fadd.vhd

32位元浮点数加法器,用于以VHDL编写的32位元CPU

package commonConstants is
	constant wordSize: integer := 32;
	constant adrLength: integer := 16;
end package commonConstants;

library ieee;
use IEEE.STD_LOGIC_1164.ALL;
use IEEE.STD_LOGIC_ARITH.ALL;
use IEEE.STD_LOGIC_UNSIGNED.ALL;
use work.commonConstants.all;

-- FP Adder (32-bit: 1 bit sign, 8 bits exponent, 23 bits mantissa)
-- positive = 0, negtive = 1

package pack_CC_fun is    
    function fadd (x : std_logic_vector(wordSize-1 downto 0);
                   y : std_logic_vector(wordSize-1 downto 0)
                   -- z : std_logic_vector (31 downto 0);
                   -- testflag :out std_logic;
		             -- ov: out std_logic
		   ) return STD_LOGIC_VECTOR;       
end pack_CC_fun;

package BODY pack_CC_fun is
    function fadd (x : std_logic_vector(wordSize-1 downto 0);
                   y : std_logic_vector(wordSize-1 downto 0)
                   -- z : std_logic_vector (31 downto 0);
                   -- testflag :out std_logic;
		             -- ov: out std_logic
		   ) return STD_LOGIC_VECTOR is
variable z : std_logic_vector (wordSize-1 downto 0);

-- process(x,y) 
-- variable declaration
variable m1,m2:std_logic_vector (47 downto 0);  
-- temporary  storage of                                                                                                                                                 
-- mantissa including implicit '1' 
variable tempm:std_logic_vector (47 downto 0);       
-- temporary storage of mantissa             
variable tempm2:std_logic_vector (93 downto 0);
-- -- temporary storage of final mantissa
variable m:std_logic_vector(22 downto 0);            
-- final mantissa result
variable e:std_logic_vector (7 downto 0);           
-- resultant exponent
variable e1,e2:std_logic_vector(8 downto 0);        
-- temporary storage of exponents
variable tempe:std_logic_vector(8 downto 0);        
-- temporary resultant exponent
variable s,xs,ys : std_logic;	                      
-- final sign bit,s and signs as and bs of a and b
variable bias:std_logic_vector(8 downto 0);         
-- exponent bias
variable i:integer;
variable j:integer;

            
begin
    m1 := "0000000000000000000000001" & x(22 downto 0); 	 
    -- m1, mantissa of 'x' including implicit '1'
    m2 := "0000000000000000000000001" & y(22 downto 0); 	 
    -- m2, mantissa of 'y' including implicit '1'
    e1 := '0' & x(30 downto 23);  
    -- exponent of x to e1 (add in leading zero to
    -- e1 and e2 for extra precision and for 
    -- overflow detection)
    e2 := '0' & y(30 downto 23);  
    -- exponent of y to e2
    xs := x(31);		        	         
    -- sign of x 
    ys := y(31);		        	         
    -- sign of y
    --ov <= '0';                    
    -- set overflow flag to cleared (no overflow, no error)
    tempm:="000000000000000000000000000000000000000000000000"; 
    tempm2:="0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"; 
    -- clear mantissa for calculation
    tempe:="000000000";
    -- clear exponent for calculation
    
