library ieee;
use ieee.std_logic_1164.all;
use ieee.std_logic_arith.all;
use ieee.std_logic_unsigned.all;

package pkg_fp_exp is
  function min ( x, y : integer ) return integer;
  function max ( x, y : integer ) return integer;
  function fp_exp_shift_wx ( wE, wF, g : positive ) return positive;
  function log2 ( x : positive ) return integer;
  
  component fp_exp_shift is
    generic ( wE : positive;
              wF : positive;
              g : positive );
    port ( fpX : in  std_logic_vector(wE+wF downto 0);
           nX  : out std_logic_vector(wE+wF+g-1 downto 0);
           ofl : out std_logic;
           ufl : out std_logic );
  end component;
  
$
    port ( x : in  std_logic_vector(2+wE+wF downto 0);
           r : out std_logic_vector(2+wE+wF downto 0) );
  end component;
end package;

package body pkg_fp_exp is
  function min ( x, y : integer ) return integer is
  begin
    if x <= y then
      return x;
    else
      return y;
    end if;
  end function;

  function max ( x, y : integer ) return integer is
  begin
    if x >= y then
      return x;
    else
      return y;
    end if;
  end function;
  
  function fp_exp_shift_wx ( wE, wF, g : positive ) return positive is
  begin
    return min(wF+g, 2**(wE-1)-1);
  end function;
  
  function log2 ( x : positive ) return integer is
    variable n : natural := 0;
  begin
    while 2**(n+1) <= x loop
      n := n+1;
    end loop;
    return n;
  end function;

end package body;

-- Conversion de l'entrée en virgule fixe
-- ======================================

library ieee;
use ieee.std_logic_1164.all;
use ieee.std_logic_arith.all;
use ieee.std_logic_unsigned.all;
library work;
use work.pkg_fp_exp.all;

entity fp_exp_shift is
  generic ( wE : positive;
            wF : positive;
            g : positive );
  port ( fpX : in  std_logic_vector(wE+wF downto 0);
         nX  : out std_logic_vector(wE+wF+g-1 downto 0);
         ofl : out std_logic;
         ufl : out std_logic );
end entity;

architecture arch of fp_exp_shift is
  -- longueur de la partie fractionnaire de x
  constant wX : integer  := fp_exp_shift_wx(wE, wF, g);
  -- nombre d'étapes du décalage 
  -- (de l'ordre de log2(taille du nombre en virgule fixe))
  constant n  : positive := log2(wX+wE-2)+1;

  signal e0 : std_logic_vector(wE+1 downto 0);
  signal eX : std_logic_vector(wE+1 downto 0);

  signal mXu : std_logic_vector(wF downto 0);
  signal mXs : std_logic_vector(wF+1 downto 0);

  signal buf : std_logic_vector((n+1)*(wF+2**n+1)-1 downto 0);
begin
  -- évalue le décalage à effectuer
  e0 <= conv_std_logic_vector(2**(wE-1)-1 - wX, wE+2);
  eX <= ("00" & fpX(wE+wF-1 downto wF)) - e0;

  -- underflow quand l'entrée est arrondie à zéro (donc au final exp(entrée) = 1) (?)
  ufl <= eX(wE+1);
  -- overflow (détection partielle en se basant uniquement sur l'exposant de l'entrée)
  ofl <= not eX(wE+1) when eX(wE downto 0) > conv_std_logic_vector(wX+wE-2, wE+1) else
         '0';

  -- mantisse de l'entrée (rajoute le 1 implicite)
  mXu <= "1" & fpX(wF-1 downto 0);
  -- représentation signée de la mantisse
  mXs <= (wF+1 downto 0 => '0') - ("0" & mXu) when fpX(wE+wF) = '1' else ("0" & mXu);

  -- ajoute eX zéros à droite de la mantisse
  buf(wF+1 downto 0) <= mXs;
  shift : for i in 0 to n-1 generate
    buf( (i+1)*(wF+2**n+1) + wF+2**(i+1) downto
         (i+1)*(wF+2**n+1) )
      <=   -- pas de décalage si eX(i) = 0
           ( 2**i-1 downto 0 => buf(i*(wF+2**n+1) + wF+2**i) ) &
           buf( i*(wF+2**n+1) + wF+2**i downto
                i*(wF+2**n+1) )
        when eX(i) = '0' else
           -- décalage de 2 ^ i bits si eX(i) = 1
           buf( i*(wF+2**n+1) + wF+2**i downto
                i*(wF+2**n+1) ) &
           ( 2**i-1 downto 0 => '0' );
  end generate;

  no_padding : if wX >= g generate
    nX <= buf(n*(wF+2**n+1)+wF+wE+wX-1 downto n*(wF+2**n+1)+wX-g);
  end generate;

  padding : if wX < g generate
    nX <= buf(n*(wF+2**n+1)+wF+wE+wX-1 downto n*(wF+2**n+1)) & (g-wX-1 downto 0 => '0');
  end generate;

end architecture;

