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position.c revision 1.1 
      1 /*
      2  * Copyright (c) 1988 Mark Nudleman
      3  * Copyright (c) 1988, 1993
      4  *	The Regents of the University of California.  All rights reserved.
      5  *
      6  * Redistribution and use in source and binary forms, with or without
      7  * modification, are permitted provided that the following conditions
      8  * are met:
      9  * 1. Redistributions of source code must retain the above copyright
     10  *    notice, this list of conditions and the following disclaimer.
     11  * 2. Redistributions in binary form must reproduce the above copyright
     12  *    notice, this list of conditions and the following disclaimer in the
     13  *    documentation and/or other materials provided with the distribution.
     14  * 3. All advertising materials mentioning features or use of this software
     15  *    must display the following acknowledgement:
     16  *	This product includes software developed by the University of
     17  *	California, Berkeley and its contributors.
     18  * 4. Neither the name of the University nor the names of its contributors
     19  *    may be used to endorse or promote products derived from this software
     20  *    without specific prior written permission.
     21  *
     22  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
     23  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     24  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     25  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
     26  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     27  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     28  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     29  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     30  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     31  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     32  * SUCH DAMAGE.
     33  */
     34 
     35 #ifndef lint
     36 static char sccsid[] = "@(#)position.c	8.1 (Berkeley) 6/6/93";
     37 #endif /* not lint */
     38 
     39 /*
     40  * Routines dealing with the "position" table.
     41  * This is a table which tells the position (in the input file) of the
     42  * first char on each currently displayed line.
     43  *
     44  * {{ The position table is scrolled by moving all the entries.
     45  *    Would be better to have a circular table
     46  *    and just change a couple of pointers. }}
     47  */
     48 
     49 #include <sys/types.h>
     50 #include <less.h>
     51 
     52 static off_t *table;		/* The position table */
     53 static int tablesize;
     54 
     55 extern int sc_height;
     56 
     57 /*
     58  * Return the starting file position of a line displayed on the screen.
     59  * The line may be specified as a line number relative to the top
     60  * of the screen, but is usually one of these special cases:
     61  *	the top (first) line on the screen
     62  *	the second line on the screen
     63  *	the bottom line on the screen
     64  *	the line after the bottom line on the screen
     65  */
     66 off_t
     67 position(where)
     68 	int where;
     69 {
     70 	switch (where)
     71 	{
     72 	case BOTTOM:
     73 		where = sc_height - 2;
     74 		break;
     75 	case BOTTOM_PLUS_ONE:
     76 		where = sc_height - 1;
     77 		break;
     78 	case MIDDLE:
     79 		where = sc_height / 2;
     80 	}
     81 	return (table[where]);
     82 }
     83 
     84 /*
     85  * Add a new file position to the bottom of the position table.
     86  */
     87 add_forw_pos(pos)
     88 	off_t pos;
     89 {
     90 	register int i;
     91 
     92 	/*
     93 	 * Scroll the position table up.
     94 	 */
     95 	for (i = 1;  i < sc_height;  i++)
     96 		table[i-1] = table[i];
     97 	table[sc_height - 1] = pos;
     98 }
     99 
    100 /*
    101  * Add a new file position to the top of the position table.
    102  */
    103 add_back_pos(pos)
    104 	off_t pos;
    105 {
    106 	register int i;
    107 
    108 	/*
    109 	 * Scroll the position table down.
    110 	 */
    111 	for (i = sc_height - 1;  i > 0;  i--)
    112 		table[i] = table[i-1];
    113 	table[0] = pos;
    114 }
    115 
    116 copytable()
    117 {
    118 	register int a, b;
    119 
    120 	for (a = 0; a < sc_height && table[a] == NULL_POSITION; a++);
    121 	for (b = 0; a < sc_height; a++, b++) {
    122 		table[b] = table[a];
    123 		table[a] = NULL_POSITION;
    124 	}
    125 }
    126 
    127 /*
    128  * Initialize the position table, done whenever we clear the screen.
    129  */
    130 pos_clear()
    131 {
    132 	register int i;
    133 	extern char *malloc(), *realloc();
    134 
    135 	if (table == 0) {
    136 		tablesize = sc_height > 25 ? sc_height : 25;
    137 		table = (off_t *)malloc(tablesize * sizeof *table);
    138 	} else if (sc_height >= tablesize) {
    139 		tablesize = sc_height;
    140 		table = (off_t *)realloc(table, tablesize * sizeof *table);
    141 	}
    142 
    143 	for (i = 0;  i < sc_height;  i++)
    144 		table[i] = NULL_POSITION;
    145 }
    146 
    147 /*
    148  * See if the byte at a specified position is currently on the screen.
    149  * Check the position table to see if the position falls within its range.
    150  * Return the position table entry if found, -1 if not.
    151  */
    152 onscreen(pos)
    153 	off_t pos;
    154 {
    155 	register int i;
    156 
    157 	if (pos < table[0])
    158 		return (-1);
    159 	for (i = 1;  i < sc_height;  i++)
    160 		if (pos < table[i])
    161 			return (i-1);
    162 	return (-1);
    163 }
    164