need the unsigned value from dl.call()

[eliss]

On Dec 11, 12:38 pm, Larry Bates <larry.ba... at websafe.com> wrote:
> Diez B. Roggisch wrote:
> > Larry Bates wrote:
>
> >> eliss wrote:
> >>> I'm using dl.call() to call a C function in an external library. It's
> >>> working great so far except for one function, which returns an
> >>> unsigned int in the C version. However, in python it returns a signed
> >>> value to me. How can I get the unsigned value from this? I haven't
> >>> brushed up on my two's complement in a while, so I was hoping someone
> >>> could give me a hand.
>
> >>> Thanks
>
> >>> eliss
> >> It is returning 32 bits.  If the sign bit (bit 32) is on it appears as a
> >> negative number.  Test for negative and multiply the absolute value * 2.
> >> That should get you the unsigned value you want in a long.
>
> > Erm... Nope.
>
> > All bits set is -1 - so according to your recipe, that would be abs(-1) * 2
> > = 2
>
> > I'd suggest this formula:
>
> > if value < 0:
> >     value = 2^32 + value + 1
>
> > Diez
>
> Thanks for the correction.  You are of course correct.
>
> -Larry

Hi thanks for the responses but I'm afraid I don't see how either
formula works.

Lets say I get the return value of -5, which is 1011b when it should
be 11. Then according to the formula it would be 2^4-5+1=12

But it should be 11...