/*      $OpenBSD: vs_smap.c,v 1.9 2016/01/06 22:28:52 millert 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(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(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(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(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(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(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(SCR *sp, MARK *rp, recno_t count, scroll_t scmd, 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(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(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(SCR *sp, MARK *rp, recno_t count, scroll_t scmd, SMAP *smp)
{
        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(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(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(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(SCR *sp, SMAP *p, SMAP *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(SCR *sp, SMAP *p, SMAP *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(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(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, "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,
                            "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(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);
}