Re: [Sbcl-help] [SPAM] Re: How to pass bignums to foreign routines?

[Christophe R. <cs...@ca...>]

Paul Khuong <pv...@pv...> writes:

> In article <871...@ca...>,
>  Christophe Rhodes <cs...@ca...> wrote:
>> I'm not sure why you think this is curious.  It sounds like Waldek is
>> saying that the in-memory representation of an sbcl bignum is
>> sufficiently close to an in-memory representation of a gmp bignum that
>> it's possible to pun them.  The disadvantage of doing a principled
>> translation between GMP structures and Lisp bignums is...
>
> It's not, unless you restrict yourself to positive integers. GMP integer 
> use a sign-magnitude representation, while we use 2's complement, 
> probably to simplify bit operations.

Well, that's a shame :-)  Oh well.

Then sb-alien can be used to write support routines for automatic
conversion to and from the GMP representation: defining alien type class
methods for naturalize-gen and deport-gen (look at the c-string methods
for inspiration).  This would allow Waldek to have an integrated feel
for whatever GMP calls he needs to make, I think.

Best,

Christophe