Re: [myhdl-list] Can't compare Signal(enum)

[Christopher F. <chr...@gm...>]

On 7/28/2014 7:08 AM, Thomas Heller wrote:
> I cannot compare signals containing enum instances; this looks like a
> bug to me:
>
> c:\Users\thomas\ip>py -2.7-32
> Python 2.7.7 (default, Jun  1 2014, 14:17:13) [MSC v.1500 32 bit
> (Intel)] on win32
> Type "help", "copyright", "credits" or "license" for more information.
>   >>> import myhdl
>   >>>
>   >>> state = myhdl.enum("foo", "bar")
>   >>>
>   >>> a = myhdl.Signal(state.foo)
>   >>> b = myhdl.Signal(state.bar)
>   >>>
>   >>> print a == b
> Traceback (most recent call last):
>     File "<stdin>", line 1, in <module>
>     File "C:\Python27\lib\site-packages\myhdl\_Signal.py", line 479, in
> __cmp__
>       return cmp(self._val, other)
>     File "C:\Python27\lib\site-packages\myhdl\_enum.py", line 109, in
> _notImplementedCompare
>       raise NotImplementedError
> NotImplementedError
>   >>>
>

Yes, I would agree this is unexpected behavior.

The problem is the use of the "cmp" function in
the Signal class.  The cmp(x, y) [1] function performs
a x > y which is not implemented in the enum class
(good reason).  The use-case of a Signal(enum) ==
Signal(enum) probably has not been used, but I agree
it is a valid case.

     import myhdl

     state = myhdl.enum("foo", "bar")

     a = myhdl.Signal(state.foo)
     b = myhdl.Signal(state.bar)

     print a == state.foo
     print a == state.bar
     print b == state.foo
     print b == state.bar
     print a == b

Only the Signal(enum) == Signal(enum) fails because the
Signal comparison calls.  This should be added as an issue
in the repo tracker [2].

Regards,
Chris

[1] https://docs.python.org/2/library/functions.html?highlight=cmp#cmp
[2] https://bitbucket.org/jandecaluwe/myhdl/issues?status=new&status=open