topic how aligned class data member, in Intel® ISA Extensions

how aligned class data member,

Timocafe — Wed, 27 Oct 2010 10:16:11 GMT

Hello All,

I am implemented a unlimited integer class, and I used SIMD to calculate basic operation + *.

At the beginning I developed a single kernel to test my code, and I declared and aligned my data

in the main by the __attribute__((aligned(16))) command, it works. Now I am writing

a basic class, nevertheless the command__attribute__((aligned(16))) does not align (why) my array

and so the code crash when I run it.

Any idea to align a basic array on 16 bytes boundary as data member of a class.

Thanks

Tim

how aligned class data member,

Nicolae_P_Intel — Wed, 27 Oct 2010 10:36:04 GMT

could you please re-check your post?your question is somehow missing (or not displayed properly).

how aligned class data member,

Timocafe — Wed, 27 Oct 2010 10:38:56 GMT

Done, I do not why it does not work the first time !

how aligned class data member,

Timocafe — Wed, 27 Oct 2010 11:06:02 GMT

I find I make a typo on my kernel, sorry.

how aligned class data member,

Nicolae_P_Intel — Wed, 27 Oct 2010 13:52:37 GMT

can you share what typo have you find?
what compiler are you using and which platform? 64 or 32 bit?
what compiler options?

how aligned class data member,

Matthias_Kretz — Wed, 27 Oct 2010 19:47:38 GMT

Hi,

note that __attribute__((aligned(16))) only works for allocation on the stack. When you allocate a type defined with that attribute on the heap (i.e. new/malloc) then the alignment restriction of the attribute does not apply. Instead you should rather use _mm_malloc with the correct alignment parameter.

It is possible to overload the new and delete operators of the class to achieve the desired effect automatically:

void *operator new(size_t size) { return _mm_malloc(size, alignment); }

void *operator new[](size_t size) { return _mm_malloc(size, alignment); }

void operator delete(void *ptr, size_t) { _mm_free(ptr); }

void operator delete[](void *ptr, size_t) { _mm_free(ptr); }

how aligned class data member,

Timocafe — Fri, 29 Oct 2010 12:11:02 GMT

Thank you very much for these informations, I did not know about __attribute__((aligned(16))) runs only in the stack. No problem to overload the operator, great solution !

Thank you

Tim

how aligned class data member,

Gaiger_Chen — Fri, 19 Nov 2010 07:30:59 GMT

By the way, if your platform is windows , use :

_aligned_malloc / _aligned_free

to allocate aligned memory.

how aligned class data member,

Matthias_Kretz — Mon, 22 Nov 2010 18:16:53 GMT

If you can use _mm_malloc, then please don't use windows specific API for the sake of portability. The only real standard way of allocating aligned memory on the heap probably is posix_memalign (sadly Windows doesn't offer POSIX compat per default, though). So using the _mm_ intrinsics probably comes closest to a portable standard...

how aligned class data member,

Gaiger_Chen — Fri, 24 Dec 2010 10:02:19 GMT

Hi

quick solution : use

_mm_loadu_si128 / _mm_storeu_si128

to replase

_mm_load_si128 and _mm_store_si128

it should be pass.

(the __attribute__((aligned(16))) could be remove also.)