64 bit types and C libraries

[Daniel Keep]

Regan Heath wrote:
> Hi all,
> 
> I am throwing my hand at writing D ports of the OpenSSL libraries.  It looks like a mammoth task but I figure I'll just chip away at it a piece at a time.  
> 
> This seems like the right time to ask if anyone else is having a go at it, or wants to give me a hand.  I've actually just got a job (yay me) but wont start for a bit (11th June) so I have some spare time.  Once I start work I wont have as much time so it would be good to find someone else who can help.
> 
> In the meantime I have reached a point where a type PQ_64BIT is used.  Looking at the headers it appears this type is defined differently for each system/compiler based on whether they have a 64 bit type, so on windows using M$ compilers etc it is __int64 for example.  In the rest of cases it is a custom BIGNUM struct.
> 
> My question is this.. what the heck do I put in my D port when I see this type used?
> 
> In D, long is a 64 bit type, but... I'm not writing new code I am writing a wrapper so I need to put the actual type the C library is using (was compiled using), otherwise any struct using PQ_64BIT might be the wrong size and disastrous things might happen.
> 
> Am I understanding this correctly?
> 
> It seems that I can probably get away with swapping PQ_64BIT for long in the short term, as I suspect my library was compiled with a 64bit type, not the BIGNUM struct...
> 
> Thoughts?

Having a very quick poke around the OpenSSL docs, it looks like PQ_64BIT
is designed to be used as an opaque type.  The problem, of course, is
that you don't know how the library was compiled.

It looks like the only safe way to do it is to mimic the C headers.
Something like this:

version( SIXTY_FOUR_BIT )
{
    typedef ulong PQ_64BIT; // Note that I think OpenSSL uses ulongs!
    void pq_64bit_init(ref PQ_64BIT x) {}
    void pq_64bit_add_word(ref PQ_64BIT x, ref PQ_64BIT w) {x += w}
}
else
{
    typedef BIGNUM PQ_64BIT;
    void pq_64bit_init(ref PQ_64BIT x) { BN_INIT(&x); }
    void pq_64bit_add_word(ref PQ_64BIT x, ref PQ_64BIT w) {
BN_add_word(&x, &w); }
}

And so on.  Ugly as hell, but that's how OpenSSL is doing things.

Hope that's of some help :P

	-- Daniel

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