Neal R. Wagner

C Code to Simulate the Rotor Puzzle

Here is a portion of a C program that will simulate the puzzle. (This is just a C function that carries out a puzzle step. One would need a main function and other C code to run a simulation.)


#define ISODD(n) ((n)&1)
#define ISEVEN(n) (!((n)&1))
#define MOD(x,y) (((x) % (y)) >= 0 ? (x)%(y) : ((x)%(y)) + (y))
#define M(i,j) (MOD(((i) + orient*(j)), 6))
#define EVENODD(i) (orient == 1 ? ISEVEN(i) : ISODD(i))
long orient; /* heading right or left, orient = 1 or -1 */
/* T: takes an input puzzle configuration as the array W[6],
 *    an input puzzle orientation D, and an input roller
 *    insertion point In.  Produces a new configurataion W[6]
 *    and output exit hole Out.
 *       W[6]: gives orientation of each rotor arm, 0 to 5
 *       D:    gives orientation of whole puzzle, 0 to 5
 *       In:   gives hole where roller is inserted, D-1, D, or D+1
 *       Out:  gives hole roller exits, D+2, D+3, or D+4
 *       orient: global that keeps track of whether roller is
 *               heading left (-1) or right (1)
 */
void T(long W[6], long D, long In, long *Out)
{
   orient = 1;
   if (In == D) {
      if ( ISEVEN (M(D, W[D])) ) orient = 1;
      else orient = -1;
      W[D] = M( W[D], 1);
      /* head to W[D+1]  */
      if ( EVENODD( M(D, W[ M(D,1)])) )
         W[ M(D, 1) ] = M( W[ M(D, 1) ], -1);
      else
         W[ M(D, 1) ] = M( W[ M(D, 1) ], -2);
   }
   else if (In == M(D, 1)) {
      orient = 1;
      /* into W[D+1]  */
      if ( ISODD( M(D, W[ M(D,1)])) )
         W[ M(D, 1) ] = M( W[ M(D, 1) ],  1);
      else
         W[ M(D, 1) ] = M( W[ M(D, 1) ],  2);
   }
   else if (In == M(D, -1)) {
      orient = -1;
      /* into W[D+orient*1], i.e., into W[D-1]  */
      if ( ISEVEN( M(D, W[ M(D,1)])) )
         W[ M(D, 1) ] = M( W[ M(D, 1) ],  1);
      else
         W[ M(D, 1) ] = M( W[ M(D, 1) ],  2); 
   }
   /*****  else  ERROR */
   /* head to W[D+orient*2]  */
   if ( EVENODD( M(D, W[ M(D,2)])) ) {
      W[ M(D, 2) ] = M( W[ M(D, 2) ],  1);
      *Out = M(D, 2);
   }
   else {
      W[ M(D, 2) ] = M( W[ M(D, 2) ], -1);
      /* head to W[D+orient*3] */
      if ( EVENODD( M(D, W[ M(D, 3) ] )) )
         W[ M(D, 3) ] = M( W[ M(D, 3) ],  2);
      else  
         W[ M(D, 3) ] = M( W[ M(D, 3) ],  1);
      *Out = M(D, 3);
   }
}