prefixandorcfast.vhd

Cadence的VHDL运算库包

-------------------------------------------------------------------------------
-- Title       : Parallel-prefix AND-OR structure with fast carry-in
-- Project     : VHDL Library of Arithmetic Units
-------------------------------------------------------------------------------
-- File        : PrefixAndOrCfast.vhd
-- Author      : Reto Zimmermann  <[e-mail]>
-- Company     : Integrated Systems Laboratory, ETH Zurich
-- Date        : 1997/11/04
-------------------------------------------------------------------------------
-- Copyright (c) 1998 Integrated Systems Laboratory, ETH Zurich
-------------------------------------------------------------------------------
-- Description :
-- Prefix AND-OR structure with
--   - fast carry-in (CI)
-------------------------------------------------------------------------------

library ieee;
use ieee.std_logic_1164.all;
library arith_lib;
use arith_lib.arith_lib.all;
use arith_lib.arith_utils.all;

-------------------------------------------------------------------------------

entity PrefixAndOrCfast is

  generic (width : positive := 8;	-- word width
	   speed : speedType := fast);	-- performance parameter

  port (GI, PI : in std_logic_vector(width-1 downto 0);  -- gen./prop. in
        CI : in std_logic;  		-- carry in
	GO, PO : out std_logic_vector(width-1 downto 0));  -- gen./prop. out

end PrefixAndOrCfast;

-------------------------------------------------------------------------------

architecture Structural of PrefixAndOrCfast is 

  signal CIT : std_logic_vector(width-1 downto 0);  -- carry in temp
  signal GT, PT : std_logic_vector(width-1 downto 0);  -- gen./prop. temp

begin

  -- normal prefix calculation
  prefix : PrefixAndOr
    generic map (width, speed)
    port map (GI, PI, GT, PT);

  -- additional prefix calculation level for fast carry-in
  CIT <= (others => CI);
  GO <= GT or (PT and CIT);

end Structural;

-------------------------------------------------------------------------------