参考文档：https://docs.nvidia.com/cuda/cufft/index.html
这一篇写的很详细：
https://blog.csdn.net/endlch/article/details/46724811
原图像存为一维float型数组后cpy到GPU上，按列进行fft操作。
高度优化后的算法可以支持格式为2a*3b*5c*7d的输入大小。
支持三种类型，C2C,R2C,C2R
同时执行多个1D、2D和3D变换。这些成批转换比单个转换具有更高的性能。
任意内部维度元素的步长 Arbitrary intra- and inter-dimension element strides (strided layout)
提供一个句柄 Plan 当用户创建plan时，库保留多次执行plan所需的任何状态，而无需重新计算配置。
cuFFT provides a simple configuration mechanism called a plan that uses internal building blocks to optimize the transform for the given configuration and the particular GPU hardware selected. Then, when the execution function is called, the actual transform takes place following the plan of execution. The advantage of this approach is that once the user creates a plan, the library retains whatever state is needed to execute the plan multiple times without recalculation of the configuration. This model works well for cuFFT because different kinds of FFTs require different thread configurations and GPU resources, and the plan interface provides a simple way of reusing configurations.
第一步： 用以下的 函数创建 plan
cufftPlan1D() / cufftPlan2D() / cufftPlan3D() - Create a simple plan for a 1D/2D/3D transform respectively.
cufftPlanMany() - 批量输入 Creates a plan supporting batched input and strided data layouts.
cufftXtMakePlanMany() - Creates a plan supporting batched input and strided data layouts for any supported precision.
第二步：call an execution function
cufftExecC2C()
In the case of general complex-to-complex transform both the input and output data shall be a cufftComplex/cufftDoubleComplex array in single- and double-precision modes respectively.
R2C demands an input array ( X 1 , X 2 , … , X N ) of real values and returns an array ( x 1 , x 2 , … , x ⌊ N 2 ⌋ + 1 ) of non-redundant complex elements.
Once the plan is no longer needed, the cufftDestroy() function should be called to release the resources allocated for the plan.
关于数据布局：
R2C和C2R变化前后数据的大小是不一样的。
For out-of-place transforms a separate array of appropriate size is created.
For in-place transforms the user should use padded data layout. This layout is FFTW compatibile.
在补充布局中，输出信号内存的开始位置与输入信号的一样，因此R2C模式必须对输入数据进行补零。In the padded layout output signals begin at the same memory addresses as the input data. Therefore input data for real-to-complex and output data for complex-to-real must be padded.
相关参数设定：
The istride and ostride parameters denote the distance between two successive input and output elements in the least significant (that is, the innermost) dimension respectively.
用来设定两个连续的输入/输出数据间的步长。
In a single 1D transform, if every input element is to be used in the transform, istride should be set to 1 ; if every other input element is to be used in the transform, then istride should be set to 2 . Similarly, in a single 1D transform, if it is desired to output final elements one after another compactly, ostride should be set to 1 ; if spacing is desired between the least significant dimension output data, ostride should be set to the distance between the elements.
The inembed and onembed parameters define the number of elements in each dimension in the input array and the output array respectively. 定义输入/输出数组每个维度的大小
The idist and odist parameters indicate the distance between the first element of two consecutive batches in the input and output data.
All cuFFT Library return values except for CUFFT_SUCCESS indicate that the current API call failed and the user should reconfigure to correct the problem. The possible return values are defined as follows:
#define NX 256
#define BATCH 10
#define RANK 1
...
{ cufftHandle plan;
cufftComplex *data;
...
cudaMalloc((void**)&data,sizeof(cufftComplex)*NX*BATCH);
cufftPlanMany(&plan, RANK, NX, &iembed, istride, idist, &oembed, ostride, odist, CUFFT_C2C, BATCH);
...
cufftExecC2C(plan, data, data, CUFFT_FORWARD);
cudaDeviceSynchronize();
...
cufftDestroy(plan);
cudaFree(data);
}
The istride and ostride parameters denote the distance between two successive input and output elements in the least significant (that is, the innermost) dimension respectively. In a single 1D transform, if every input element is to be used in the transform, istride should be set to 1 ; if every other input element is to be used in the transform, then istride should be set to 2 . Similarly, in a single 1D transform, if it is desired to output final elements one after another compactly, ostride should be set to 1 ; if spacing is desired between the least significant dimension output data, ostride should be set to the distance between the elements.