-- Exponentielle en virgule flottante
-- ==================================

library ieee;
use ieee.std_logic_1164.all;
use ieee.std_logic_arith.all;
use ieee.std_logic_unsigned.all;
library work;
use work.pkg_exp.all;
use work.pkg_fp_exp.all;

$

  signal nX : std_logic_vector(wE+wF+g-1 downto 0);
  signal nK0 : std_logic_vector(wE+4+wE downto 0);
  signal nK1 : std_logic_vector(wE+4+wE+1 downto 0);
  signal nK  : std_logic_vector(wE downto 0);
  
  signal nKLog20 : std_logic_vector(wE+wE-1+wF+g-1 downto 0);
  signal nKLog2  : std_logic_vector(wE+wE-1+wF+g downto 0);
  signal nY  : std_logic_vector(wE+wF+g-1 downto 0);
  signal sign : std_logic;
  signal unsigned_input : std_logic_vector(wF+g-2 downto 0);
  
  signal nZ : std_logic_vector(wF+g-1 downto 0);
  signal significand : std_logic_vector(wF+g-1 downto g);
  signal exponent : std_logic_vector(wE downto 0);

  signal sticky : std_logic;
  signal round  : std_logic;

  signal fR0 : std_logic_vector(wF+1 downto 0);
  signal fR1 : std_logic_vector(wF downto 0);
  signal fR  : std_logic_vector(wF-1 downto 0);

  signal eR : std_logic_vector(wE downto 0);
  
  signal ofl0 : std_logic;
  signal ofl1 : std_logic;
  signal ofl2 : std_logic;
  signal ufl0 : std_logic;
  signal ufl1 : std_logic;
  
begin
  shift : fp_exp_shift
    generic map ( wE => wE,
                  wF => wF,
                  g => g )
    port map ( fpX => X(wE+wF downto 0),
               nX  => nX,
               ofl => ofl0,
               ufl => ufl0 );

  nK0 <= nX(wE+wF+g-2 downto wF+g-4) * cstInvLog2;
  nK1 <= ("0" & nK0) - ("0" & cstInvLog2 & (wE+4-2 downto 0 => '0')) when nX(wE+wF+g-1) = '1' else
         "0" & nK0;

  nK <= nK1(wE+4+wE+1 downto 4+wE+1) + ((wE downto 1 => '0') & nK1(4+wE));

  nKLog20 <= nK(wE-1 downto 0) * cstLog2;
  nKLog2  <= ("0" & nKLog20) - ("0" & cstLog2 & (wE-1 downto 0 => '0')) when nK(wE) = '1' else
             "0" & nKLog20;

  nY <= nX - nKLog2(wE+wE-1+wF+g-1 downto wE-1);
  sign <= nY(wF+g-1);
  unsigned_input <= nY(wF+g-2 downto 0) when sign = '0' else (wF+g-2 downto 0 => '0') - nY(wF+g-2 downto 0);
  
$
    port map (x    => unsigned_input,
              y    => nZ,
              sign => sign);

  significand <= nZ(wF+g-1 downto g)   + ((wF-g-1 downto g+1 => '0') & nZ(g-1)) when sign = '0' else
                 nZ(wF+g-2 downto g-1) + ((wF-g-2 downto g   => '0') & nZ(g-2));
  exponent <= nK + ("00" & (wE-2 downto 1 => '1') & (not sign));

  ofl1 <= '1' when exponent(wE-1 downto 0) = (wE-1 downto 0 => '0') else
          '1' when exponent(wE-1 downto 0) = (wE-1 downto 0 => '1') else
          ofl0 or exponent(wE);

  ufl1 <= '1' when X(wE+wF+2 downto wE+wF+1) = "00" else
          ufl0;

  ofl2 <= '1' when X(wE+wF+2 downto wE+wF+1) = "10" else
          ofl1 and (not ufl1);
  
  R(wE+wF+2 downto wE+wF+1) <= "11"                   when X(wE+wF+2 downto wE+wF+1) = "11" else
                                 (not X(wE+wF)) & "0" when ofl2 = '1'                         else
                                 "01";

  R(wE+wF downto 0) <= "00" & (wE-2 downto 0 => '1') & (wF-1 downto 0 => '0') when ufl1 = '1' else
                         "0" & exponent(wE-1 downto 0) & significand;
end architecture;