bitmap

bitmap.c

#include <stdlib.h>
#include <stdio.h>

#define BITS_PER_LONG (sizeof(long) * 8)
#define NBITS(x) ((((x)-1)/BITS_PER_LONG)+1)
#define OFF(x)  ((x)%BITS_PER_LONG)
#define BIT(x)  (1UL<<OFF(x))
#define LONG(x) ((x)/BITS_PER_LONG)
#define test_bit(bit, array)    ((array[LONG(bit)] >> OFF(bit)) & 1)
#define FIRST_WORD_MASK(start) (~0UL << ((start) % BITS_PER_LONG))
#define LAST_WORD_MASK(nr) ((nr) % BITS_PER_LONG) ? (1UL << ((nr) % BITS_PER_LONG))-1 : ~0UL

void set_bit(unsigned long *map, int start, int nr)
{
        unsigned long *p = map + LONG(start);
        const int size = start + nr;
        int bits_to_set = BITS_PER_LONG - (start % BITS_PER_LONG);
        unsigned long mask_to_set = FIRST_WORD_MASK(start);

        while (nr - bits_to_set >= 0) {
                *p |= mask_to_set;
                nr -= bits_to_set;
                bits_to_set = BITS_PER_LONG;
                mask_to_set = ~0UL;
                p++;
        }
        if (nr) {
                mask_to_set &= LAST_WORD_MASK(size);
                *p |= mask_to_set;
        }

}

static unsigned long bitmap[NBITS(100)];
void printbitmap(int start, int nr)
{
        int i;
        for (i = start; i < start + nr; i++) {
                printf("%c", test_bit(i, bitmap) ? '1' : '0');
        }
        printf("\n");
}

int main(int argc, char *argv[])
{
        set_bit(bitmap, 10, 50);
        printbitmap(0, 100);

        return 0;
}