Quick start#

The following code is a simplified version of 1d_c2c_single_example.cpp available from NVPLSamples, showing how to use NVPL FFT.

#include <iostream>
#include <vector>
#include <complex>
#include <nvpl_fftw.h>

int main(int argc, char *argv[]) {
    const int n = 4;
    const int howmany = 2;

    std::vector<std::complex<float>> in(howmany * n);
    std::vector<std::complex<float>> out(howmany * n);

    fftwf_complex *in_data  = reinterpret_cast<fftwf_complex*>(in.data() );
    fftwf_complex *out_data = reinterpret_cast<fftwf_complex*>(out.data());

    fftwf_plan plan = fftwf_plan_dft_1d(n, in_data, out_data, FFTW_FORWARD, FFTW_ESTIMATE);

    int i = 0;
    for (auto& v: in) {
        v = {(float)i, -(float)i};
        i++;
    }

    for(int b = 0; b < howmany; b++) {
        fftwf_execute_dft(plan, in_data+b*n, out_data+b*n);
    }

    for (const auto& v: out) {
        std::cout << v << "\n";
    }

    fftwf_destroy_plan(plan);
    fftwf_cleanup();
    return 0;
}

This example computes howmany batches of a one-dimensional forward FFT with size n. It does the following:

  1. Allocates the input and output data

  2. Creates a 1D FFTW plan with specified size n and transform direction FFTW_FORWARD

  3. Initializes the input data.

  4. Executes the plan. One batch at a time.

  5. Outputs the results.

  6. Destroys the plan.

The example can then be compiled and run as follows:

$ g++ app.cpp -I/path/to/nvpl_fft/include -L/path/to/nvpl_fft/lib -lnvpl_fftw -o app
$ ./app
(6,-6)
(0,4)
(-2,2)
(-4,0)
(22,-22)
(0,4)
(-2,2)
(-4,0)

Note

Starting from NVPL FFT 0.4.0, NVPL FFT provides a copy of nvpl_fftw.h, renamed to fftw3.h, under a new header path: /path/to/nvpl_fft/include/nvpl_fftw. This path has been added to the CMake build files so no changes are required when building with CMake. If building without CMake, the new header path can be made visible by either updating the include path or through CPATH (i.e. CPATH=<prefix>/include/nvpl_fftw:$CPATH)

Tip

For an application that dynamically links to the FFTW3 libraries, one could test NVPL FFT by running the application with LD_PRELOAD=/path/to/nvpl_fft/lib/libnvpl_fftw.so.