suppose i have a struct on the host as follows:
typedef struct{
float x;
float y;
float z;
} FloatThree __attribute__ ((aligned (4)));
typedef struct
{
uint u;
int i;
float f;
FloatThree ft;
char c;
}Params __attribute__ ((aligned (16)));
is it necessary to add padding/alignment? Section 5.1 in the AMD beta4 release notes says that structs must be packed and aligned. I see section 6.10.1 in the spec which states:
Note that the alignment of any given struct or union type is required by the ISO C standard to be at least a perfect multiple of the lowest common multiple of the alignments of all of the members of the struct or union in question and must also be a power of two.
For FloatThree each member is 4 bytes, so the LCM is 4 bytes, which is a power of 2.. so an alignment of 4 seems correct.
For Params the first 3 members are 4 bytes each, the struct is 12 bytes (it is aligned to 4) and the char is 1 byte. According to 6.1.5 the char must be aligned to two bytes. So the LCM would seem to be 12 and the alignment is the next highest power of 2 which is 16. But it seems based on the 5.1 release notes example that i need to explicitly add padding:
typedef struct
{
uint u;
int i;
float f; // 12 bytes up to here
char pad1[4]; // now 16
FloatThree ft; // another 12 bytes
char c; // 1 byte
char pad[3]; // now 16
}Params __attribute__ ((aligned (16)));
Does this seem correct? I think if it's wrong it could conceivably cause at least some of issues i'm seeing.
