Subversion Repositories fpu100

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

--

-- Project:     <Floating Point Unit Core>

--      

-- Description: post-normalization entity for the addition/subtraction unit

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

--

--                              100101011010011100100

--                              110000111011100100000

--                              100000111011000101101

--                              100010111100101111001

--                              110000111011101101001

--                              010000001011101001010

--                              110100111001001100001

--                              110111010000001100111

--                              110110111110001011101

--                              101110110010111101000

--                              100000010111000000000

--

--      Author:          Jidan Al-eryani 

--      E-mail:          jidan@gmx.net

--

--  Copyright (C) 2006

--

--      This source file may be used and distributed without        

--      restriction provided that this copyright statement is not   

--      removed from the file and that any derivative work contains 

--      the original copyright notice and the associated disclaimer.

--                                                           

--              THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY     

--      EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED   

--      TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS   

--      FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL THE AUTHOR      

--      OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,         

--      INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES    

--      (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE   

--      GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR        

--      BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF  

--      LIABILITY, WHETHER IN  CONTRACT, STRICT LIABILITY, OR TORT  

--      (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT  

--      OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE         

--      POSSIBILITY OF SUCH DAMAGE. 

--

library ieee ;

use ieee.std_logic_1164.all;

use ieee.std_logic_unsigned.all;

use ieee.std_logic_misc.all;

library work;

use work.fpupack.all;

entity post_norm_addsub is

        port(

                        clk_i                   : in std_logic;

                        opa_i                   : in std_logic_vector(FP_WIDTH-1 downto 0);

                        opb_i                   : in std_logic_vector(FP_WIDTH-1 downto 0);

                        fract_28_i              : in std_logic_vector(FRAC_WIDTH+4 downto 0);    -- carry(1) & hidden(1) & fraction(23) & guard(1) & round(1) & sticky(1)

                        exp_i                   : in std_logic_vector(EXP_WIDTH-1 downto 0);

                        sign_i                  : in std_logic;

                        fpu_op_i                : in std_logic;

                        rmode_i                 : in std_logic_vector(1 downto 0);

                        output_o                : out std_logic_vector(FP_WIDTH-1 downto 0);

                        ine_o                   : out std_logic

                );

end post_norm_addsub;

architecture rtl of post_norm_addsub is

signal s_opa_i, s_opb_i         : std_logic_vector(FP_WIDTH-1 downto 0);

signal s_fract_28_i                     : std_logic_vector(FRAC_WIDTH+4 downto 0);

signal s_exp_i                          : std_logic_vector(EXP_WIDTH-1 downto 0);

signal s_sign_i                         : std_logic;

signal s_fpu_op_i                       : std_logic;

signal s_rmode_i                        : std_logic_vector(1 downto 0);

signal s_output_o                       : std_logic_vector(FP_WIDTH-1 downto 0);

signal s_ine_o                          : std_logic;

signal s_overflow                       : std_logic;

signal s_zeros, s_shr1, s_shl1 : std_logic_vector(5 downto 0);

signal s_shr2, s_carry : std_logic;

signal s_exp10: std_logic_vector(9 downto 0);

signal s_expo9_1, s_expo9_2, s_expo9_3: std_logic_vector(EXP_WIDTH downto 0);

signal s_fracto28_1, s_fracto28_2, s_fracto28_rnd : std_logic_vector(FRAC_WIDTH+4 downto 0);

signal s_roundup : std_logic;

signal s_sticky : std_logic;

signal s_zero_fract : std_logic;

signal s_lost : std_logic;

signal s_infa, s_infb : std_logic;

signal s_nan_in, s_nan_op, s_nan_a, s_nan_b, s_nan_sign : std_logic;

begin

        -- Input Register

        --process(clk_i)

        --begin

        --      if rising_edge(clk_i) then      

                        s_opa_i <= opa_i;

                        s_opb_i <= opb_i;

                        s_fract_28_i <= fract_28_i;

                        s_exp_i <= exp_i;

                        s_sign_i <= sign_i;

                        s_fpu_op_i <= fpu_op_i;

                        s_rmode_i <= rmode_i;

        --      end if;

        --end process;  

        -- Output Register

        process(clk_i)

        begin

                if rising_edge(clk_i) then

                        output_o <= s_output_o;

                        ine_o <= s_ine_o;

                end if;

        end process;

        --*** Stage 1 ****

        -- figure out the output exponent and howmuch the fraction has to be shiftd right/left

        s_carry <= s_fract_28_i(27);

        s_zeros <= count_l_zeros(s_fract_28_i(26 downto 0)) when s_fract_28_i(27)='0' else "000000";

        s_exp10 <= ("00"&s_exp_i) + ("000000000"&s_carry) - ("0000"&s_zeros); -- negative flag & large flag & exp               

        process(clk_i)

        begin

        if rising_edge(clk_i) then

                        if s_exp10(9)='1' or s_exp10="0000000000" then

                                s_shr1 <= (others =>'0');

