On 8/30/2021 12:40 PM, Paul Backus wrote:
> On Monday, 30 August 2021 at 18:39:20 UTC, Walter Bright wrote:
>> On 8/29/2021 11:32 PM, Elronnd wrote:
>>> On Saturday, 28 August 2021 at 08:20:25 UTC, Walter Bright wrote:
>>>> how gcc/clang do it is essentially undocumented
>>>
>>> x86-64-psABI, sec 3.1.2 (data representation)
>>
>> https://github.com/hjl-tools/x86-psABI/wiki/x86-64-psABI-1.0.pdf
>>
>> That only partially documents it. It doesn't cover things like alignment and 0 length fields.
> 
> Zero-length bitfields are covered by the C standard:
> 
>> As a special case, a bit-field structure member with a width of 0 indicates that no further bit-field is to be packed into the unit in which the previous bit-field, if any, was placed.
> 
> Source: http://port70.net/~nsz/c/c99/n1256.html#6.7.2.1p11

Doesn't cover alignment, either. Doesn't cover what happens with a struct where the only member is a 0 bit field. Doesn't cover what a sequence of 2 or more 0 bit fields does.

On 8/30/2021 3:45 PM, TheGag96 wrote:
> I think I may be experiencing a bug in a betterC project of mine as a result of me assuming that `bitfields` is doing the same thing as gcc would...! Is there a way I can get things synced up on at least one platform in the meantime?

The ImportC bit fields will be in the next dmd beta.

Until D itself gets bit fields, the thing to do will be to declare the bit field struct in a separate .c file, and import it.

Otherwise, the only way is to implement your own using get/set member functions.

On 8/30/2021 6:04 PM, Paul Backus wrote:
> Don't use bitfields for anything that needs to have a stable ABI. They're not even guaranteed to have the same layout when using the same compiler on different platforms [1], much less between different languages.

Things are pretty consistent if sticking with simple int/unsigned bit fields.