Question

Say I have 2 std_logic_vectors:

inputA : std_logic_vector(31 downto 0)
inputB:  std_logic_vector(31 downto 0)

How do I shift inputA by inputB using concatenation?

I know how to shift left or right by 1 place but can’t figure out how to shift N places to the right (or left).
Note: this is a clockless circuit, and can’t use standard vhdl shift operators.

Other techniques or ideas other than concatenation would be appreciated as well.

Answer 1

I prefer wjl’s approach, but given you asked specifically for a method using concatenation, try this:

function variable_shift(i : std_logic_vector, num_bits : integer) 
   return std_logic_vector is
   constant zeros : std_logic_vector(num_bits-1 downto 0) := (others => '0');
begin
   return i(i'high-num_bits downto i'low) & zeros;
end function;

(It could be written to take a second std_logic_vector for the num_bits parameter, but as it’s fundamentally a number, I’d always use a number-based type for it)