usr.bin/more/position.c

/*
 * Copyright (c) 1988 Mark Nudleman
 * Copyright (c) 1988 Regents of the University of California.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *      This product includes software developed by the University of
 *      California, Berkeley and its contributors.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#ifndef lint
static char sccsid[] = "@(#)position.c  5.7 (Berkeley) 6/1/90";
#endif /* not lint */

/*
 * Routines dealing with the "position" table.
 * This is a table which tells the position (in the input file) of the
 * first char on each currently displayed line.
 *
 * {{ The position table is scrolled by moving all the entries.
 *    Would be better to have a circular table
 *    and just change a couple of pointers. }}
 */

#include <sys/types.h>
#include <less.h>

static off_t *table;            /* The position table */
static int tablesize;

extern int sc_height;

/*
 * Return the starting file position of a line displayed on the screen.
 * The line may be specified as a line number relative to the top
 * of the screen, but is usually one of these special cases:
 *      the top (first) line on the screen
 *      the second line on the screen
 *      the bottom line on the screen
 *      the line after the bottom line on the screen
 */
off_t
position(where)
        int where;
{
        switch (where)
        {
        case BOTTOM:
                where = sc_height - 2;
                break;
        case BOTTOM_PLUS_ONE:
                where = sc_height - 1;
                break;
        case MIDDLE:
                where = sc_height / 2;
        }
        return (table[where]);
}

/*
 * Add a new file position to the bottom of the position table.
 */
add_forw_pos(pos)
        off_t pos;
{
        register int i;

        /*
         * Scroll the position table up.
         */
        for (i = 1;  i < sc_height;  i++)
                table[i-1] = table[i];
        table[sc_height - 1] = pos;
}

/*
 * Add a new file position to the top of the position table.
 */
add_back_pos(pos)
        off_t pos;
{
        register int i;

        /*
         * Scroll the position table down.
         */
        for (i = sc_height - 1;  i > 0;  i--)
                table[i] = table[i-1];
        table[0] = pos;
}

copytable()
{
        register int a, b;

        for (a = 0; a < sc_height && table[a] == NULL_POSITION; a++);
        for (b = 0; a < sc_height; a++, b++) {
                table[b] = table[a];
                table[a] = NULL_POSITION;
        }
}

/*
 * Initialize the position table, done whenever we clear the screen.
 */
pos_clear()
{
        register int i;
        extern char *malloc(), *realloc();

        if (table == 0) {
                tablesize = sc_height > 25 ? sc_height : 25;
                table = (off_t *)malloc(tablesize * sizeof *table);
        } else if (sc_height >= tablesize) {
                tablesize = sc_height;
                table = (off_t *)realloc(table, tablesize * sizeof *table);
        }

        for (i = 0;  i < sc_height;  i++)
                table[i] = NULL_POSITION;
}

/*
 * See if the byte at a specified position is currently on the screen.
 * Check the position table to see if the position falls within its range.
 * Return the position table entry if found, -1 if not.
 */
onscreen(pos)
        off_t pos;
{
        register int i;

        if (pos < table[0])
                return (-1);
        for (i = 1;  i < sc_height;  i++)
                if (pos < table[i])
                        return (i-1);
        return (-1);
}