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Is the above valid C code?
I was given this question in my college in a programming contest...
void duff(register char *to, register char *from, register int count)
  {
      register int n=(count+7)/8;
      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);
      }
  }

Is the above valid C code? If so, what is it trying to acheive and why would anyone do something like the above? 

@phresnel: Good job asking

possible duplicate of What does this C code do [Duff's device]?

I am sorry. I had seen this question on a puzzle site.

Yep, it's known as Duff's device.
As far as I can remember it was written by someone doing special effects for a movie (Star Wars or something like that).  It was written this way to get maximum performance.
But, would I suggest to write code like this: NO.
Keep your code readable!
