Given a number n, print all primes smaller than or equal to n. It is also given that n is a small number.

Given a number n, print all primes smaller than or equal to n. It is also given that n is a small number.
For example, if n is 9 the output should be “2, 3, 5, 7″. If n is 18, the output should be “2, 3, 5, 7, 11, 13, 17″.

#include<stdio.h>

#include<malloc.h>

#include<math.h>

void unsetBit(char *b,int i){

    int blk=(i-1)/8;

    int shift=((i-1)%8);

    b[blk] &= ~(1<<shift);

}

int bitStatus(char *b,int i){

    int k,t,blk=(i-1)/8;

    int shift=((i-1)%8);

    k=b[blk]&(1<<shift);

    t=(k!=0)?(blk*8+(int)log2((double)k)+1):0;

    return t;

}

int main(){

    int n,nb,i,j,k;

    printf("\n Enter range of numbers = ");

    scanf("%d",&n);

    nb=(int)ceil((double)n/8.0);

    char *b=malloc(nb);

    printf("# bytes required = %d\n",nb);

    for(i=0;i<nb;b[i++]=0xFF);

    for(i=2;i<=sqrt(n);i++){

        if(bitStatus(b,i) != 0){

            for(j=i*i;j<=n;j+=i){

                unsetBit(b,j);

            }

        }

    }

    printf("\n");

    for(i=2;i<=n;i++){

        k=bitStatus(b,i);

        if(k!=0)

            printf("%5d",k);   

    }

    printf("\n");

    return 0;

}

//end