need the unsigned value from dl.call()

[eliss]

On Dec 11, 2:28 pm, eliss <eliss.carm... at gmail.com> wrote:
> 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...

Seems like the simple formula of:

if value < 0:
    value = 2^32 + value

might just work. Thanks :)