src/pre_norm_sqrt.vhd

   1 -------------------------------------------------------------------------------
   2 -- Description: pre-normalization entity for the square-root unit
   3 -- See COPYRIGHT.jop
   4
   5 library ieee ;
   6 use ieee.std_logic_1164.all;
   7 use ieee.std_logic_unsigned.all;
   8 use ieee.std_logic_misc.all;
   9
  10 library work;
  11 use work.fpupack.all;
  12
  13 entity pre_norm_sqrt is
  14         port(
  15                          clk_i                  : in std_logic;
  16                          opa_i                  : in std_logic_vector(FP_WIDTH-1 downto 0);
  17                          fracta_52_o    : out std_logic_vector(2*(FRAC_WIDTH+3)-1 downto 0);
  18                          exp_o                  : out std_logic_vector(EXP_WIDTH-1 downto 0)
  19                 );
  20 end pre_norm_sqrt;
  21
  22 architecture rtl of pre_norm_sqrt is
  23
  24 signal s_expa : std_logic_vector(EXP_WIDTH-1 downto 0);
  25 signal s_exp_o, s_exp_tem : std_logic_vector(EXP_WIDTH downto 0);
  26 signal s_fracta : std_logic_vector(FRAC_WIDTH-1 downto 0);
  27 signal s_fracta_24 : std_logic_vector(FRAC_WIDTH downto 0);
  28 signal s_fracta_52_o, s_fracta1_52_o, s_fracta2_52_o : std_logic_vector(2*(FRAC_WIDTH+3)-1 downto 0);
  29 signal s_sqr_zeros_o : std_logic_vector(5 downto 0);
  30
  31
  32 signal s_opa_dn : std_logic;
  33
  34 begin
  35
  36         s_expa <= opa_i(FP_WIDTH-2 downto FRAC_WIDTH);
  37         s_fracta <= opa_i(FRAC_WIDTH-1 downto 0);
  38
  39
  40         exp_o <= s_exp_o(EXP_WIDTH-1 downto 0);
  41         fracta_52_o <= s_fracta_52_o;
  42
  43         -- opa or opb is denormalized
  44         s_opa_dn <= not or_reduce(s_expa);
  45
  46         s_fracta_24 <= (not s_opa_dn) & s_fracta;
  47
  48         -- count leading zeros
  49         s_sqr_zeros_o <= count_l_zeros(s_fracta_24 );
  50
  51         -- adjust the exponent
  52         s_exp_tem <= ("0"&s_expa)+"001111111" - ("000"&s_sqr_zeros_o);
  53
  54         process(clk_i)
  55         begin
  56                 if rising_edge(clk_i) then
  57                         if or_reduce(opa_i(30 downto 0))='1' then
  58                                 s_exp_o <= ("0"&s_exp_tem(EXP_WIDTH downto 1));
  59                         else
  60                                 s_exp_o <= "000000000";
  61                         end if;
  62                 end if;
  63         end process;
  64
  65         -- left-shift the radicand
  66         s_fracta1_52_o <= shl(s_fracta_24, s_sqr_zeros_o) & "0000000000000000000000000000";
  67         s_fracta2_52_o <= '0' & shl(s_fracta_24, s_sqr_zeros_o) & "000000000000000000000000000";
  68
  69         s_fracta_52_o <= s_fracta1_52_o when s_expa(0)='0' else s_fracta2_52_o;
  70
  71 end rtl;