                                if or_reduce(s_exp_i)/='0' then

                                        s_shl1 <= s_exp_i(5 downto 0) - "000001";

                                else

                                        s_shl1 <= "000000";

                                end if;

                                s_expo9_1 <= "000000001";

                        elsif s_exp10(8)='1' then

                                s_shr1 <= (others =>'0');

                                s_shl1 <= (others =>'0');

                                s_expo9_1 <= "011111111";

                        else

                                s_shr1 <= ("00000"&s_carry);

                                s_shl1 <= s_zeros;

                                s_expo9_1 <= s_exp10(8 downto 0);

                        end if;

        end if;

        end process;

---

        -- *** Stage 2 ***

        -- Shifting the fraction and rounding

        process(clk_i)

        begin

                if rising_edge(clk_i) then

                        if s_shr1 /= "000000" then

                                s_fracto28_1 <= shr(s_fract_28_i, s_shr1);

                        else

                                s_fracto28_1 <= shl(s_fract_28_i, s_shl1);

                        end if;

                end if;

        end process;

        s_expo9_2 <= s_expo9_1 - "000000001" when s_fracto28_1(27 downto 26)="00" else s_expo9_1;

        -- round

        s_sticky <='1' when s_fracto28_1(0)='1' or (s_fract_28_i(0) and s_fract_28_i(27))='1' else '0'; --check last bit, before and after right-shift

        s_roundup <= s_fracto28_1(2) and ((s_fracto28_1(1) or s_sticky)or s_fracto28_1(3)) when s_rmode_i="00" else -- round to nearset even

                                                         (s_fracto28_1(2) or s_fracto28_1(1) or s_sticky) and (not s_sign_i) when s_rmode_i="10" else -- round up

                                                         (s_fracto28_1(2) or s_fracto28_1(1) or s_sticky) and (s_sign_i) when s_rmode_i="11" else -- round down

                                                         '0'; -- round to zero(truncate = no rounding)

        s_fracto28_rnd <= s_fracto28_1 + "0000000000000000000000001000" when s_roundup='1' else s_fracto28_1;

        -- ***Stage 3***

        -- right-shift after rounding (if necessary)

        s_shr2 <= s_fracto28_rnd(27);

        s_expo9_3 <= s_expo9_2 + "000000001" when s_shr2='1' and s_expo9_2 /= "011111111" else s_expo9_2;

        s_fracto28_2 <= ("0"&s_fracto28_rnd(27 downto 1)) when s_shr2='1' else s_fracto28_rnd;

-----

        s_infa <= '1' when s_opa_i(30 downto 23)="11111111"  else '0';

        s_infb <= '1' when s_opb_i(30 downto 23)="11111111"  else '0';

        s_nan_a <= '1' when (s_infa='1' and or_reduce (s_opa_i(22 downto 0))='1') else '0';

        s_nan_b <= '1' when (s_infb='1' and or_reduce (s_opb_i(22 downto 0))='1') else '0';

        s_nan_in <= '1' when s_nan_a='1' or  s_nan_b='1' else '0';

        s_nan_op <= '1' when (s_infa and s_infb)='1' and (s_opa_i(31) xor (s_fpu_op_i xor s_opb_i(31)) )='1' else '0'; -- inf-inf=Nan

        s_nan_sign <= s_sign_i when (s_nan_a and s_nan_b)='1' else

                                                                s_opa_i(31) when s_nan_a='1' else

                                                                s_opb_i(31);

        -- check if result is inexact;

        s_lost <= (s_shr1(0) and s_fract_28_i(0)) or (s_shr2 and s_fracto28_rnd(0)) or or_reduce(s_fracto28_2(2 downto 0));

        s_ine_o <= '1' when (s_lost or s_overflow)='1' and (s_infa or s_infb)='0' else '0';

        s_overflow <='1' when s_expo9_3="011111111" and (s_infa or s_infb)='0' else '0';

        s_zero_fract <= '1' when s_zeros=27 and s_fract_28_i(27)='0' else '0'; -- '1' if fraction result is zero

        process(s_sign_i, s_expo9_3, s_fracto28_2, s_nan_in, s_nan_op, s_nan_sign, s_infa, s_infb, s_overflow, s_zero_fract)

        begin

                if (s_nan_in or s_nan_op)='1' then

                        s_output_o <= s_nan_sign & QNAN;

                elsif (s_infa or s_infb)='1' or s_overflow='1' then

                                s_output_o <= s_sign_i & INF;

                elsif s_zero_fract='1' then

                                s_output_o <= s_sign_i & ZERO_VECTOR;

                else

                                s_output_o <= s_sign_i & s_expo9_3(7 downto 0) & s_fracto28_2(25 downto 3);

                end if;

        end process;

end rtl;