fix tautological comparision

on platforms where `char` is implemented as `unsigned char`, addresses #378

src/synth/fluid_chan.h

@@ -65,8 +65,8 @@
 struct mononote
 {
     unsigned char next; /* next note */
-    char note; /* note */
+    unsigned char note; /* note */
-    char vel;  /* velocity */
+    unsigned char vel;  /* velocity */
 };
 
 /*
@@ -87,25 +87,25 @@ struct _fluid_channel_t
   /* monophonic list - legato detector */
   unsigned char i_first;          /**< First note index */
   unsigned char i_last;           /**< most recent note index since the most recent add */
-  char prev_note;                 /**< previous note of the most recent add/remove */
+  unsigned char prev_note;        /**< previous note of the most recent add/remove */
   unsigned char n_notes;          /**< actual number of notes in the list */
   struct mononote monolist[FLUID_CHANNEL_SIZE_MONOLIST];   /**< monophonic list */
   
-  char key_mono_sustained;         /**< previous sustained monophonic note */
+  unsigned char key_mono_sustained;         /**< previous sustained monophonic note */
-  char previous_cc_breath;		  /**< Previous Breath */
+  unsigned char previous_cc_breath;		  /**< Previous Breath */
   enum fluid_channel_legato_mode legatomode;       /**< legato mode */
   enum fluid_channel_portamento_mode portamentomode;   /**< portamento mode */
   /*- End of Poly/mono variables description */
   
-  char cc[128];                         /**< MIDI controller values */
+  unsigned char cc[128];                         /**< MIDI controller values from [0;127] */
-  char key_pressure[128];               /**< MIDI polyphonic key pressure */
+  unsigned char key_pressure[128];               /**< MIDI polyphonic key pressure from [0;127] */
   
   /* Drum channel flag, CHANNEL_TYPE_MELODIC, or CHANNEL_TYPE_DRUM. */
   enum fluid_midi_channel_type channel_type;
   enum fluid_interp interp_method;                    /**< Interpolation method (enum fluid_interp) */
 
-  char channel_pressure;                 /**< MIDI channel pressure */
+  unsigned char channel_pressure;                 /**< MIDI channel pressure from [0;127] */
-  char pitch_wheel_sensitivity;          /**< Current pitch wheel sensitivity */
+  unsigned char pitch_wheel_sensitivity;          /**< Current pitch wheel sensitivity */
   short pitch_bend;                      /**< Current pitch bend value */
   /* Sostenuto order id gives the order of SostenutoOn event.
    * This value is useful to known when the sostenuto pedal is depressed
@@ -231,7 +231,7 @@ int fluid_channel_get_interp_method(fluid_channel_t* chan);
                                              fluid_channel_legato(chan))
 
 /* Macros interface to monophonic list variables */
-#define INVALID_NOTE (-1)
+#define INVALID_NOTE (255)
 /* Returns true when a note is a valid note */
 #define fluid_channel_is_valid_note(n)    (n != INVALID_NOTE)
 /* Marks prev_note as invalid. */

src/synth/fluid_synth_monopoly.c

@@ -163,9 +163,9 @@
  * - In mono legato playing,default_fromkey must be valid.
  */
 static char fluid_synth_get_fromkey_portamento_legato(fluid_channel_t* chan, 
-								   char default_fromkey)
+								   int default_fromkey)
 {
-	char ptc =  fluid_channel_get_cc(chan, PORTAMENTO_CTRL);
+	unsigned char ptc = fluid_channel_get_cc(chan, PORTAMENTO_CTRL);
 	if(fluid_channel_is_valid_note(ptc))
 	{	/* CC PTC has been received */
 		fluid_channel_clear_portamento(chan);	/* clears the CC PTC receive */
@@ -178,7 +178,7 @@ static char fluid_synth_get_fromkey_portamento_legato(fluid_channel_t* chan,
 	}
 	else 
 	{	/* determines and returns fromkey portamento */
-		char fromkey_portamento = INVALID_NOTE;
+		unsigned char fromkey_portamento = INVALID_NOTE;
 		if(fluid_channel_portamento(chan))
 		{	/* Portamento when Portamento pedal is On */
 			/* 'fromkey portamento'is determined from the portamento mode