CODEWITHSUNDEEP
vhdloverloadingpackquestasim
Katrine Grytten
Katrine Grytten

Reputation: 21

Overloading function in subprogram, but I it has "already been defined"

I'm trying to compile my subprogram pack and I get this error:

** Error: C:/Users/kmgrytte/Downloads/subprog_pck.vhd(16): (vcom-1295) Function "parity" has already been defined in this region. ** =====> Prior declaration of "parity" is at C:/Users/kmgrytte/Downloads/subprog_pck.vhd(12). ** Error: C:/Users/kmgrytte/Downloads/subprog_pck.vhd(20): VHDL Compiler exiting

Oveloading like this worked in my main program and I can't find any good examples of overloading in subprograms online. 

use IEEE.std_logic_1164.all;
use ieee.numeric_std.all;

package subprog_pck is
    procedure parity;
    procedure parity(
    in1 : in std_logic_vector(15 downto 0);
    in2 : in std_logic_vector(15 downto 0);
    par : out std_logic);

    function parity return std_logic;
    function parity(
    indata : in std_logic_vector(15 downto 0)) return std_logic;

    impure function parity return std_logic;
    impure function parity(
    indata : in unsigned(15 downto 0)) return std_logic;

end package subprog_pck;

package body subprog_pck is

procedure parity(
    in1 : in std_logic_vector(15 downto 0);
    in2 : in std_logic_vector(15 downto 0);
    par : out std_logic) is
    begin
    variable parity1, parity2 : std_logic:=0;
    if (rst_n = '0') then       
      parity1 := '0';
      parity2 := '0';
      par <= '0';
    elsif rising_edge(mclk) then
      parity1 := '0';
      for i in in1'range loop
        if in1(i) = '1' then
          parity1 := not parity1;
        end if;        
      end loop;      
      parity2 := '0';
      for j in in2'range loop
        parity2 := parity2 xor in2(j); 
      end loop;
      par <= parity1 xor parity2;
    end if;
    end parity;

function parity(indata : in std_logic_vector(15 downto 0))  return std_logic     is
    variable parity_var : std_logic := '0';
    begin
        for i in indata'range loop
            if (indata(i) = '1') then
                parity_var := not parity_var;
            end if;
        end loop;
    return parity_var;
end function parity;

function parity(indata : in unsigned(15 downto 0))
    return std_logic is
    variable parity_var : std_logic := '0';
    begin
        for j in indata'range loop  
            parity_var := parity_var xor indata(j);
        end loop;
    return parity_var;
end function parity;


end package body subprog_pck;

Upvotes: 2

Views: 1794

Answers (2)

user1155120
user1155120

Reputation:

There are additional errors in your package which is missing a library clause (library ieee;) in the context clause. The procedure parity has a variable declaration after begin, your initial values for parity1 and parity2 are 0 (a numeric literal), there's no declaration for rst_n or mclk, par in par <= ... is not a signal, there's no body for procedure parity or function parity with no parameters.

IEEE Std 1076-2008
12.3 Visibility

Two declarations that occur immediately within the same declarative region, other than the declarative region of a block implied by a component instantiation or the declarative region of a generic-mapped package or subprogram equivalent to a package instance or a subprogram instance, shall not be homographs, unless exactly one of them is the implicit declaration of a predefined operation or is an implicit alias of such an implicit declaration.

(There's no implicit declaration here and no predefined operation, emphasis added.)

Also in 12.3

... Each of two declarations is said to be a homograph of the other if and only if both declarations have the same designator, and they denote different named entities, and either overloading is allowed for at most one of the two, or overloading is allowed for both declarations and they have the same parameter and result type profile (see 4.5.1).

4.5 Subprogram overloading
4.5.1

Two formal parameter lists are said to have the same parameter type profile if and only if they have the same number of parameters, and if at each parameter position the corresponding parameters have the same base type. Two subprograms are said to have the same parameter and result type profile if and only if both have the same parameter type profile, and if either both are functions with the same result base type or neither of the two is a function.

You have more than one of these errors. vcom quit after the first one. The order in which errors are found are left to vagaries of the VHDL tool implementation applying semantic rules (other tools might find other errors first, explaining how the errors in the first paragraph above were found).

Modelsim has a verror tool providing more explanation:

vcom Message # 1295:
Two declarations that occur immediately within the same declarative region must not be homographs, unless exactly one of them is the declaration of a predefined operation. Each of two declarations is said to be a homograph of the other if both declarations have the same identifier, operator symbol, or character literal, and if overloading is allowed for at most one of the two. If overloading is allowed for both declarations, then each of the two is a homograph of the other if they have the same identifier, operator symbol, or character literal, as well as the same parameter and result type profile (see 3.1.1). Overloading is defined only for subprograms (including those those whose designator is an operator symbol) and enumeration literals (including character literals).
[DOC: IEEE Std 1076-1993 VHDL LRM - 10.3 Visibility]

(These references are from the -1993 revision of the standard.)

Upvotes: 0

Tricky
Tricky

Reputation: 4481

Function overloading only occurs when you have the same function name with a different parameter list. Using impure does not overload another function. So you have two version of parity that takes no inputs and outputs a std_logic. Hence the compile error.

You also didn't provide a this version of parity in the package body.

Upvotes: 1

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