added sound length computation

src/vm/lua_bridge.cpp

@@ -633,7 +633,7 @@ namespace sound
     sfx::sound_index_t index = lua_tonumber(L, 1);
     sfx::channel_index_t channel = lua_to_or_default(L, number, 2, -1);
     int32_t start = lua_to_or_default(L, number, 3, 0);
-    int32_t end = lua_to_or_default(L, number, 3, 31); //TODO: actual length
+    int32_t end = lua_to_or_default(L, number, 3, machine.memory().sound(index)->length());
 
     machine.sound().play(index, channel, start, end);
 

src/vm/sound.h

@@ -81,6 +81,17 @@ namespace retro8
       uint8_t speed; // 1 note = 1/128 sec * speed
       uint8_t loopStart;
       uint8_t loopEnd;
+
+      int32_t length() const
+      {        
+        for (int32_t l = samples.size() - 1; l > 0; --l)
+        {
+          if (samples[l].volume() > 0)
+            return l;
+        }
+
+        return 1;
+      }
     };
 
     struct Music