Parametrized Priority Encoder ((2**W) to W-Line)

priority_encoder.vhd

library ieee;
use ieee.std_logic_1164.all;
use ieee.numeric_std.all;
use ieee.math_real.all;

entity priority_encoder is
  generic (
    W: integer := 3
  );
  port (
    input  : in  std_logic_vector(2**W-1 downto 0);
    output : out std_logic_vector(W-1 downto 0);
    eout   : out std_ulogic
  );
end priority_encoder;

architecture logic of priority_encoder is

procedure PRI_ENC (
  signal input  : in  std_logic_vector;
  signal output : out std_logic_vector;
  signal eout   : out std_logic
) is
  constant W : integer := integer(ceil(log2(real(input'length))));
  variable highest : std_logic_vector(W-1 downto 0) := (others => '0');
  variable no_ones : std_logic := '1';
begin
  for i in input'reverse_range loop
    if (input(i) = '1') then
      highest := std_logic_vector(to_unsigned(i, W));
      no_ones := '0';
    end if;
  end loop;
  output <= highest;
  eout <= no_ones;
end procedure;

begin

PRI_ENC(input, output, eout);

end logic;

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