What is the minimum power requirement to preform a computation? The answer is none, if the computation is reversible. So computing `f`(`a`, `b`) ≝ `a` + `b` consumes energy because the loss of information must be dissipated as heat. However, computing `g`(`a`, `b`) ≝ (`a` + `b`, `a` − `b`) could be done without consuming any energy because the inputs can be recomputed from the output. And furthermore all computation can be turned into reversable computation by making a copy of the input in the output.

Of course this is a bit strange because the result of `g` contains more information that the result of `f`. There is something strange going on between information, entropy, computation, and energy that I don’t really understand.

The real energy cost seems to be in initializing the input to the values you want. Setting registers is not a reversible process.