math.bitwise: remove duplicate logic in bitfield.
math.bitwise: remove duplicate logic in bitfield.

mrjbq7/factor,bpollack/factor,tgunr/factor,bpollack/factor,factor/factor,bpollack/factor,bpollack/factor,bpollack/factor,mrjbq7/factor,factor/factor,bpollack/factor,tgunr/factor,factor/factor,tgunr/factor,mrjbq7/factor,tgunr/factor,mrjbq7/factor,mrjbq7/factor,factor/factor,factor/factor,bpollack/factor,factor/factor,mrjbq7/factor,tgunr/factor,tgunr/factor