***BOGO*** Re: [Mingw-users] MinGW with SIMD (SSE, etc)

[Dustin McCartney <dustin.mccartney.public@xxxxxxxxx>]

> Dustin,
> 
> If you really want to take advantage of aligned data, you should 
> allocate all the data you will use with SSE in the C/C++ side, then just 
> send a pointer via a FloatBuffer/ByteBuffer to Java. That way, you only 
> have to work with pointers between the two, and they will aways point to 
> aligned data. Any POD structure that have a intrinsic variable (union, 
> struct) will be aligned automatically by the compiler even if you use 
> new/malloc so I think that's the way you will get the most performance. 
> That's what I do in my C++ code and I never had any issue using movaps.
> 
> I don't know how to send that pointer via FloatBuffer to Java as I have 
> never done that before but I think it's not that difficult.
> 
> best,
> 
> Rafael

Actually, I am not sharing any of the data that uses SSE with Java via
JNI.  I am using Java simply as a "controller" that tells the C/C++ code
when to do what (which the Java controller can invoke in concurrent
threads).

My current problem is that I have a Vector3 class defined as such (with
defines for MinGW/GCC):

#define PFX_EXPORT __stdcall
#define ALIGN16_BEG
#define ALIGN16_END __attribute__ ((aligned(16)))
#define ALIGN_STACK __attribute__ ((force_align_arg_pointer))

struct PFX_EXPORT Vector3 ALIGN16_BEG
{
  union
  {
    ALIGN16_BEG v4sf v ALIGN16_END;
    struct ALIGN16_BEG 
    {
        float x, y, z, w;
    } ALIGN16_END;
  } ALIGN16_END;

  PFXAPI Vector3() ALIGN_STACK {}

  PFXAPI Vector3(bool bInit) ALIGN_STACK
  {
    if (bInit)
    {
      v = _mm_setzero_ps();
      _mm_empty();
    }
  }

  PFXAPI Vector3(const Vector3 & other) ALIGN_STACK
  {
    v = other.v;
    _mm_empty();
  }

  PFXAPI Vector3(float fX, float fY, float fZ) ALIGN_STACK
  {
    v = _mm_set_ps( fX, fY, fZ, 0.0f );
    _mm_empty();
  }
  ...
  float PFXAPI Length() const ALIGN_STACK
  {
    Vector3 tmp;
    tmp.v = _mm_mul_ps( v, v );
    _mm_empty();
    return sqrtf( tmp.x + tmp.y + tmp.z );
  }
  ...
};

I use Vector3 in various other objects such as:
struct PFX_EXPORT Foo
{
  Vector3 m_v3Test;
};

SegFaults occur when the Vector3 object functions (such as the
constructors) are called, as the Vector3 member variable "v" is not
aligned on 16 byte boundaries.  This has been driving me crazy.  :-P

Dustin


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