---------------------------------------------------------------------- Company       : XESS Corp.-- Engineer      : Dave Vanden Bout-- Creation Date : 05/17/2005-- Copyright     : 2005, XESS Corp-- Tool Versions : WebPACK 6.3.03i---- Description:--    Miscellaneous VHDL constants and functions.---- Revision:--    1.3.0---- Additional Comments:--    1.3.0:--        Added int_max() function.--    1.2.0:--        Added binary2gray() and gray2binary() functions.--    1.1.0:--        Added int_select() and real_select() functions.--    1.0.0:--        Initial release.---- License:--    This code can be freely distributed and modified as long as--    this header is not removed.--------------------------------------------------------------------library IEEE;use IEEE.std_logic_1164.all;use IEEE.numeric_std.all;package common is  constant YES       :    std_logic := '1';  constant NO        :    std_logic := '0';  constant HI        :    std_logic := '1';  constant LO        :    std_logic := '0';  constant ONE       :    std_logic := '1';  constant ZERO      :    std_logic := '0';  constant HIZ       :    std_logic := 'Z';    -- Types of FPGA chips.  constant SPARTAN2  : natural := 1;  constant SPARTAN2E : natural := 2;  constant SPARTAN3  : natural := 3;  -- Convert a Boolean to a std_logic.  function boolean2stdlogic(b : in boolean) return std_logic;  -- Find the base-2 logarithm of a number.  function log2(v : in natural) return natural;  -- Select one of two integers based on a Boolean.  function int_select(s : in boolean; a : in integer; b : in integer) return integer;  -- Select one of two reals based on a Boolean.  function real_select(s : in boolean; a : in real; b : in real) return real;  -- Convert a binary number to a graycode number.  function binary2gray(b: in std_logic_vector) return std_logic_vector;  -- Convert a graycode number to a binary number.  function gray2binary(g: in std_logic_vector) return std_logic_vector;  -- Find the maximum of two integers.  function int_max(a: in integer; b: in integer) return integer;end package common;library IEEE;use IEEE.std_logic_1164.all;use IEEE.numeric_std.all;package body common is  -- Convert a Boolean to a std_logic.  function boolean2stdlogic(b : in boolean) return std_logic is    variable s                :    std_logic;  begin    if b then      s := '1';    else      s := '0';    end if;    return s;  end function boolean2stdlogic;  -- Find the base 2 logarithm of a number.  function log2(v : in natural) return natural is    variable n    :    natural;    variable logn :    natural;  begin    n      := 1;    for i in 0 to 128 loop      logn := i;      exit when (n >= v);      n    := n * 2;    end loop;    return logn;  end function log2;  -- Select one of two integers based on a Boolean.  function int_select(s : in boolean; a : in integer; b : in integer) return integer is  begin    if s then      return a;    else      return b;    end if;    return a;  end function int_select;  -- Select one of two reals based on a Boolean.  function real_select(s : in boolean; a : in real; b : in real) return real is  begin    if s then      return a;    else      return b;    end if;    return a;  end function real_select;  -- Convert a binary number to a graycode number.  function binary2gray(b: in std_logic_vector) return std_logic_vector is    variable g: std_logic_vector(b'range);  begin    for i in b'low to b'high-1 loop      g(i) := b(i) XOR b(i+1);    end loop;    g(b'high) := b(b'high);    return g;  end function binary2gray;  -- Convert a graycode number to a binary number.  function gray2binary(g: in std_logic_vector) return std_logic_vector is    variable b: std_logic_vector(g'range);  begin    b(b'high) := g(b'high);    for i in g'high-1 downto g'low loop      b(i) := b(i+1) XOR b(i);    end loop;    return b;  end function gray2binary;  -- Find the maximum of two integers.  function int_max(a: in integer; b: in integer) return integer is  begin    if a>b then      return a;    else      return b;    end if;    return a;  end function int_max;end package body common;