4-Bit Subtractor

The entity subtractor_4bit has two inputs i_a and i_b of type std_logic_vector(3 downto 0), an output o_diff of type std_logic_vector(3 downto 0) and an output o_borrow of type std_logic.

Subtracts two 4-bit unsigned vectors (A - B). The result o_diff is 4 bits. The borrow o_borrow is '1' when A < B.