Question

For example, I have 3 counters (which I essentially want to represent as truth values (counter > 0 true; false otherwise). This leads to 2^3 = 8 permutations for my truth values as shown:

000
001
010
011
100
101
110
111

Then each permutation maps to a state. How do I convert these counters to a binary representation at the bit level, and then how would I use the binary representation in a switch structure to map to a state? (ex. 001 maps to “contains x” and 010 maps to “contains y”, and 011 would map to “contains x and y”. Will this all be portable to other operating systems as well?

Answer 1

One possibility is to define constants with the value for each bit corresponding to each counter:

#define CTR1_BIT 0x01
#define CTR2_BIT 0x02
#define CTR3_BIT 0x04

Then based on the counter values (zero or non-zero) set the bits. The | operator performs a bitwise logical OR operation (see this for more information). If ctr1 is nonzero, it just sets the lowest order bit in the variable state. If ctr2 is nonzero, it sets the second bit in state to a 1 and leaves other bits unchanged. etc.

   int state = 0;

   if ( ctr1 )
      state |= CTR1_BIT;
   if ( ctr2 )
      state |= CTR2_BIT;
   if ( ctr3 )
      state |= CTR3_BIT;

Then switch on the possible state values:

   switch ( state )
      {
      case 0x00:
         printf( "state 0\n" );
         break;
      case 0x01:
         printf( "state 1\n" );
         break;
      case 0x02:

         ...

      case 0x07:
         printf( "state 7\n" );
         break;
      default:
         printf( "Invalid state\n" );
         assert(0);
      }