Optimize synth code by pre-computing the volume scaling for each note.

Scaling is now calculated once per MIDI event at the most, instead of
once per sample. Increase voice ramping speed, increase number of
active voices a little.


git-svn-id: svn://svn.rockbox.org/rockbox/trunk@9870 a1c6a512-1295-4272-9138-f99709370657

apps/plugins/midi/midiutil.c

@@ -127,6 +127,7 @@ struct SynthObject
     int note, vol, ch, isUsed;
     int curRate, curOffset, targetOffset;
     int curPoint;
+    signed short int volscale;
 };
 
 struct SynthObject voices[MAX_VOICES] IBSS_ATTR;