Re: [myhdl-list] fixed-point thoughts : part two

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

<snip>
>>> The same turned, what about:
>>>    >>> fixedbv(1.25,min=-8,max=8,res=1/16.) + 1
>>> To be consistent with the suggestion, this would result in 1.3125. Not
>>> something I would expect.
>>
>> Currently, it would throw an error.
>
> Ah. It seems to me like this could be interesting when adding a
> constant; but it needs careful thought on what the effect on the min/max
> values of a returned fixedbv is (assuming a fixedbv is returned).
> Throwing an error would not block adding such a feature later on.
>

In my head, a constant has an implied format, and the
resolution is /res = 1/, the constant format would be
(assuming only integer constants for now):

     cc = fixbv(1, min=1, max=1+1, res=1)

When doing the operation above

     siii.iiii
   +        si
   -----------

The constant and the /fixbv/ are not aligned, so it needs
to throw an error.  To add a constant to an existing /fixbv/
the /resize/ function would need to be used or added to
a /fixbv/ with a /res = 1/

     >>> x = fixbv(1.25, min=-8, max=8, res=1/16)
     >>> x = x + resize(1,x)  # <-- resize to "x" format

For a complicated expression this gets a little unwieldy.

> Thanks for looking into this,
> Benjamin

Thanks for keeping me honest :)