__declspec(align(16)) for btr

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how do i align the btr data before manupulations in sse2? see code snippet below

C++

//.h file
Class tom
{
Public:
virtual void add(void* btr);
.
.
.
}

// .cpp file

void tom::add(void* btr)
{
    int* b = (int *)btr;
}

Posted 6-Aug-10 1:08am

SMART LUBOBYA

Updated 6-Aug-10 1:10am

Sauro Viti

v2

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Sauro Viti · Answer 1 · 2010-08-06T01:15:00

Solution 1

It doesn't matter if btr is not aligned, what is important is that the buffer pointed by it is aligned (i.e. the address inside btr should be aligned). After that use the statement:

C++

__declspec(aligned(16)) int *b = (int *)btr;

Posted 6-Aug-10 1:15am

Sauro Viti

Comments

SMART LUBOBYA 6-Aug-10 7:34am

sauro, thanks for your quick response. btr is an array of integers. just how do i do address alignment?

Sauro Viti 6-Aug-10 7:44am

This way:

void DoSomethingWithSSE2(int *btr)
{
// btr is an address passed on the stack, the parameter address could not be aligned...
__declspec(align(16)) int *b = btr; // This way the address of b is aligned!
}

void main()
{
// The array should be aligned for use with SSE2
__declspec(align(16)) int array[4][4] = { ... };

DoSomethingWithSSE2(array);
}

SMART LUBOBYA 6-Aug-10 10:02am

in my code where do i place this:
void DoSomethingWithSSE2(int *btr) { // btr is an address passed on the stack, the parameter address could not be aligned... __declspec(align(16)) int *b = btr; // This way the address of b is aligned! }
in .h file or .cpp file?

Sauro Viti 6-Aug-10 14:22pm

As that function is not declared as inline, you should place it in a .cpp file: if you place it in a .h file and then you include the header from more than one .cpp file ou will get warnings/errors while linking

SMART LUBOBYA 8-Aug-10 5:31am

tried this:
//.cpp file

void tom::add(void* btr)
{
void add(int *btr)
{ //error C2601: 'add' : local function definitions are illegal
__declspec(align(16)) int *b = btr;
}

__declspec(align(16))int* b =(int*)btr;
__m128i f0,f1,f2,f3;
f0 = _mm_loadu_si128((__m128i*)b);
f1 = _mm_loadu_si128((__m128i*)b+1);
f2 = _mm_loadu_si128((__m128i*)b+2);
f3 = _mm_loadu_si128((__m128i*)b+3);
}
i get error C2601: 'add' : local function definitions are illegal

Sauro Viti 9-Aug-10 2:20am

why did you define a function inside another one? in C/C++ is illegal: remove the add() function and I think that everything will go ok!