0);
		}
		if (!SMAP_CACHE(p) && vs_line(sp, p, NULL, NULL))
			return (1);
		if (p->c_eboff >= sp->cno) {
			*smpp = p;
			return (0);
		}
	}

	/* It was past the end of the map after all. */
	return (1);
}

/*
 * vs_sm_position --
 *	Return the line/column of the top, middle or last line on the screen.
 *	(The vi H, M and L commands.)  Here because only the screen routines
 *	know what's really out there.
 *
 * PUBLIC: int vs_sm_position(SCR *, MARK *, u_long, pos_t);
 */
int
vs_sm_position(sp, rp, cnt, pos)
	SCR *sp;
	MARK *rp;
	u_long cnt;
	pos_t pos;
{
	SMAP *smp;
	recno_t last;

	switch (pos) {
	case P_TOP:
		/*
		 * !!!
		 * Historically, an invalid count to the H command failed.
		 * We do nothing special here, just making sure that H in
		 * an empty screen works.
		 */
		if (cnt > TMAP - HMAP)
			goto sof;
		smp = HMAP + cnt;
		if (cnt && !db_exist(sp, smp->lno)) {
sof:			msgq(sp, M_BERR, "220|Movement past the end-of-screen");
			return (1);
		}
		break;
	case P_MIDDLE:
		/*
		 * !!!
		 * Historically, a count to the M command was ignored.
		 * If the screen isn't filled, find the middle of what's
		 * real and move there.
		 */
		if (!db_exist(sp, TMAP->lno)) {
			if (db_last(sp, &last))
				return (1);
			for (smp = TMAP; smp->lno > last && smp > HMAP; --smp);
			if (smp > HMAP)
				smp -= (smp - HMAP) / 2;
		} else
			smp = (HMAP + (TMAP - HMAP) / 2) + cnt;
		break;
	case P_BOTTOM:
		/*
		 * !!!
		 * Historically, an invalid count to the L command failed.
		 * If the screen isn't filled, find the bottom of what's
		 * real and try to offset from there.
		 */
		if (cnt > TMAP - HMAP)
			goto eof;
		smp = TMAP - cnt;
		if (!db_exist(sp, smp->lno)) {
			if (db_last(sp, &last))
				return (1);
			for (; smp->lno > last && smp > HMAP; --smp);
			if (cnt > smp - HMAP) {
eof:				msgq(sp, M_BERR,
			    "221|Movement past the beginning-of-screen");
				return (1);
			}
			smp -= cnt;
		}
		break;
	default:
		abort();
	}

	/* Make sure that the cached information is valid. */
	if (!SMAP_CACHE(smp) && vs_line(sp, smp, NULL, NULL))
		return (1);
	rp->lno = smp->lno;
	rp->cno = smp->c_sboff;

	return (0);
}

/*
 * vs_sm_nlines --
 *	Return the number of screen lines from an SMAP entry to the
 *	start of some file line, less than a maximum value.
 *
 * PUBLIC: recno_t vs_sm_nlines(SCR *, SMAP *, recno_t, size_t);
 */
recno_t
vs_sm_nlines(sp, from_sp, to_lno, max)
	SCR *sp;
	SMAP *from_sp;
	recno_t to_lno;
	size_t max;
{
	recno_t lno, lcnt;

	if (O_ISSET(sp, O_LEFTRIGHT))
		return (from_sp->lno > to_lno ?
		    from_sp->lno - to_lno : to_lno - from_sp->lno);

	if (from_sp->lno == to_lno)
		return (from_sp->soff - 1);

	if (from_sp->lno > to_lno) {
		lcnt = from_sp->soff - 1;	/* Correct for off-by-one. */
		for (lno = from_sp->lno; --lno >= to_lno && lcnt <= max;)
			lcnt += vs_screens(sp, lno, NULL);
	} else {
		lno = from_sp->lno;
		lcnt = (vs_screens(sp, lno, NULL) - from_sp->soff) + 1;
		for (; ++lno < to_lno && lcnt <= max;)
			lcnt += vs_screens(sp, lno, NULL);
	}
	return (lcnt);
}