In reply to tejasakulu:
Can you give us an example of a negative number you would like to see generated with only one bit set? I can only think of one: -32767.
Maybe you mean a negative number with the sign bit set and one other bit set. That would be 2 bits set. Neither -1 nor -1024 meet those constraints.
Or maybe you mean a negative number whose absolute value has only one bit set. Then both -1 and -1024 meet those constraints.