add pffft

pffft/examples/example_c_real_flt_fwd.c

@@ -0,0 +1,66 @@
+
+#include "pffft.h"
+
+#include <stdio.h>
+#include <stdlib.h>
+
+
+void c_forward_real_float(const int transformLen)
+{
+  printf("running %s()\n", __FUNCTION__);
+
+  /* first check - might be skipped */
+  if (transformLen < pffft_min_fft_size(PFFFT_REAL))
+  {
+    fprintf(stderr, "Error: minimum FFT transformation length is %d\n", pffft_min_fft_size(PFFFT_REAL));
+    return;
+  }
+
+  /* instantiate FFT and prepare transformation for length N */
+  PFFFT_Setup *ffts = pffft_new_setup(transformLen, PFFFT_REAL);
+
+  /* one more check */
+  if (!ffts)
+  {
+    fprintf(stderr,
+            "Error: transformation length %d is not decomposable into small prime factors. "
+            "Next valid transform size is: %d ; next power of 2 is: %d\n",
+            transformLen,
+            pffft_nearest_transform_size(transformLen, PFFFT_REAL, 1),
+            pffft_next_power_of_two(transformLen) );
+    return;
+  }
+
+  /* allocate aligned vectors for input X and output Y */
+  float *X = (float*)pffft_aligned_malloc(transformLen * sizeof(float));
+  float *Y = (float*)pffft_aligned_malloc(transformLen * sizeof(float));  /* complex: re/im interleaved */
+  float *W = (float*)pffft_aligned_malloc(transformLen * sizeof(float));
+
+  /* prepare some input data */
+  for (int k = 0; k < transformLen; k += 2)
+  {
+    X[k] = k;
+    X[k+1] = -1-k;
+  }
+
+  /* do the forward transform; write complex spectrum result into Y */
+  pffft_transform_ordered(ffts, X, Y, W, PFFFT_FORWARD);
+
+  /* print spectral output */
+  printf("output should be complex spectrum with %d complex bins\n", transformLen /2);
+  for (int k = 0; k < transformLen; k += 2)
+    printf("Y[%d] = %f + i * %f\n", k/2, Y[k], Y[k+1]);
+
+  pffft_aligned_free(W);
+  pffft_aligned_free(Y);
+  pffft_aligned_free(X);
+  pffft_destroy_setup(ffts);
+}
+
+
+int main(int argc, char *argv[])
+{
+  int N = (1 < argc) ? atoi(argv[1]) : 32;
+  c_forward_real_float(N);
+  return 0;
+}