有名どころで Duff's device.
http://www.tuxedo.org/~esr/jargon/html/entry/Duff's-device.html
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);
}
理解した時に世の中にはキチガイがいるもんだと実感した。