Is this valid C code?

Question

Possible duplicate:
What does the code do?

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 C code? If so, what is he trying to achieve and why would someone do something like this above?

Answer 1

It's called a Duff device, and you can read about it on wikipedia .

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void memcpy(char* dst, char* src, size_t count)
{
   begin:
     if (count-- == 0) return;
     *(dst++) = *(src++);
     goto begin;
}

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Answer 2

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Answer 3

Mandatory link to Duff Device on Wikipedia .