Listing 2 Translating two characters back into 13-bit values

#define BASE 91          /* # possible output chars */
#define FIRST_CODE '!'   /* lowest output character */
#define BASEVAL(c) ((c)-FIRST_CODE)
...
  int t = getcode();         /* get next valid char */
  int u = getcode();         /* get next valid char */
  return BASEVAL(t) * BASE + BASEVAL(u);

/* End of File */