Question

C programming lab:

Description:
In this lab you will write a program that will contain two functions, setlsbs() and getlsbs(). These functions will use bitwise operators to embed and extract "hidden" bits in a character array.

Write a program to test your functions as follows:

• Obtain a random number seed from the command line of your program using command line arguments.

• Initialize an array p of 8 unsigned char with random numbers from 0 to 255

• Initialize a separate unsigned character byte0 with a random number.

• Print the values in the array p as well as the value for byte0.

  • Print the values in decimal format as well as binary format (use macros defined below)

• Call setlsbs() using p and byte0 as parameters

• After the call to setlsbs() is completed, print the modified values of the array p.

  • Print the values in decimal format as well as binary format (use macros defined below)

• Use the modified array p as a parameter to getlsbs()

• Print the return value of the call to getlsbs(). The returned value should match the original value for byte0

  • Print the value in decimal format as well as binary format (use macros defined below)

Background Preparation:

• Review bitwise operators (Section 2.9 in textbook).

Specifications:
Your first function:

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

will take as parameters, an array p of eight bytes (unsigned char) and a byte byte0. It will replace the least significant bits (LSBs) of p by the bits of byte0. In other words, if the binary representation of byte0 is b₇b₆b₅b₄b₃b₂b₁b₀, you should replace the LSB of p[0] by b₀, the LSB of p[1] by b₁, ... , and the LSB of p[7] by b₇.

Your second function:

unsigned char getlsbs(unsigned char *p)

will take an array p of eight bytes (unsigned char) and return a byte byte0 which is created by combining the LSBs of p. That is, your function should combine the least significant bits b_i of p[i] to return a byte b₇b₆b₅b₄b₃b₂b₁b₀.

Macros:
You may use the following macros to print the binary representation of unsigned character variables:

#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));

You can use the macros in a manner similar to the code below:

unsigned char num =173;

PRINTBIN(num); printf("\n");

Answer 1

Do like and comment if you have any queries.

Note:

Used and updated the code given in the question and used the same variable names as requested

Code to copy:

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

   //funtion prints array p in binary format
   void print_Binary_parray(unsigned char *p){
   int i;
   for(i=0;i<8;i++){
       PRINTBIN(p[i]);
       printf("\n");
   }
   }
   //funtion prints array p in decimal format
   void print_Decimal_parray(unsigned char *p){
   int i;
   for(i=0;i<8;i++){
       printf("%u ",p[i]);
   }
   printf("\n");
   }
   //funtion sets the LSB of each element in array p wiht byte_0 value
   void setlsbs(unsigned char *p, unsigned char b0){
       unsigned char p_Tempy;
       unsigned char tst = 0x01;
       int i;
       int v;
  
       for(i=0;i<8;i++){
           p_Tempy = b0;
           //checking byte_0 bit is set at a particular position i
           v = p_Tempy&tst?1:0;
           //if the byte_0 bit is set in position i
           //set the p[i] LSB
           //else unset p[i] LSB
           if(v){
               p[i] = p[i] | 0x01;
           }else{
               p[i] = p[i] & 0xFE;
           }
           //moving the position decider of byte_0 to right
           tst = tst<<1;
       }
  
   }
   //funtion gets LSB bits of elements in arra p and append it to result
   unsigned char getlsbs(unsigned char *p){
   int i;
   unsigned char res=0;
   for(i=7;i>=0;i--){
       //appending res with LSB of p[i]
       //the shift right the result
       res=(res|(p[i]&0x01));
       if(i!=0)
       res=res<<1;
   }
   return res;
   }

   int main(){
   int i;
   int max=255;
   int min=0;
   //setting the seed of random number generation
   srand(1);
  
   unsigned char byte_0 ;
   unsigned char p[8];
   //Initialize an array p of 8 unsigned char with random numbers from 0 to 255
   for(i=0;i<8;i++){
       p[i]=(rand() % (max - min + 1)) + min;
   }
   //Initialize a separate unsigned character byte_0 with a random number.
   byte_0 = rand();
  
   //Printing the values in the array p as well as the value for byte_0. in decimal format
   printf("\nValue of array P in decimal format= ");
   print_Decimal_parray(p);
   printf("\nValue of byte_0 in decimal format = %u\n",byte_0);
  
   //Printing the values in binary format
   printf("\nValue of array P in binary format\n");
   print_Binary_parray(p);
   printf("\nValue of byte_0 in binary format =");
   PRINTBIN(byte_0);
  
   //Calling setlsbs() using p and byte_0 as parameters
   setlsbs(p,byte_0);
  
   //printing modified values of array p in decimal
   printf("\nPrinting P after setting LSB in decimal = ");
   print_Decimal_parray(p);
  
   //print the modified values of the array p. in binary
   printf("\nPrinting P after setting LSB in binary\n");
   print_Binary_parray(p);
  
   //calling getlsb() with porameter p
   unsigned char byte_0_new = getlsbs(p);

   //Returned value of byte_0 from getlsb() in decimal format
   printf("\nValue of returned byte_0 in decimal format = %u\n",byte_0_new);
  
   //Returned value of byte_0 from getlsb() in binary format
   printf("\nValue of returned byte_0 in binary format =");
   PRINTBIN(byte_0_new);
   return 0;
   }

Output Screenshot:

Code Screenshot: