Re: [Chicken-users] working with bit- and byte-level structures

[john]

The idea behind packedobjects is to be able to use an abstract syntax
for describing what gets bit packed into messages to be sent across a
network. The syntax is loosely based on ASN.1 but uses s-expressions
to avoid the need for an ASN.1 compiler. The encoding is based on
unaligned Packed Encoding Rules (PER). So if you are looking at
packing data into messages in a machine independent way it might be
useful.

Cheers,

John.

On 16/04/2008, Martin DeMello <address@hidden> wrote:
> Interesting post on one of the advantages of C++ - I just wondered how
>  such problems are handled in the scheme world
>
>  
> ------------------------------------------------------------------------------------------------------
>  What you can do in C++ that you *can't* do in Java is define a class
>  whose in-memory representation maps directly to the format of data in
>  memory, and then say "I want to treat this large swath of memory as if
>  it were an array of Foo objects" - and gain all of the abstraction of
>  calling object methods on that data, with zero performance penalty for
>  instantiating thousands of objects.
>
>  It's not something you want to do every day, but on the rare occasion
>  you need it, C++ comes closest to letting you have your cake and eat
>  it too.
>
>  -- Avdi Grimm on the pragmaticprogrammers mailing list
>  
> ------------------------------------------------------------------------------------------------------
>
>  I ran into this exact problem when trying to access a packed C data
>  structure from OCaml - I had to write a bunch of code to index into
>  the block, pull out a chunk of bytes and then write accessor functions
>  to do bitshifting and bitmasking to retrieve the individual members
>  from the struct, without much "higher level" help from OCaml. I'm
>  imagining some combination of C and chicken would do a nicer job of
>  this, and naturally I'd want to do it with as little C as possible. I
>  found http://chicken.wiki.br/packedobjects but I couldn't tell if it
>  could work directly with a block of memory or it there'd be a lot of
>  from/to overhead.
>
>  martin
>
>
>  _______________________________________________
>  Chicken-users mailing list
>  address@hidden
>  http://lists.nongnu.org/mailman/listinfo/chicken-users
>