This program extracts k bits from given position say p

Logic:
1) right shift the number by p-1
2)set k bits

Do and of 1 & 2

Same question can be asked to extract from say p to k
then p =p but k = k-p +1

Implementation:

#include <stdio.h>
#define MAX_BITS sizeof(int) * 8
 
void display_binary(int num)
{
    int i =0;
    for(i = MAX_BITS -1; i>=0;i--)
    {
        if( num & (1 <<i))
           printf("1");
        else
           printf("0");
    }
}

int extract_k_bits(int num, int k, int p)
{
    return ( (num >> (p - 1)) & ( (1 << k) -1));
}

int main()
{
  int num,k,p;
  
  printf("\n Enter the number: ");
  scanf("%d", &num);
  
  printf("\n Enter the number of bit: ");
  scanf("%d", &k);
  
  printf("\n Enter the starting bit: ");
  scanf("%d", &p);
  
  printf("\n Original number is: %d  binary: ", num);
  display_binary(num);
  
  int res = extract_k_bits(num, k, p);
  printf("\n The result is: %d binary: ", res);
  display_binary(res);
  
  return 0;
}

Output:

Enter the number: 171

Enter the number of bit: 5

Enter the starting bit: 2

Original number is: 171  binary: 00000000000000000000000010101011
The result is: 21 binary: 00000000000000000000000000010101

Categories: Data Structure and Algorithm