diff --git a/src/tests/fftw3_bare/fftw3_test.cpp b/src/tests/fftw3_bare/fftw3_test.cpp
index fbdefa67..40457a56 100644
--- a/src/tests/fftw3_bare/fftw3_test.cpp
+++ b/src/tests/fftw3_bare/fftw3_test.cpp
@@ -3,41 +3,72 @@
 
 #include <fftw3.h>
 
-int main(int argc, char *argv[]) {
-    const unsigned int N=8192;
-    
-    fftw_complex *in, *out;
-    fftw_plan my_plan;
-    
-    in = (fftw_complex*) fftw_malloc(sizeof(fftw_complex)*N);
-    out = (fftw_complex*) fftw_malloc(sizeof(fftw_complex)*N);
-    
-    // feed input
-    double x=0.0;
-    for (unsigned int i=0; i<N; i++) {
-        x = (double)i / (double)N;
-        in[i][0] = sin(100.0*x)*exp(-x/8.0);
-        in[i][1] = 0.0;
-//as35        if ((i%100)==0) std::cout << i << ": x=" << x << ", in=" << in[i][0] << std::endl;
-    }
-    
-    my_plan = fftw_plan_dft_1d(N, in, out, FFTW_FORWARD, FFTW_ESTIMATE);
-    
-    fftw_execute(my_plan);
-    
-    double sumRe = 0.0, sumIm = 0.0;
-    for (unsigned int i=0; i<N/2; i++) {
-//as35        if ((i % 10) == 0) std::cout << i << ": re=" << out[i][0] << ", im=" << out[i][1] << std::endl;
-        sumRe += out[i][0];
-        sumIm += out[i][1];
-    }
-    
-    std::cout << "sumRe=" << sumRe << std::endl;
-    std::cout << "sumIm=" << sumIm << std::endl;
-
-    fftw_destroy_plan(my_plan);
-    fftw_free(in);
-    fftw_free(out);
-    
-    return 0;
+void fftw3_test_syntax() {
+  std::cout << std::endl;
+  std::cout << "fftw3_test [N [offset]]" << std::endl;
+  std::cout << "  N: 2^N Fourier Power" << std::endl;
+  std::cout << "     default value if not given: N=13 (2^13 = 8192)" << std::endl;
+  std::cout << "  offset: allows to have a length != 2^N, namely 2^N + offset" << std::endl;
+  std::cout << "     default value of offset if not given is 0." << std::endl;
+  std::cout << std::endl;
+}
+
+int main(int argc, char *argv[]) {
+  unsigned int N=8192;
+  unsigned int offset=0;
+  
+  if (argc > 3) {
+    fftw3_test_syntax();
+    return 1;
+  }
+
+  int a=-1;
+  for (int i=1; i<argc; i++) {
+    int status = sscanf(argv[i], "%d", &a);
+    if (status != 1) {
+      fftw3_test_syntax();
+      return 2;
+    }
+    if (i==1) // N
+      N = (unsigned int)pow(2.0, a);
+    if (i==2) // offset
+      offset = (unsigned int)a;
+  }
+std::cout << "debug> N=" << N << ", offset=" << offset << std::endl;
+    
+  fftw_complex *in, *out;
+  fftw_plan my_plan;
+    
+  N += offset;
+  in = (fftw_complex*) fftw_malloc(sizeof(fftw_complex)*N);
+  out = (fftw_complex*) fftw_malloc(sizeof(fftw_complex)*N);
+    
+  // feed input
+  double x=0.0;
+  for (unsigned int i=0; i<N; i++) {
+    x = (double)i / (double)N;
+    in[i][0] = sin(100.0*x)*exp(-x/8.0);
+    in[i][1] = 0.0;
+//as35        if ((i%100)==0) std::cout << i << ": x=" << x << ", in=" << in[i][0] << std::endl;
+  }
+    
+  my_plan = fftw_plan_dft_1d(N, in, out, FFTW_FORWARD, FFTW_ESTIMATE);
+    
+  fftw_execute(my_plan);
+    
+  double sumRe = 0.0, sumIm = 0.0;
+  for (unsigned int i=0; i<N/2; i++) {
+//as35        if ((i % 10) == 0) std::cout << i << ": re=" << out[i][0] << ", im=" << out[i][1] << std::endl;
+    sumRe += out[i][0];
+    sumIm += out[i][1];
+  }
+    
+  std::cout << "sumRe=" << sumRe << std::endl;
+  std::cout << "sumIm=" << sumIm << std::endl;
+
+  fftw_destroy_plan(my_plan);
+  fftw_free(in);
+  fftw_free(out);
+    
+  return 0;
 }