* Michael D. Adams wrote:
But as far as I can tell, hsc2hs doesn't support bit fields. On top of that I'm not sure I can make any safe assumptions about what order the bit fields are packed (LSB or MSB first).
C standard allows padding and reorder of struct entries in order to match alignment requirements. The only exeption are bitfields, which must not reordered and padded. This way bit fields are the only portable way to define the binary representation in C. Unfortunly the C standard does not specify any bit order for bit fields, but almost all implementations use the machine specific bit order, in order to ease access to multiple bits wide bit field and fill LSB to MSB. But there is no guarantee. I run into this problem when writing an low level kernel interface in SPARK. The ABI (binary representation) of the kernel API depends on the C compiler flags (i.e. #pragma packed). Especially kernels of commericial unicies might generate this problem, because the developer uses gcc instead of the native compiler. The only portable way to get access to C defined structures is involving a C compiler, either using hsc or a C helper module.