/* This is a table which will contain number of ones 
corrosponding to number value */ 
static int bits_in_char [256] ;           
   
   int bitcount (unsigned int n)
   {
      // works only for 32-bit ints
    
      return bits_in_char [n         & 0xffu]
          +  bits_in_char [(n >>  8) & 0xffu]
          +  bits_in_char [(n >> 16) & 0xffu]
          +  bits_in_char [(n >> 24) & 0xffu] ;
   }