Re: EXTERNAL: [vhdl-200x] VHDL ternary operation

On Thu, Mar 28, 2013 at 7:40 AM, Jones, Andy D <andy.d.jones@lmco.com> wrote:
> Daniel,
>
>
>
> "pass" when fault else "fail" is NOT an expression. It is the RHS of a
> conditional assignment statement. Such a RHS may contain expressions, but
> expressions may not contain a conditional assignment RHS.
>
>
>
> Since conditional assignments can be open-ended, in effect meaning that the
> assignment does not occur if no “when” expression evaluates as true, its use
> as an expression is not possible.
>
>
>
> To solve your immediate problem, you could write a function that takes a
> boolean argument and returns “pass” or “fail” strings, or you could create a
> constant array of two strings, indexed by boolean, e.g. (true => “fail”,
> false => “pass”). Then you could include the function call or constant in
> your report expression.

It's a hard problem. 'Just write function' is good advice. -- MT

------------------------------------------------------------------------------
   function sel (                                  -- sel(false,a,b) => a
      choice : boolean;                         -- sel( true,a,b) => b
      t, f   : std_logic_vector)                -- works like  "arg ? a:b"
      return std_logic_vector
   is
   begin
      if choice then return t; else return f; end if;
   end function sel;

------------------------------------------------------------------------------
   function push (                        -- Push byte into word, uses sel()
      byte       : in std_logic_vector;
      word       : in std_logic_vector;
      shift_left : in boolean := true)  -- left is default
      return std_logic_vector
   is  -- push byte into word from left or right
      variable byte_v :  std_logic_vector(byte'length-1 downto 0) := byte;
      variable word_v : std_logic_vector(word'length-1 downto 0) := word;
   begin
      return(
         sel(                    -- select value for true or false
            choice => shift_left,
            t =>              word_v(word_v'left - byte'length downto
0) & byte_v,
            f => byte_v & word_v(word_v'left     downto byte'length))
         );
   end function push;
>
>
> Andy
>
>
>
> From: owner-vhdl-200x@eda.org [mailto:owner-vhdl-200x@eda.org] On Behalf Of
> Daniel Kho
> Sent: Thursday, March 28, 2013 4:19 AM
> To: vhdl-200x@eda.org
> Subject: EXTERNAL: [vhdl-200x] VHDL ternary operation
>
>
>
> Hi all,
>
> I'm wondering if the current revision supports something like the following?
>
> report to_hstring(index) & ", " & ("pass" when fault else "fail") & lf &
> nul;
>
> where "index" is an unsigned vector, and "fault" is a boolean.
>
>
>
> The expression ("pass" when fault else "fail") can already be used directly
> in clocked processes, but I'm not too sure if the standard allows this to be
> used within report statements.
>
> If there's a better way of writing which could produce the same effect, do
> share with me as well.
>
>
>
> regards, daniel
>
>
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