alt Hacker NewsIt'll be different gates on the transistor for the different bits, and you power only one set depending on which bit of the result you wish to calculate.
Some would call it a multi-gate transistor, whilst others would call it multiple transistors in a row...
That, or a resistor ladder with 4 bit branches connected to a single gate, possibly with a capacitor in between, representing the binary state as an analogue voltage, i.e. an analogue-binary computer. If it works for flash memory it could work for this application as well.