bug: bits.ToBinary create unnecessary constraints for constant inputs

[ivokub]

I see. So, If you don't like the idea of a generic solution, For now I'd recommend handling constant inputs in ToBinary explicitly. There are some practical examples that shows ToBinary may be called with a constant input, while the programmer cannot notice it. (the call is done inside another function) The current Implementation of ToBinary creates around 250 constraints for a constant input, while no constraints are needed.

Originally posted by @aybehrouz in #659 (comment)