C/C++ Aligned allocation and VC++.NET

[Dissident Dan]

Has anyone else experience the new operator not working correctly for 16-byte aligned data types? I am using Visual Studio .NET 2003.

I have a class that has its first component 16 byte-aligned via the "__declspec(align(16))" directive because I am using SSE.

class Vector {
public:
// data members
union {
__declspec(align(16)) float comps[4];
struct {
float x,y,z,w;
};
struct {
float r, g, b, a;
};
struct {
float yaw, pitch, roll;
};
};

When dynamically allocating and array of this class using the new operator, I get an 8 byte-aligned pointer. It needs to be 16 byte-aligned to not crash when using SSE intrinsics.

I have even tried using "__declspec(align(16))" on the pointer and between the "new" and the data type. Example:

__declspec(align(16)) Vector *tan1 = new __declspec(align(16)) Vector[vertexCount * 2];

I have resorted to using the old C functions _aligned_malloc() and _aligned_free().

This must be a bug with Visual Studio, right? Anyone know of any fixes?

 

[dduardo]

You're probably going to need to post this on a microsoft newsgroup or forum. I'm not familiar with MS specific code. In gcc __attribute__ (aligned(16)) is used.

[edit] This is just a guess, but when using __attribute__ I believe it goes after the allocation statement. Something like this:

float comps[4] __attribute__ (aligned(16));

This might be the same case with __delcspec

 

[Dissident Dan]

It turns out that you need to overload the new and delete operators using aligned malloc and free functions.

Check out this PDF for more info:
http://homepage.te.hik.se/personal/tkama/audio_procME/papers/17664_alignment.pdf"

 

[adrean87]

huh?

 

[zyh]

The help file( CHM ) supplied by intel c++ compiler hase some example on this topic. Also, www.codeproject.com hase some articles to introduce SSE.