[racket] FFI bitfields

At Sun, 09 Jun 2013 21:42:47 +0400, Клочков Роман wrote:
>  How to make in Racket FFI struct with bit fields
> For example, such struct
> 
> struct box_props
> {
>      unsigned int opaque       : 1;
>      unsigned int fill_color   : 3;
>      unsigned int              : 4; // fill to 8 bits
>      unsigned int show_border  : 1;
>      unsigned int border_color : 3;
>      unsigned int border_style : 2;
>      unsigned int              : 2; // fill to 16 bits
> };
> 
> ?

The `ffi/unsafe' library currently doesn't include support for
bitfields. I think you have to declare a structure with an integer and
use operations like `arithmetic-shift' and `bitwise-and' to manipulate
bits in the integer.