资料来源 : Free On-Line Dictionary of Computing

Duff's device
     
        The most dramatic use yet seen of {fall through} in {C},
        invented by Tom Duff when he was at Lucasfilm.  Trying to
        {bum} all the instructions he could out of an inner loop that
        copied data serially onto an output port, he decided to unroll
        it.  He then realised that the unrolled version could be
        implemented by *interlacing* the structures of a switch and a
        loop:
     
          register n = (count + 7) / 8;      /* count > 0 assumed */
     
          switch (count % 8)
          {
          case 0:        do {  *to = *from++;
          case 7:              *to = *from++;
          case 6:              *to = *from++;
          case 5:              *to = *from++;
          case 4:              *to = *from++;
          case 3:              *to = *from++;
          case 2:              *to = *from++;
          case 1:              *to = *from++;
                             } while (--n > 0);
          }
     
        Shocking though it appears to all who encounter it for the
        first time, the device is actually perfectly valid, legal C.
        C's default {fall through} in case statements has long been
        its most controversial single feature; Duff observed that
        "This code forms some sort of argument in that debate, but I'm
        not sure whether it's for or against."
     
        [For maximal obscurity, the outermost pair of braces above
        could be actually be removed - {GLS}]
     
        [{Jargon File}]
     
        (2001-06-22)