Re: [myhdl-list] Error in Intbv class?

[Forumulator B. <for...@gm...>]

True, because the value wrapped by the class is still a standard
unconstrained int. Thus, accessing something like:

>>a=intbv(5)[4:]
>>a[6]
false

Where as it should raise an out of bounds exception.Can someone comment on
this so that I could possibly try to fix this.

While we're on the topic, i also think that the __setitem__ method should
be seperately implemented for modbv too, so that wrap around behaviour can
be extended to slices of an object. For example.

>>a=modbv(5)[4:]
>>a[4:1]=20

should give a value of 12 for a instead of giving an error. Are these
issues trivial?

On Thu, Mar 3, 2016 at 8:35 PM, Samuele Disegna <sm...@gm...> wrote:

> Hi again, while analyzing the _intbv code I noticed a related problem:
>
> An Exception is Not risen when accessing a out of bound bit of a
> constrained intbv.
> This seems a real problem to me.
>
> I tested it by using the example code at
> http://docs.myhdl.org/en/stable/manual/hwtypes.html#bit-indexing and
> modifing it for using a constrained intbv:
>
> from myhdl import Signal, delay, Simulation, always_comb, instance, intbv,
> bin
>
> def bin2gray(B, G, width):
>     """ Gray encoder.
>
>     B -- input intbv signal, binary encoded
>     G -- output intbv signal, gray encoded
>     width -- bit width
>     """
>
>     @always_comb
>     def logic():
>         for i in range(width):
>             G.next[i] = B[i+1] ^ B[i]
>
>     return logic
>
> def testBench(width):
>
>     B = Signal(intbv(0)[3:])
>     G = Signal(intbv(0)[3:])
>
>     dut = bin2gray(B, G, width)
>
>     @instance
>     def stimulus():
>         for i in range(2**width):
>             B.next = intbv(i)[3:]
>             yield delay(10)
>             print("B: " + bin(B, width) + "| G: " + bin(G, width))
>
>     return dut, stimulus
>
> sim = Simulation(testBench(width=3))
> sim.run()
>
>
> On Thu, Mar 3, 2016 at 2:24 PM, Samuele Disegna <sm...@gm...> wrote:
>
>> Hello, Last message was empty, my mistake.
>>
>> On Thu, Mar 3, 2016 at 2:10 PM, Samuele Disegna <sm...@gm...> wrote:
>>
>>>
>>>
>>> On Thu, Mar 3, 2016 at 1:14 PM, Forumulator Bing <for...@gm...>
>>> wrote:
>>>
>>>> Hello,
>>>>
>>>> I may have found a potential bug in intbv:
>>>>
>>>> >>> a=intbv(5)[4:0]
>>>> >>> a[6:0]=20
>>>> Traceback (most recent call last):
>>>>   File "<stdin>", line 1, in <module>
>>>>   File "/usr/local/lib/python3.4/dist-packages/myhdl/_intbv.py", line
>>>> 180, in __setitem__
>>>>     self._handleBounds()
>>>>   File "/usr/local/lib/python3.4/dist-packages/myhdl/_intbv.py", line
>>>> 77, in _handleBounds
>>>>     (self._val, self._max))
>>>> ValueError: intbv value 20 >= maximum 16
>>>> >>> a
>>>> intbv(20)
>>>>
>>>> It gives a ValueError, but still sets the value of a to 20. Would this
>>>> be considered a bug since an exception is thrown?
>>>>
>>>>
>>> From what I see on myhdl code min/max bounds handling is done later than
>> assignment and it seems independent.
>> Therefore I would say it is not a bug. We could document this behaviour.
>> Is it possible to subclass the exception to a documented ValueBoundError
>> that define the behaviour?
>>
>> You can find the related code at
>> https://github.com/jandecaluwe/myhdl/blob/master/myhdl/_intbv.py
>> def __setitem__(self, key, val):
>>
>> Regards
>>
>
>
>
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