Quote from: Peter R on April 20, 2015, 11:05:11 PM

Quote from: Geremia on April 20, 2015, 10:50:42 PM

Quote from: solex on April 20, 2015, 07:16:33 PM

It seems obvious that reversible computing is the future for Bitcoin mining ASICs, and could be the first major commercial application of the technology.

From the Reddit page you linked: "No. Hashing by definition is irreversible and results in loss of information and therefore increased entropy."

It's irreversible because the normal circuit for SHA256d discards information (and thus requires an energy input to move in the forward direction). For example, we hash the 640 bit blockheader to get a 256 bit digest; there's no way to work backwards with only 256 bits to reconstruct the 640 bit input (the output contains less information than the input). But I don't see why there wouldn't be another circuit that performs the hash function in a reversible way, by tracking all the information that is normally discarded. This circuit would output the hash value PLUS enough of other information that one could work backwards to reconstruct the inputs.

Yes, that's what I was thinking. The final hash is irreversible, but not if the results of each step are known. The efficiency is gained by recycling logic gate inputs as they occur. Certainly a challenging design problem though.