Fix inf/nan problems for fft bands with mag = 0.0.

Signed-off-by: Stefan Westerfeld <stefan@space.twc.de>

src/audiowmark.cc

@@ -346,6 +346,7 @@ mark_bit_linear (int f, const vector<complex<float>>& fft_out, vector<complex<fl
   vector<int> down;
   get_up_down (f, up, down, random_stream);
   const double  data_bit_sign = data_bit > 0 ? 1 : -1;
+  const float   min_mag = 1e-7;   // avoid computing pow (0.0, -water_delta) which would be inf
   for (auto u : up)
     {
       /*
@@ -353,10 +354,14 @@ mark_bit_linear (int f, const vector<complex<float>>& fft_out, vector<complex<fl
        *
        * this actually increases the amount of energy because mag is less than 1.0
        */
-      const float mag_factor = pow (abs (fft_out[u]), -Params::water_delta * data_bit_sign);
+      const float mag = abs (fft_out[u]);
+      if (mag > min_mag)
+        {
+          const float mag_factor = pow (mag, -Params::water_delta * data_bit_sign);
 
           fft_delta_spect[u] = fft_out[u] * (mag_factor - 1);
         }
+    }
   for (auto d : down)
     {
       /*
@@ -364,10 +369,14 @@ mark_bit_linear (int f, const vector<complex<float>>& fft_out, vector<complex<fl
        *
        * this actually decreases the amount of energy because mag is less than 1.0
        */
-      const float mag_factor = pow (abs (fft_out[d]), Params::water_delta * data_bit_sign);
+      const float mag = abs (fft_out[d]);
+      if (mag > min_mag)
+        {
+          const float mag_factor = pow (mag, Params::water_delta * data_bit_sign);
 
           fft_delta_spect[d] = fft_out[d] * (mag_factor - 1);
         }
+    }
 }
 
 size_t
@@ -412,6 +421,7 @@ mark_data (const WavData& wav_data, int start_frame, const vector<vector<complex
   assert (bitvec.size() == mark_data_frame_count() / Params::frames_per_bit);
 
   const int   frame_count = mark_data_frame_count();
+  const float min_mag = 1e-7;   // avoid computing pow (0.0, -water_delta) which would be inf
 
   if (Params::mix)
     {
@@ -431,13 +441,20 @@ mark_data (const WavData& wav_data, int start_frame, const vector<vector<complex
                   const int u = mix_entries[b].up;
                   const int index = (start_frame + mix_entries[b].frame) * wav_data.n_channels() + ch;
                   {
-                    const float mag_factor = pow (abs (fft_out[index][u]), -Params::water_delta * data_bit_sign);
+                    const float mag = abs (fft_out[index][u]);
+                    if (mag > min_mag)
+                      {
+                        const float mag_factor = pow (mag, -Params::water_delta * data_bit_sign);
 
                         fft_delta_spect[index][u] = fft_out[index][u] * (mag_factor - 1);
                       }
+                  }
                   const int d = mix_entries[b].down;
                   {
-                    const float mag_factor = pow (abs (fft_out[index][d]), Params::water_delta * data_bit_sign);
+                    const float mag = abs (fft_out[index][d]);
+                    if (mag > min_mag)
+                      {
+                        const float mag_factor = pow (mag, Params::water_delta * data_bit_sign);
 
                         fft_delta_spect[index][d] = fft_out[index][d] * (mag_factor - 1);
                       }
@@ -445,6 +462,7 @@ mark_data (const WavData& wav_data, int start_frame, const vector<vector<complex
                 }
             }
         }
+    }
   else
     {
       for (int f = 0; f < frame_count; f++)