Re: [myhdl-list] Bit-wise inversion issue

[Christopher L. F. <cf...@uc...>]

Here is a possible enhancement,

from _intbv.py around line 407

<<code>>
     def __invert__(self):
         if self._nrbits:
             if self._min < 0:
                 return intbv(~self._val, min=self._min, max=self._max)
             else:
                 return intbv(~self._val & (1L << self._nrbits)-1)
         else:
             return intbv(~self._val)
<<>>

I ran the test scripts, it didn't break anything.  Also the sequential  
mult that I sent works with the 2's comp flip.


On Feb 28, 2008, at 7:00 AM, Christopher L. Felton wrote:

> Is the following expected behavior?
>
> >>> y = intbv(15)[4:]
> >>> ~y
> intbv(0L)
> >>> z = ~y
> >>> z._nrbits
> 0
> >>>
>
> The new number of bits is 0?  I think in normal case this is fine  
> because usually it would be Signal.next, and the Signal type  
> wouldn't be overridden only the value?
>
>
> On Feb 27, 2008, at 2:41 PM, Tom Dillon wrote:
>
>> Jan,
>>
>> On Wednesday 27 February 2008 02:33:57 pm Jan Decaluwe wrote:
>>
>>>>
>>>> intbv(5)[3:] is unsigned, so I think 2L is the right answer.
>>>
>>> That's not how I think about it. (Warning: this may get subtle.)
>>> To me, intbv(5)[3:] is simply intbv(5) with constraints on the  
>>> allowed
>>> values. If the constraints are such that the value must be positive,
>>> then we can choose to represent such an intbv as an unsigned in
>>> another language such as Verilog or VHDL. An optimization really.
>>
>> yes, I agree with you thinking there. I was thinking the slice  
>> would produce an unsigned intbv, but
>> of course that is wrong.
>>
>> I think it has to make sense and be as simple as possible in MyHDL  
>> and force the translation to
>> Verilog or VHDL to produce the same results.
>>
>>>
>>> On the other hand, I see your point of course. We should be
>>> practical. I have to think further, there may be compromise  
>>> solutions.
>>>
>>> In any case, there really is something wrong. Consider:
>>>>>> ~intbv(5, min=-6, max=6)
>>>
>>> intbv(10L)
>>
>> What about ~intbv(5,min=0, max=15)?
>>
>> intbv(10L)
>>
>> I think that is correct.
>>
>> Tom
>>
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