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[QUOTE="eliascm, post: 4029914, member: 54727"]
[b]Replacing "whens"[/b]

The code below does essentially what you are trying to do.  The function num_bits is in a package I wrote (vhdl_lib_2.arithmetic_pkg).

--=====================================================================
library ieee;
use ieee.std_logic_1164.all;
--=====================================================================
package m_to_n_mux_pkg is

constant mux_in_width   : positive := 256;       -- m
  constant mux_out_width  : positive := 9;         -- n

type vec_array is array(mux_in_width - 1 downto 0) of std_logic_vector(mux_out_width - 1 downto 0);

component m_to_n_mux
    port( sel     : in  std_logic_vector;
					mux_in  : in  vec_array;
          mux_out : out std_logic_vector(mux_out_width - 1 downto 0)
				);
  end component;

end m_to_n_mux_pkg;
--=====================================================================
library ieee;
	use ieee.std_logic_1164.all;
	use ieee.numeric_std.all;
library vhdl_lib_2;
	use vhdl_lib_2.arithmetic_pkg.all;
use work.m_to_n_mux_pkg.all;
--=====================================================================
--The num_bits function returns the minimum number of bits required to represent a specified number
-- of states using binary encoding.  For example: num_bits(5) = 3, num_bits(8) = 3, num_bits(9) = 4
-----------------------------------------------------------------------
entity m_to_n_mux is
  port( sel     : in  std_logic_vector(num_bits(mux_in_width) - 1 downt to 0);
				mux_in  : in  vec_array;
        mux_out : out std_logic_vector(mux_out_width - 1 downto 0)
			);
end m_to_n_mux;

architecture arch_mux of m_to_n_mux is

begin
  pmux : process(mux_in, sel)
	begin
    mux_out <= mux_in(to_integer(unsigned(sel)));
	end process;
end arch_mux;
[/QUOTE]

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