Re: GSoC-2011: Implement Missing Mesh Functions in Wine’s D3DX9

max max at
Thu Aug 4 07:30:41 CDT 2011

On 08/03/2011 09:28 AM, Henri Verbeet wrote:
> Well yes, it's implementation defined, not undefined. The point is
> that there isn't necessarily any relation to endianness. Just use
> shifts and masks.

Correct. It is a different issue from endedness.

But you can use configurable wrappers to cloak the compiler differences:

Meta procedure:

1) Write a test to determine which order bit fields are assigned in:

int main(){
     union field_order { int an_int; int a_bit:1 } test;
     return test.an_int == 1;

which returns 0 if bit fields are allocated most significant bits
first, 1 otherwise.

2) Add a test to configure that checks the field allocation order.
Record the result of the test as LO_ORDER_FIRST or something.

3) Write some macros that hide the declaration order:

#define BIT_FIELDS_2(a,b) a;b;
#define BIT_FIELDS_3(a,b,c) a;b;c;
#define BIT_FIELDS_4(a,b,c,d) a;b;c;d;
#define BIT_FIELDS_2(a,b) b;a;
#define BIT_FIELDS_3(a,b,c) c;b;a;
#define BIT_FIELDS_4(a,b,c,d) d;c;b;a;

4) Constraint: The combined fields must have the same number of bits
as the underlying data type. For example, if 'int' has 32 bits, the total
size of all the fields in the group must be 32 bits.

THIS HAS PROBABLY BEEN DONE ALREADY!, you just have to dig it out
of the list of available configure tests.


(I'm in the middle of something else, otherwise, I'd dig it out myself...)

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