Bit Operation (Modify Bit Data)

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

#define BYTETOBINARYPATTERN "%d%d%d%d%d%d%d%d"

#define BYTETOBINARY(byte) \
    (byte & 0x80 ? 1 : 0), \
    (byte & 0x40 ? 1 : 0), \
    (byte & 0x20 ? 1 : 0), \
    (byte & 0x10 ? 1 : 0), \
    (byte & 0x08 ? 1 : 0), \
    (byte & 0x04 ? 1 : 0), \
    (byte & 0x02 ? 1 : 0), \
    (byte & 0x01 ? 1 : 0)

#define PRINTBIN(x) printf(BYTETOBINARYPATTERN, BYTETOBINARY(x));

void setlsbs(unsigned char *p, unsigned char b0);
unsigned char getlsbs(unsigned char *p);


int main(int argc, char **argv)
{
    int seed;
    int i;
    unsigned char p[8];
    unsigned char byte0 = random()%256;    
    unsigned char return_val;

    sscanf(argv[1],"%d",&seed);
    srandom(seed);
    
    for(i = 0; i<8;i++)
    {
        p[i] = random()%256;
    }
    
    for(i = 0; i<8; i++)
    {
        printf("p[%d] = %d ",i,p[i]);
        printf("binary format: "); PRINTBIN(p[i]); printf("\n");        
    }

    printf("byte0 = %d ",byte0);
    printf("binary format: "); PRINTBIN(byte0); printf("\n");    

    setlsbs(p,byte0);

    for(i = 0; i<8; i++)
    {
        printf("p[%d] = %d ",i,p[i]);
        printf("binary format: "); PRINTBIN(p[i]); printf("\n");        
    }

    return_val = getlsbs(p);

    printf("Return value of the call to getlsbs(): %d ", return_val);    
    printf("binary format: "); PRINTBIN(return_val); printf("\n");    

    return 0;
}



void setlsbs(unsigned char *p, unsigned char b0)
{
    int i;
    int n[8];
    n[0]  = (b0 & 0x01) == 0x01 ? 1:0;
    n[1]  = (b0 & 0x02) == 0x02 ? 1:0;
    n[2]  = (b0 & 0x04) == 0x04 ? 1:0;
    n[3]  = (b0 & 0x08) == 0x08 ? 1:0;
    n[4]  = (b0 & 0x10) == 0x10 ? 1:0;
    n[5]  = (b0 & 0x20) == 0x20 ? 1:0;
    n[6]  = (b0 & 0x40) == 0x40 ? 1:0;
    n[7]  = (b0 & 0x80) == 0x80 ? 1:0;
    
    for(i = 0; i<8;i++)
    {
        /* modify the least significant bit of the byte */
        int index = 1<<0; 
        if(n[i])
        {
            p[i] |= index;
        }
        else
        {
            p[i] &= ~index;        
        }
    }    
}

unsigned char getlsbs(unsigned char *p)
{
    unsigned char ret_val = 0;
    int i;
    int temp;
    
    for(i = 0; i<8 ;i++)
    {
        temp = ( (p[i] & 0x01) == 0x01 ? pow(2,i):0 );
        ret_val += temp;        
    }

    return ret_val;        
}