add pffft

pffft/examples/example_cpp11_cplx_dbl_fwd.cpp

@@ -0,0 +1,66 @@
+
+#include "pffft.hpp"
+
+#include <complex>
+#include <iostream>
+
+
+void cxx11_forward_complex_double(const int transformLen)
+{
+  std::cout << "running " << __FUNCTION__ << "()" << std::endl;
+
+  // first check - might be skipped
+  using FFT_T = pffft::Fft< std::complex<double> >;
+  if (transformLen < FFT_T::minFFtsize())
+  {
+    std::cerr << "Error: minimum FFT transformation length is " << FFT_T::minFFtsize() << std::endl;
+    return;
+  }
+
+  // instantiate FFT and prepare transformation for length N
+  pffft::Fft< std::complex<double> > fft(transformLen);
+
+  // one more check
+  if (!fft.isValid())
+  {
+    std::cerr << "Error: transformation length " << transformLen << " is not decomposable into small prime factors. "
+              << "Next valid transform size is: " << FFT_T::nearestTransformSize(transformLen)
+              << "; next power of 2 is: " << FFT_T::nextPowerOfTwo(transformLen) << std::endl;
+    return;
+  }
+
+  // allocate aligned vectors for input X and output Y
+  auto X = fft.valueVector();
+  auto Y = fft.spectrumVector();
+
+  // alternative access: get raw pointers to aligned vectors
+  std::complex<double> *Xs = X.data();
+  std::complex<double> *Ys = Y.data();
+
+  // prepare some input data
+  for (int k = 0; k < transformLen; k += 2)
+  {
+    X[k] = std::complex<double>(k, k&1);        // access through AlignedVector<double>
+    Xs[k+1] = std::complex<double>(-1-k, k&1);  // access through raw pointer
+  }
+
+  // do the forward transform; write complex spectrum result into Y
+  fft.forward(X, Y);
+
+  // print spectral output
+  std::cout << "output should be complex spectrum with " << fft.getSpectrumSize() << " bins" << std::endl;
+  std::cout << "output vector has size " << Y.size() << " (complex bins):" << std::endl;
+  for (unsigned k = 0; k < Y.size(); k += 2)
+  {
+    std::cout << "Y[" << k << "] = " << Y[k] << std::endl;
+    std::cout << "Y[" << k+1 << "] = " << Ys[k+1] << std::endl;
+  }
+}
+
+
+int main(int argc, char *argv[])
+{
+  int N = (1 < argc) ? atoi(argv[1]) : 16;
+  cxx11_forward_complex_double(N);
+  return 0;
+}