On Thursday, 2 August 2012 at 09:14:15 UTC, Era Scarecrow wrote:
On Thursday, 2 August 2012 at 09:03:54 UTC, monarch_dodra wrote:
I had an (implementation) question for you: Does the
implementation actually require knowing what the size of the
padding is?
eg:
struct A
{
int a;
mixin(bitfields!(
uint, "x", 2,
int, "y", 3,
ulong, "", 3 // <- This line right there
));
}
It that highlighted line really mandatory?
I'm fine with having it optional, in case I'd want to have,
say, a 59 bit padding, but can't the implementation figure it
out on it's own?
The original code has it set that way, why? Perhaps so you are
aware and actually have in place where all the bits are
assigned (even if you aren't using them); Be horrible if you
used accidently 33 bits and it extended to 64 without telling
you (Wouldn't it?).
However, having it fill the size in and ignore the last x bits
wouldn't be too hard to do, I've been wondering if I should
remove it.
Well, I was just trying to figure out the rationale: The most
obvious one for me being "it is much easier on the
implementation".
One of the *big* reasons I'm against having a hand chosen
padding, is that the implementation *should* be able to find out
what the most efficient padding is on the current machine (could
be 32 on some, could be 64 on some)
That said, something that could fix the above "problem" could be:
*Bitfields are automatically padded if the final field is not a
"padding field".
**Padding size is implementation chosen.
*If the final field is a "padding field", then the total size
must be 8/16/32/64.
EG:
//Case 1
bitfields!(
bool, "x", 1,
uint, "", 3, //Interfield padding
bool, "y", 1
)
//Fine, implementation chosen bitfield size
//Case 2
bitfields!(
bool, "x", 1,
uint, "", 3, //Interfield padding
bool, "y", 1
ulong, "", 59, //Pad to 64
)
//Fine, imposed 64 bit
//Case 3
bitfields!(
bool, "x", 1,
uint, "", 3, //Interfield padding
bool, "y", 1
ulong, "", 32, //Pad to 37
)
//ERROR: Padding requests the bitfield to be 37 bits longs
But I'd say that's another development anyways, if we ever decide
to go this way.
