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[unix-history] / usr / src / usr.bin / more / position.c

/*
* Copyright (c) 1988 Mark Nudleman
* Copyright (c) 1988 Regents of the University of California.
* All rights reserved.
*
* %sccs.include.redist.c%
*/

#ifndef lint
static char sccsid[] = "@(#)position.c  5.7 (Berkeley) %G%";
#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);
}