SIMD或非SIMD - 跨平台 [英] SIMD or not SIMD - cross platform
问题描述
我需要一些想法如何编写一个C ++跨平台实现的几个可并行化的问题,以便我可以利用SIMD(SSE,SPU等)(如果可用)。
I need some idea how to write a C++ cross platform implementation of a few parallelizable problems in a way so I can take advantage of SIMD (SSE, SPU, etc) if available. As well as I want to be able at run time to switch between SIMD and not SIMD.
我希望能在运行时在SIMD和非SIMD之间切换。 >
(当然我不想多次实现所有可能的选项)
How would you suggest me to approach this problem? (Of course I don't want to implement the problem multiple times for all possible options)
我可以看到这可能不是很容易的任务与C ++,但我相信,我错过了一些东西。到目前为止我的想法看起来像这样...
类cStream将是一个字段的数组。使用多个cStreams我可以实现SoA(数组的结构)。然后使用几个Functors,我可以伪造Lambda函数,我需要在整个cStream上执行。
I can see how this might not be very easy task with C++ but I believe that I'm missing something. So far my idea looks like this... A class cStream will be array of a single field. Using multiple cStreams I can achieve SoA (Structure of Arrays). Then using a few Functors I can fake Lambda function that I need to be executed over the whole cStream.
// just for example I'm not expecting this code to compile
cStream a; // something like float[1024]
cStream b;
cStream c;
void Foo()
{
for_each(
AssignSIMD(c, MulSIMD(AddSIMD(a, b), a)));
}
其中for_each将负责增加流的当前指针,
Where for_each will be responsible for incrementing the current pointer of the streams as well as inlining the functors' body with SIMD and without SIMD.
像这样:
// just for example I'm not expecting this code to compile
for_each(functor<T> f)
{
#ifdef USE_SIMD
if (simdEnabled)
real_for_each(f<true>()); // true means use SIMD
else
#endif
real_for_each(f<false>());
}
请注意,如果SIMD被启用检查一次,主要函数。
Notice that if the SIMD is enabled is checked once and that the loop is around the main functor.
推荐答案
如果有人感兴趣,这是脏代码,我来测试一个新的想法,同时阅读Paul发布的图书馆。
If someone is interested this is the dirty code I come with to test a new idea that I came with while reading about the library that Paul posted.
感谢Paul!
// This is just a conceptual test
// I haven't profile the code and I haven't verified if the result is correct
#include <xmmintrin.h>
// This class is doing all the math
template <bool SIMD>
class cStreamF32
{
private:
void* m_data;
void* m_dataEnd;
__m128* m_current128;
float* m_current32;
public:
cStreamF32(int size)
{
if (SIMD)
m_data = _mm_malloc(sizeof(float) * size, 16);
else
m_data = new float[size];
}
~cStreamF32()
{
if (SIMD)
_mm_free(m_data);
else
delete[] (float*)m_data;
}
inline void Begin()
{
if (SIMD)
m_current128 = (__m128*)m_data;
else
m_current32 = (float*)m_data;
}
inline bool Next()
{
if (SIMD)
{
m_current128++;
return m_current128 < m_dataEnd;
}
else
{
m_current32++;
return m_current32 < m_dataEnd;
}
}
inline void operator=(const __m128 x)
{
*m_current128 = x;
}
inline void operator=(const float x)
{
*m_current32 = x;
}
inline __m128 operator+(const cStreamF32<true>& x)
{
return _mm_add_ss(*m_current128, *x.m_current128);
}
inline float operator+(const cStreamF32<false>& x)
{
return *m_current32 + *x.m_current32;
}
inline __m128 operator+(const __m128 x)
{
return _mm_add_ss(*m_current128, x);
}
inline float operator+(const float x)
{
return *m_current32 + x;
}
inline __m128 operator*(const cStreamF32<true>& x)
{
return _mm_mul_ss(*m_current128, *x.m_current128);
}
inline float operator*(const cStreamF32<false>& x)
{
return *m_current32 * *x.m_current32;
}
inline __m128 operator*(const __m128 x)
{
return _mm_mul_ss(*m_current128, x);
}
inline float operator*(const float x)
{
return *m_current32 * x;
}
};
// Executes both functors
template<class T1, class T2>
void Execute(T1& functor1, T2& functor2)
{
functor1.Begin();
do
{
functor1.Exec();
}
while (functor1.Next());
functor2.Begin();
do
{
functor2.Exec();
}
while (functor2.Next());
}
// This is the implementation of the problem
template <bool SIMD>
class cTestFunctor
{
private:
cStreamF32<SIMD> a;
cStreamF32<SIMD> b;
cStreamF32<SIMD> c;
public:
cTestFunctor() : a(1024), b(1024), c(1024) { }
inline void Exec()
{
c = a + b * a;
}
inline void Begin()
{
a.Begin();
b.Begin();
c.Begin();
}
inline bool Next()
{
a.Next();
b.Next();
return c.Next();
}
};
int main (int argc, char * const argv[])
{
cTestFunctor<true> functor1;
cTestFunctor<false> functor2;
Execute(functor1, functor2);
return 0;
}
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