Assignments for vectors inequal in length

Basically, you drop the MSBs

-- Id: R.1
  function RESIZE (ARG: SIGNED; NEW_SIZE: NATURAL) return SIGNED;
  -- Result subtype: SIGNED(NEW_SIZE-1 downto 0)
  -- Result: Resizes the SIGNED vector ARG to the specified size.
  --         To create a larger vector, the new  bit positions
  --         are filled with the sign bit (ARG'LEFT). When truncating,
  --         the sign bit is retained along with the rightmost part.
  -- Id: R.2
  function RESIZE (ARG: UNSIGNED; NEW_SIZE: NATURAL) return UNSIGNED;
  -- Result subtype: UNSIGNED(NEW_SIZE-1 downto 0)
  -- Result: Resizes the UNSIGNED vector ARG to the specified size.
  --         To create a larger vector, the new  bit positions
  --         are filled with '0'. When truncating, the leftmost bits
  --         are dropped.