Re: [myhdl-list] Slicing an unsigned intbv to a signed one

[Günter D. <dan...@we...>]

Christopher L. Felton wrote:
> Ok, below was my quick test to double check if it could be done.  A  
> real implementation probably need more thought (if feasible at all).
...

I think what you need to do is not just multiply by -1, but create a 
mask that is ORed with the actual number. If the sign bit gets set, the 
mask will be all 1 upwards from the sign bit and all 0 down to bit 0. 
Then OR that with the current intbv value.

So instead of this:

   self._val = -1 * self._val

do this:

   self._val = (-1 << self._nrbits-2) | self._val

This is basically a merging between the existing bits below the sign bit 
and the sign change to negative.

For clearing the sign bit the simplest way would be to slice the bits 
below the sign bit out and return them as a new intbv value.

Guenter