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What return value should be besides '0' and '1' for this function?

Hi,

I read the following code. I know that std_logic has value '0', '1', 'Z' and
'X' etc.

There are only two values are considered below. Do you think it is an 
 imperfect function or not?


Thanks,




  FUNCTION to_integer( x : IN std_logic) RETURN integer IS
    VARIABLE int: integer;
  BEGIN
    IF x = '0' THEN
      int := 0;
    ELSE
      int := 1;
    END IF;
    RETURN int;
  END;
0
fl
5/23/2015 2:31:09 AM
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On 5/22/2015 10:31 PM, fl wrote:
> Hi,
>
> I read the following code. I know that std_logic has value '0', '1', 'Z' and
> 'X' etc.
>
> There are only two values are considered below. Do you think it is an
>   imperfect function or not?
>
>
> Thanks,
>
>
>
>
>    FUNCTION to_integer( x : IN std_logic) RETURN integer IS
>      VARIABLE int: integer;
>    BEGIN
>      IF x = '0' THEN
>        int := 0;
>      ELSE
>        int := 1;
>      END IF;
>      RETURN int;
>    END;

Not sure why you say only two values are "considered".  The input can be 
any of a number of states and all are translated to an integer 1 except 
for the input of '0' which is translated to 0.  Is that what you want? 
std_logic can also be 'H' or 'L' which are often equated to '1' and '0' 
respectively.

-- 

Rick
0
rickman
5/23/2015 2:40:06 AM
On Fri, 22 May 2015 19:31:09 -0700, fl wrote:

> Hi,

> There are only two values are considered below. Do you think it is an
>  imperfect function or not?
> 

As Rickman hints, this function is definitely erroneous in converting 'L' 
to '1'.

If you are only allowed 0 and 1 as return values, there is no choice but 
to resolve all the others 'U','Z' etc to either 0 or 1, and your choice 
to resolve them (except for 'L') as 1 is probably as good as any.

I would recommend declaring a new Integer type (or at the very  least a 
subtype) restricted in range to (0 to 1) and return that type, to make it 
crystal clear what this function does (and to catch unintended errors 
such as passing 2 (or -2143863148) as a value to code which was only 
written to handle 0,1.

-- Brian
0
Brian
5/23/2015 9:52:30 AM
On Saturday, May 23, 2015 at 2:53:43 AM UTC-7, Brian Drummond wrote:
> On Fri, 22 May 2015 19:31:09 -0700, fl wrote:
> 
> > Hi,
> 
> > There are only two values are considered below. Do you think it is an
> >  imperfect function or not?
> > 
> 
> As Rickman hints, this function is definitely erroneous in converting 'L' 
> to '1'.
> 
> If you are only allowed 0 and 1 as return values, there is no choice but 
> to resolve all the others 'U','Z' etc to either 0 or 1, and your choice 
> to resolve them (except for 'L') as 1 is probably as good as any.
> 
> I would recommend declaring a new Integer type (or at the very  least a 
> subtype) restricted in range to (0 to 1) and return that type, to make it 
> crystal clear what this function does (and to catch unintended errors 
> such as passing 2 (or -2143863148) as a value to code which was only 
> written to handle 0,1.
> 
> -- Brian

Great thanks to both of you.
0
fl
5/24/2015 1:47:32 AM
Reply:

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