homework/bitmap.c

   1 /*
   2  * Compile with:
   3  * gcc bitmap.c -o bitmap -Wall -W -Wextra -ansi -pedantic
   4  */
   5
   6 #include <limits.h>    /* for CHAR_BIT */
   7 #include <stdio.h>
   8 #include <stdlib.h>
   9 #include <string.h>    /* for memset() */
  10
  11 /* #define DEBUG */
  12 #ifdef DEBUG
  13 #define DPRINTF(x) printf x
  14 #else
  15 #define DPRINTF(x)
  16 #endif
  17
  18 /* Function prototypes */
  19 int is_blk_free(const unsigned char *array, unsigned int nblk);
  20 void print_blks(const unsigned char *array, unsigned int nblks);
  21 void diep(const char *s);
  22
  23 int main(int argc, char *argv[])
  24 {
  25     unsigned char *array;
  26     unsigned int i, narr, nblks, u;
  27
  28     /* Check argument count */
  29     if (argc != 2) {
  30         fprintf(stderr, "Usage: %s nblocks\n", argv[0]);
  31         exit(EXIT_FAILURE);
  32     }
  33
  34     /* Get number of blocks */
  35     nblks = (unsigned int) strtoul(argv[1], NULL, 10);
  36     u = nblks - CHAR_BIT * (nblks / CHAR_BIT);
  37     if (u == 0)
  38         narr = nblks / CHAR_BIT;
  39     else
  40         narr = nblks / CHAR_BIT + 1;
  41     printf("Requested nblks = %u\tAllocating narr = %u chars\n", nblks, narr);
  42
  43     /* Allocate memory for char bitmap */
  44     array = malloc(narr);
  45     if (array == NULL)
  46         diep("malloc");
  47
  48     /* Initialize all bits to 0 representing free blocks */
  49     memset(array, 0, narr);
  50
  51     /* Print blocks' status */
  52     print_blks(array, nblks);
  53
  54     /* Flag all blocks as used */
  55     for (i = 0; i < narr; i++)
  56         array[i] = 0xFF;
  57     print_blks(array, nblks);
  58
  59     /* Free bitmap */
  60     free(array);
  61
  62     return EXIT_SUCCESS;
  63 }
  64
  65 int is_blk_free(const unsigned char *array, unsigned int nblk)
  66 {
  67     unsigned int idx, u;
  68
  69     idx = nblk / CHAR_BIT;
  70     u = nblk - CHAR_BIT * idx;
  71     DPRINTF(("blk %u is in array %u and bitpos %u\n",
  72              nblk, idx, u));
  73
  74     return ((array[idx] & (1 << u)) == 0);
  75 }
  76
  77 void print_blks(const unsigned char *array, unsigned int nblks)
  78 {
  79     unsigned int i;
  80
  81     for (i = 0; i < nblks; i++)
  82         printf("blk[%04u] = %s\n",
  83                i, is_blk_free(array, i) ? "FREE" : "USED");
  84 }
  85
  86 void diep(const char *s)
  87 {
  88     perror(s);
  89     exit(EXIT_FAILURE);
  90 }