--------------------------------------------------------------------------------- Title       : Parallel-prefix AND-OR structure for end-around carry-- Project     : VHDL Library of Arithmetic Units--------------------------------------------------------------------------------- File        : PrefixAndOrCendaround.vhd-- Author      : Reto Zimmermann  <zimmi@iis.ee.ethz.ch>-- 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)--   - carry-out (CO) independent of carry-in (for end-around carry adders)-------------------------------------------------------------------------------library ieee;use ieee.std_logic_1164.all;library arith_lib;use arith_lib.arith_lib.all;use arith_lib.arith_utils.all;-------------------------------------------------------------------------------entity PrefixAndOrCendaround is  generic (width : integer := 8;	-- word width	   speed : integer := 2);	-- 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        CO : out std_logic);  		-- carry outend PrefixAndOrCendaround;-------------------------------------------------------------------------------architecture Structural of PrefixAndOrCendaround is   signal GT, PT : std_logic_vector(width-1 downto 0);  -- gen./prop. tempbegin  -- normal prefix calculation  prefix : PrefixAndOr    generic map (width, speed)    port map (GI, PI, GT, PT);  -- carry-out  CO <= GT(width-1);  -- additional prefix calculation level for fast carry-in  GO <= GT or (PT and (width-1 downto 0 => CI));  PO <= PT;end Structural;-------------------------------------------------------------------------------