Always write/read up/down pairs in --mix.

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

src/audiowmark.cc

@@ -22,7 +22,7 @@ namespace Params
   static size_t frame_size   = 1024;
   static int frames_per_bit  = 4;
   static int block           = 1;
-  static int bands_per_frame = 30;
+  static size_t bands_per_frame = 30;
   static int max_band        = 100;
   static int min_band        = 20;
   static double water_delta  = 0.015; // strength of the watermark
@@ -463,22 +463,21 @@ add_watermark (const string& infile, const string& outfile, const string& bits)
     {
       struct MixEntry {
         int  frame;
-        int  band;
+        int  up;
+        int  down;
       };
-      vector<MixEntry> up_entries, down_entries;
+      vector<MixEntry> mix_entries;
       for (int f = 0; f < Params::block * Params::frames_per_bit; f++)
         {
           vector<int> up;
           vector<int> down;
           get_up_down (f, up, down);
 
-          for (auto u : up)
-            up_entries.push_back ({ f, u });
-          for (auto d : down)
-            down_entries.push_back ({ f, d });
+          assert (up.size() == down.size());
+          for (size_t i = 0; i < up.size(); i++)
+            mix_entries.push_back ({ f, up[i], down[i] });
         }
-      gen_shuffle2 (up_entries, /* seed */ 0);
-      gen_shuffle2 (down_entries, /* seed */ 1);
+      gen_shuffle2 (mix_entries, /* seed */ 0);
 
       vector<vector<complex<float>>> fft_out;
       vector<vector<complex<float>>> fft_delta_spect;
@@ -520,17 +519,17 @@ add_watermark (const string& infile, const string& outfile, const string& bits)
                   const int data_bit = bitvec[(f / Params::frames_per_bit) % bitvec.size()];
                   const double  data_bit_sign = data_bit > 0 ? 1 : -1;
 
-                  const int u = up_entries[b].band;
+                  const int u = mix_entries[b].up;
                   {
-                    const float mag_factor = pow (abs (fft_out[up_entries[b].frame * wav_data.n_channels() + ch][u]), -Params::water_delta * data_bit_sign);
+                    const float mag_factor = pow (abs (fft_out[mix_entries[b].frame * wav_data.n_channels() + ch][u]), -Params::water_delta * data_bit_sign);
 
-                    fft_delta_spect[up_entries[b].frame * wav_data.n_channels() + ch][u] = fft_out[up_entries[b].frame * wav_data.n_channels() + ch][u] * (mag_factor - 1);
+                    fft_delta_spect[mix_entries[b].frame * wav_data.n_channels() + ch][u] = fft_out[mix_entries[b].frame * wav_data.n_channels() + ch][u] * (mag_factor - 1);
                   }
-                  const int d = down_entries[b].band;
+                  const int d = mix_entries[b].down;
                   {
-                    const float mag_factor = pow (abs (fft_out[down_entries[b].frame * wav_data.n_channels() + ch][d]), Params::water_delta * data_bit_sign);
+                    const float mag_factor = pow (abs (fft_out[mix_entries[b].frame * wav_data.n_channels() + ch][d]), Params::water_delta * data_bit_sign);
 
-                    fft_delta_spect[down_entries[b].frame * wav_data.n_channels() + ch][d] = fft_out[down_entries[b].frame * wav_data.n_channels() + ch][d] * (mag_factor - 1);
+                    fft_delta_spect[mix_entries[b].frame * wav_data.n_channels() + ch][d] = fft_out[mix_entries[b].frame * wav_data.n_channels() + ch][d] * (mag_factor - 1);
                   }
                 }
             }
@@ -629,22 +628,21 @@ get_watermark (const string& infile, const string& orig_pattern)
     {
       struct MixEntry {
         int  frame;
-        int  band;
+        int  up;
+        int  down;
       };
-      vector<MixEntry> up_entries, down_entries;
+      vector<MixEntry> mix_entries;
       for (int f = 0; f < Params::block * Params::frames_per_bit; f++)
         {
           vector<int> up;
           vector<int> down;
           get_up_down (f, up, down);
 
-          for (auto u : up)
-            up_entries.push_back ({ f, u });
-          for (auto d : down)
-            down_entries.push_back ({ f, d });
+          assert (up.size() == down.size());
+          for (size_t i = 0; i < up.size(); i++)
+            mix_entries.push_back ({ f, up[i], down[i] });
         }
-      gen_shuffle2 (up_entries, /* seed */ 0);
-      gen_shuffle2 (down_entries, /* seed */ 1);
+      gen_shuffle2 (mix_entries, /* seed */ 0);
 
       vector<vector<complex<float>>> fft_out;
       for (int f = 0; f < Params::block * Params::frames_per_bit; f++)
@@ -683,13 +681,13 @@ get_watermark (const string& infile, const string& orig_pattern)
                   int b = f * Params::bands_per_frame + frame_b;
                   const double min_db = -96;
 
-                  const int u = up_entries[b].band;
+                  const int u = mix_entries[b].up;
                   {
-                    umag += db_from_factor (abs (fft_out[up_entries[b].frame * wav_data.n_channels() + ch][u]), min_db);
+                    umag += db_from_factor (abs (fft_out[mix_entries[b].frame * wav_data.n_channels() + ch][u]), min_db);
                   }
-                  const int d = down_entries[b].band;
+                  const int d = mix_entries[b].down;
                   {
-                    dmag += db_from_factor (abs (fft_out[down_entries[b].frame * wav_data.n_channels() + ch][d]), min_db);
+                    dmag += db_from_factor (abs (fft_out[mix_entries[b].frame * wav_data.n_channels() + ch][d]), min_db);
                   }
                 }
             }