    --**********     add the mantissas     **********--
    if e1(8 downto 0) = "000000000"  then
      if m1(22 downto 0) = "00000000000000000000000" then
        s := ys;
        e := e2(7 downto 0);
        m := m2(22 downto 0);
      else
        s := '0';
        e := "00000000";
        m := "00000000000000000000000";
      end if;
    elsif e1(8 downto 0) = "011111111"   then
      s := '0';
      e := "11111111";
      m := "00000000000000000000000";  
      --ov <= '1';     
        -- x error (NAN or infinity)
    else
      if e2(8 downto 0) = "000000000"   then
        if m2(22 downto 0) = "00000000000000000000000" then
          s := xs;
          e := e1(7 downto 0);
          m := m1(22 downto 0);
        else
          s := '0';
          e := "00000000";
          m := "00000000000000000000000";
        end if;
      elsif e2(8 downto 0) = "011111111"   then
        s := '0';
        e := "11111111";
        m := "00000000000000000000000";  
        --ov <= '1';     
        -- y error   
      else
        if (e1 = e2 and m1 = m2 )   then
          if xs /= ys   then
            s := '0';
            e := "00000000";
            m := "00000000000000000000000";
            --ov <= '0';         
          else
            tempm := m1 + m2;
            s := xs XOR ys;
            m := tempm(23 downto 1);
            e := e1(7 downto 0);
            e := e + "00000001";
            --ov <= '0';
          end if;
        else
          if xs = ys   then
            if e1 = e2   then      
              tempm := m1 + m2;
              s := xs XOR ys;
              m := tempm(23 downto 1);
              e := e1(7 downto 0);
              e := e + "00000001";
              --ov <= '0';
            elsif e1 > e2   then
              s := xs XOR ys;
              bias := e1 - e2;
                if bias > "00010111"   then
                  e := e1(7 downto 0);
                  m := m1(22 downto 0);
                  --ov <= '0';
                  -- y almost zero  
                else
                  i := 0;
                  loop
                    e2 := e2 + "000000001";
                  ---------------------------------------
                    j := 0;
                    loop
                      m1(46 - j) := m1(45 - j);
                      j := j + 1;
                    exit when j = 46;
                    end loop;
                    m1(0) := '0';
                  ----------Shift Mantissa---------------          
                    i := i + 1;
                  exit when e1 = e2;
                  end loop;
                    tempm := m1 + m2;
                    if tempm( 24 + i ) = '1'   then
                      e2 := e2 + "000000001";
                      m := tempm( 23 + i downto i + 1 );
                      e := e2(7 downto 0);
                      --ov <= '0';
                    else
                      m := tempm( 22 + i downto i );
                      e := e2(7 downto 0);
                      --ov <= '0';    
                    end if;  
                end if;
            else
              s := xs XOR ys;
              bias := e2 - e1;
              if bias > "00010111"   then
                e := e2(7 downto 0);
                m := m2(22 downto 0);
                --ov <= '0';
                -- x almost zero
              else
                i := 0;
                loop
                  e1 := e1 + "000000001";
                ---------------------------------------
                  j := 0;
                  loop
                    m2(46 - j) := m2(45 - j);
                    j := j + 1;
                  exit when j = 46;
                  end loop;
                  m2(0) := '0';
                ----------Shift Mantissa---------------
                  i := i + 1;
                exit when e1 = e2;
                end loop;
                  tempm := m1 + m2;
                  if tempm( 24 + i ) = '1'   then
                    e1 := e1 + "000000001";
                    m := tempm( 23 + i downto i + 1 );
                    e := e1(7 downto 0);
                    --ov <= '0';
                  else
                    m := tempm( 22 + i downto i );
                    e := e1(7 downto 0);
                    --ov <= '0';    
                  end if;  
              end if;    
            end if;
          else
          -- xs /= ys
            if e1 > e2  then
              s := xs;
              bias := e1 - e2;
              if bias > "000010111"   then
                e := e1(7 downto 0);
                m := m1(22 downto 0);
                --ov <= '0';  
                -- y almost zero
              else
                i := 0;
                loop
                  e2 := e2 + "000000001";
                  j := 0;
                  loop
                    m1(46 - j) := m1(45 - j);
                    j := j + 1;
                  exit when j = 46;
                  end loop;
                  m1(0) := '0';  
                  i := i + 1;
                exit when e1 = e2;
                end loop;
                ----------Shift Mantissa---------------
                  tempm := m1 - m2;
                  tempm2( 70 downto 23 ) := tempm( 47 downto 0 );
                    j := 0;
                    e1 :=  e1 + "000000001";
                    loop
                      m := tempm2( 45 + i - j downto 23 + i - j );
                      j := j + 1;
                      e1 :=  e1 - "000000001"; 
                    exit when tempm2( 47 + i - j ) = '1';
                    end loop;
                    e := e1(7 downto 0);
                ----------Shift Mantissa---------------
              end if;    
            elsif e1 < e2  then
              s := ys;
              bias := e2 - e1;
              if bias > "000010111"   then
                e := e1(7 downto 0);
                m := m2(22 downto 0);
                --ov <= '0';  
                -- x almost zero
              else
                i := 0;
                loop
                  e1 := e1 + "000000001";
                  j := 0;
                  loop
                    m2(46 - j) := m2(45 - j);
                    j := j + 1;
                  exit when j = 46;
                  end loop;
                  m2(0) := '0';  
                  i := i + 1;
                exit when e1 = e2;
                end loop;
                ----------Shift Mantissa---------------                         
                  tempm := m2 - m1;
                  tempm2( 70 downto 23 ) := tempm( 47 downto 0 );
                    j := 0;
                    e2 :=  e2 + "000000001";
                    loop
                      m := tempm2( 45 + i - j downto 23 + i - j );
                      j := j + 1;
                      e2 :=  e2 - "000000001"; 
                    exit when tempm2( 47 + i - j ) = '1';
                    end loop;
                    e := e2(7 downto 0);
                ----------Shift Mantissa--------------- 
              end if;
            else
            -- e1 = e2
            -- m1 /= m2
            ----------------------------------------------------
              if m1 > m2   then
                s := xs;
                tempm := m1 - m2;
                e := e1( 7 downto 0 );
                m := tempm(22 downto 0);
            -----------------------------------------------------------------  
              elsif m1 < m2   then
                s := ys;         
                tempm := m2 - m1;
                e := e2( 7 downto 0 );
                m := tempm(22 downto 0);
              else 
                s := '0';
                tempm := "000000000000000000000000000000000000000000000000";
                e := "00000000";
                m := tempm(22 downto 0);
              end if;
            end if;   
          end if;
        end if;  
      end if;
    end if;        
z := s & e & m;
return z;
--end process; 
end fadd;
end pack_CC_fun;