#if defined STEP_FULL
    index &= 0x03;                              /* Wrap at end of table */
#elif defined STEP_HALF
    index &= 0x07;                              /* Wrap at end of table */
#elif defined STEP_QUARTER
    index &= 0x0F;                              /* Wrap at end of table */
#elif STEP_SIXTH
    if (index > 23) index = 0;                  /* Wrap at end of table */
    if (index < 0)  index = 23;                 /* Wrap at end of table */
#else
#error One of STEP_FULL, STEP_HALF, STEP_QUARTER, STEP_SIXTH must be defined!
#endif