I suspect it's logically equivalent, but one bit wider in hardware. Binary 4x is left shift by 2, rather than 2x which is by one. Adding or subtracting in 2's

I suspect it's logically equivalent, but one bit wider in hardware. Binary 4x is left shift by 2, rather than 2x which is by one. Adding or subtracting in 2's compliment space is the same operation for the bits of the word.