signal_processing/hardware/system/float.vhd

library ieee;
use ieee.std_logic_1164.all;
use ieee.numeric_std.all;

package float is
    constant SIGN : std_logic_vector( 31 downto 31 ) := ( others => '0' );
    constant EXP : std_logic_vector( 30 downto 23 ) := ( others => '0' );
    constant MANTISSA : std_logic_vector( 22 downto 0 ) := ( others => '0' );

    function find_leftmost( arg : unsigned; value : std_ulogic ) return integer;

    function count_leading_digits( arg : unsigned; value : std_ulogic ) return integer;

    function to_float( arg : std_logic_vector ) return std_logic_vector;

    function to_fixed( arg : std_logic_vector ) return std_logic_vector;

end package float;

package body float is
    function find_leftmost( arg : unsigned; value : std_ulogic ) return integer is
    begin
        for i in arg'left downto arg'right loop
            if ( arg( i ) = value ) then
                return i;
            end if;
        end loop;

        return -1;
    end function find_leftmost;

    function count_leading_digits( arg : unsigned; value : std_ulogic ) return integer is
        variable left_most_value : integer range -1 to arg'high;
        variable leading_values : integer range 0 to arg'high;
    begin
        left_most_value := find_leftmost( arg, not value );
        leading_values := 0;

        if ( left_most_value /= -1 ) then
            leading_values := arg'high - left_most_value;
        end if;

        return leading_values;
    end function count_leading_digits;

    function to_float( arg : std_logic_vector ) return std_logic_vector is
        variable y : std_logic_vector( 31 downto 0 );
        variable s : std_logic;
        variable e : unsigned( 7 downto 0 );
        variable m : unsigned( 22 downto 0 );
        variable value : unsigned( 30 downto 0 );

        variable leading_sign_digits : integer range 0 to value'high;
        variable reminding : integer range 0 to value'high;
    begin
        s := arg( 31 );

        if ( s = '0' ) then
            value := unsigned( arg( 30 downto 0 ) );
        else
            value := not unsigned( arg( 30 downto 0 ) );
            value := value +1;
        end if;
        leading_sign_digits := count_leading_digits( value, '0' );
        reminding := value'high - leading_sign_digits;
        e := to_unsigned( 126 - leading_sign_digits, e'length );

        if ( reminding > m'length ) then
            m := value( reminding - 1 downto reminding - m'length );
        elsif ( reminding > 1 ) then
            m := ( others => '0' );
            m( m'high downto m'high - reminding + 1 ) := value( reminding - 1 downto 0 );
        else
            m := ( others => '0' );
        end if;

        if (arg = x"00000000") then
            y := (others => '0');
        else
            y := s & std_logic_vector( e ) & std_logic_vector( m );
        end if;

        return y;
    end function to_float;

    function to_fixed( arg : std_logic_vector ) return std_logic_vector is
        variable y : unsigned( 31 downto 0 );
        variable s : std_logic;
        variable e : unsigned( 7 downto 0 );
        variable m_index_max : integer range -127 to 128;

    begin
        s := arg( 31 );
        e := unsigned(arg(30 downto 23));
        m_index_max := to_integer(signed(30-(126-e)));

        if (arg = x"00000000") then
            y := (others => '0');
        else
            y := (others => '0');
            case m_index_max is
                when 30 => y(30 downto 7):= '1' & unsigned( arg(22 downto 0) );
                when 29 => y(29 downto 6):= '1' & unsigned( arg(22 downto 0) );
                when 28 => y(28 downto 5):= '1' & unsigned( arg(22 downto 0) );
                when 27 => y(27 downto 4):= '1' & unsigned( arg(22 downto 0) );
                when 26 => y(26 downto 3):= '1' & unsigned( arg(22 downto 0) );
                when 25 => y(25 downto 2):= '1' & unsigned( arg(22 downto 0) );
                when 24 => y(24 downto 1):= '1' & unsigned( arg(22 downto 0) );
                when 23 => y(23 downto 0):= '1' & unsigned( arg(22 downto 0) );
                when 22 => y(22 downto 0):= '1' & unsigned( arg(22 downto 1) );
                when 21 => y(21 downto 0):= '1' & unsigned( arg(22 downto 2) );
                when 20 => y(20 downto 0):= '1' & unsigned( arg(22 downto 3) );
                when 19 => y(19 downto 0):= '1' & unsigned( arg(22 downto 4) );
                when 18 => y(18 downto 0):= '1' & unsigned( arg(22 downto 5) );
                when 17 => y(17 downto 0):= '1' & unsigned( arg(22 downto 6) );
                when 16 => y(16 downto 0):= '1' & unsigned( arg(22 downto 7) );
                when 15 => y(15 downto 0):= '1' & unsigned( arg(22 downto 8) );
                when 14 => y(14 downto 0):= '1' & unsigned( arg(22 downto 9) );
                when 13 => y(13 downto 0):= '1' & unsigned( arg(22 downto 10) );
                when 12 => y(12 downto 0):= '1' & unsigned( arg(22 downto 11) );
                when 11 => y(11 downto 0):= '1' & unsigned( arg(22 downto 12) );
                when 10 => y(10 downto 0):= '1' & unsigned( arg(22 downto 13) );
                when 9 => y(9 downto 0):= '1' & unsigned( arg(22 downto 14) );
                when 8 => y(8 downto 0):= '1' & unsigned( arg(22 downto 15) );
                when 7 => y(7 downto 0):= '1' & unsigned( arg(22 downto 16) );
                when 6 => y(6 downto 0):= '1' & unsigned( arg(22 downto 17) );
                when 5 => y(5 downto 0):= '1' & unsigned( arg(22 downto 18) );
                when 4 => y(4 downto 0):= '1' & unsigned( arg(22 downto 19) );
                when 3 => y(3 downto 0):= '1' & unsigned( arg(22 downto 20) );
                when 2 => y(2 downto 0):= '1' & unsigned( arg(22 downto 21) );
                when 1 => y(1 downto 0):= '1' & unsigned( arg(22 downto 22) );
                when 0 => y(0):= '1';
                when others => null;
            end case;
            if ( s = '1' ) then
                y := not(y);
                y:=  y + x"00000001";
            end if;
        end if;

        return std_logic_vector( y );
    end function to_fixed;

end package body float;