Category : Files from Magazines
Archive   : TREE_DDJ.ZIP
Filename : BITMAP.C

C Chest Listings (JULY '86)

.MDNM/ Listing 2 -- bitmap.c
------------------------------------------------------------------------------
1 /* BITMAP.C makebitmap, setbit, testbit: bit map manipulation
2 * routines.
3 *
4 * Copyright (c) 1985,1986 Allen I. Holub, all rights reserved.
5 *
6 * These routines originally appeared in the June, 1985, C Chest (DDJ
7 * #104). They are reproduced here in a stripped-down version.
8 * Please see that column for more information about how they work.
9 */
10
11 extern char *calloc ( unsigned, unsigned );
12
13 typedef char BITMAP;
14
15 /*----------------------------------------------------------------------*/
16
17 BITMAP *makebitmap( size )
18 unsigned size;
19 {
20 /* Make a bit map for "size" bits. */
21 /* Return a pointer to the map or NULL if we couldn't make it. */
22
23 unsigned *map, numbytes;
24
25 numbytes = (size >> 3) + ((size & 0x07) ? 1 : 0 ) ;
26
27 if( map = (unsigned *) calloc( numbytes + sizeof(unsigned) ,1 ) )
28 *map = size;
29
30 return (BITMAP *) map;
31 }
32
33 /* ------------------------------------------------------------------- */
34
35 setbit( c, map, val )
36 unsigned c, val;
37 char *map;
38 {
39 /* Set bit c in the map to val. */
40 /* If c > map size, 0 is returned, else 1 is returned. */
41
42 if( c >= *(unsigned *)map ) /* if c >= map size */
43 return 0;
44
45 map += sizeof(unsigned); /* Skip past size */
46
47 if( val ) map[c >> 3] |= 1 << (c & 0x07) ;
48 else map[c >> 3] &= ~(1 << (c & 0x07)) ;
49
50 return( 1 );
51 }
52
53 /* ------------------------------------------------------------------- */
54
55 testbit( c, map )
56 unsigned c;
57 char *map;
58 {
59 /* Return 1 if the bit corresponding to c in map is set. */
60 /* 0 if it is not. */
61
62 if( c >= *(unsigned *)map )
63 return 0;
64
65 map += sizeof(unsigned);
66
67 return( map[ c >> 3 ] & (1 << (c & 0x07)) );
68 }