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

-- Copyright (C) 2004 Arif Endro Nugroho

-- All rights reserved.

-- 

-- Redistribution and use in source and binary forms, with or without

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-- 1. Redistributions of source code must retain the above copyright

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-- THIS SOFTWARE IS PROVIDED BY ARIF ENDRO NUGROHO "AS IS" AND ANY EXPRESS

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

library IEEE;

use IEEE.STD_LOGIC_1164.ALL;

entity adder_12bit is

   port (

      addend_12bit  : in  bit_vector (11 downto 0);

      augend_12bit  : in  bit_vector (11 downto 0);

      adder12_output: out bit_vector (12 downto 0)  -- 13bit output

      );

end adder_12bit;

architecture structural of adder_12bit is

   component fulladder

      port (

      addend        : in   bit;

      augend        : in   bit;

      carry_in      : in   bit;

      sum           : out  bit;

      carry         : out  bit

      );

   end component;

-- internal signal

signal over12 : bit;

signal adder12_output_int : bit_vector (11 downto 0);

signal c00 : bit;

signal c01 : bit;

signal c02 : bit;

signal c03 : bit;

signal c04 : bit;

signal c05 : bit;

signal c06 : bit;

signal c07 : bit;

signal c08 : bit;

signal c09 : bit;

signal c10 : bit;

signal c11 : bit;

signal c12 : bit;

signal ov  : bit;

begin

c00                     <= '0';

over12                  <= (addend_12bit (11) xor augend_12bit (11));

ov                      <= ((adder12_output_int (11) and over12) or

                           (c12 and (not (over12))));

adder12_output(11 downto 00) <= adder12_output_int;

adder12_output(12)           <= ov;

fa11 : fulladder

   port map (

      addend     => addend_12bit(11),

      augend     => augend_12bit(11),

      carry_in   => c11,

      sum        => adder12_output_int(11),

      carry      => c12

      );

fa10 : fulladder

   port map (

      addend     => addend_12bit(10),

      augend     => augend_12bit(10),

      carry_in   => c10,

      sum        => adder12_output_int(10),

      carry      => c11

      );

fa09 : fulladder

   port map (

      addend     => addend_12bit(09),

      augend     => augend_12bit(09),

      carry_in   => c09,

      sum        => adder12_output_int(09),

      carry      => c10

      );

fa08 : fulladder

   port map (

      addend     => addend_12bit(08),

      augend     => augend_12bit(08),

      carry_in   => c08,

      sum        => adder12_output_int(08),

      carry      => c09

      );

fa07 : fulladder

   port map (

      addend     => addend_12bit(07),

      augend     => augend_12bit(07),

      carry_in   => c07,

      sum        => adder12_output_int(07),

      carry      => c08

      );

fa06 : fulladder

   port map (

      addend     => addend_12bit(06),

      augend     => augend_12bit(06),

      carry_in   => c06,

      sum        => adder12_output_int(06),

      carry      => c07

      );

fa05 : fulladder

   port map (

      addend     => addend_12bit(05),

      augend     => augend_12bit(05),

      carry_in   => c05,

      sum        => adder12_output_int(05),

      carry      => c06

      );

fa04 : fulladder

   port map (

      addend     => addend_12bit(04),

      augend     => augend_12bit(04),

      carry_in   => c04,

      sum        => adder12_output_int(04),

      carry      => c05

      );

fa03 : fulladder

   port map (

      addend     => addend_12bit(03),

      augend     => augend_12bit(03),

      carry_in   => c03,

      sum        => adder12_output_int(03),

      carry      => c04

      );

fa02 : fulladder

   port map (

      addend     => addend_12bit(02),

      augend     => augend_12bit(02),

      carry_in   => c02,

      sum        => adder12_output_int(02),

      carry      => c03

      );

fa01 : fulladder

   port map (

      addend     => addend_12bit(01),

      augend     => augend_12bit(01),

      carry_in   => c01,

      sum        => adder12_output_int(01),

      carry      => c02

      );

fa00 : fulladder

   port map (

      addend     => addend_12bit(00),

      augend     => augend_12bit(00),

      carry_in   => c00,

      sum        => adder12_output_int(00),

      carry      => c01

      );

end structural;