Allow sn76496 to output to mono.

src/burn/snd/sn76496.cpp

@@ -177,6 +177,131 @@ void SN76496Update(INT32 Num, INT16* pSoundBuf, INT32 Length)
 	}
 }
 
+void SN76496UpdateToBuffer(INT32 Num, INT16* pSoundBuf, INT32 Length)
+{
+#if defined FBA_DEBUG
+	if (!DebugSnd_SN76496Initted) bprintf(PRINT_ERROR, _T("SN76496Update called without init\n"));
+	if (Num > NumChips) bprintf(PRINT_ERROR, _T("SN76496Update called with invalid chip %x\n"), Num);
+#endif
+
+	INT32 i;
+	struct SN76496 *R = Chip0;
+	
+	if (Num >= MAX_SN76496_CHIPS) return;
+	
+	if (Num == 1) R = Chip1;
+	if (Num == 2) R = Chip2;
+	if (Num == 3) R = Chip3;
+	if (Num == 4) R = Chip4;
+	
+	/* If the volume is 0, increase the counter */
+	for (i = 0;i < 4;i++)
+	{
+		if (R->Volume[i] == 0)
+		{
+			/* note that I do count += length, NOT count = length + 1. You might think */
+			/* it's the same since the volume is 0, but doing the latter could cause */
+			/* interferencies when the program is rapidly modulating the volume. */
+			if (R->Count[i] <= Length*STEP) R->Count[i] += Length*STEP;
+		}
+	}
+
+	while (Length > 0)
+	{
+		INT32 Vol[4];
+		UINT32 Out;
+		INT32 Left;
+
+
+		/* vol[] keeps track of how long each square wave stays */
+		/* in the 1 position during the sample period. */
+		Vol[0] = Vol[1] = Vol[2] = Vol[3] = 0;
+
+		for (i = 0;i < 3;i++)
+		{
+			if (R->Output[i]) Vol[i] += R->Count[i];
+			R->Count[i] -= STEP;
+			/* Period[i] is the half period of the square wave. Here, in each */
+			/* loop I add Period[i] twice, so that at the end of the loop the */
+			/* square wave is in the same status (0 or 1) it was at the start. */
+			/* vol[i] is also incremented by Period[i], since the wave has been 1 */
+			/* exactly half of the time, regardless of the initial position. */
+			/* If we exit the loop in the middle, Output[i] has to be inverted */
+			/* and vol[i] incremented only if the exit status of the square */
+			/* wave is 1. */
+			while (R->Count[i] <= 0)
+			{
+				R->Count[i] += R->Period[i];
+				if (R->Count[i] > 0)
+				{
+					R->Output[i] ^= 1;
+					if (R->Output[i]) Vol[i] += R->Period[i];
+					break;
+				}
+				R->Count[i] += R->Period[i];
+				Vol[i] += R->Period[i];
+			}
+			if (R->Output[i]) Vol[i] -= R->Count[i];
+		}
+
+		Left = STEP;
+		do
+		{
+			INT32 NextEvent;
+
+
+			if (R->Count[3] < Left) NextEvent = R->Count[3];
+			else NextEvent = Left;
+
+			if (R->Output[3]) Vol[3] += R->Count[3];
+			R->Count[3] -= NextEvent;
+			if (R->Count[3] <= 0)
+			{
+		        if (R->NoiseMode == 1) /* White Noise Mode */
+		        {
+			        if (((R->RNG & R->WhitenoiseTaps) != R->WhitenoiseTaps) && ((R->RNG & R->WhitenoiseTaps) != 0)) /* crappy xor! */
+					{
+				        R->RNG >>= 1;
+				        R->RNG |= R->FeedbackMask;
+					}
+					else
+					{
+				        R->RNG >>= 1;
+					}
+					R->Output[3] = R->WhitenoiseInvert ? !(R->RNG & 1) : R->RNG & 1;
+				}
+				else /* Periodic noise mode */
+				{
+			        if (R->RNG & 1)
+					{
+				        R->RNG >>= 1;
+				        R->RNG |= R->FeedbackMask;
+					}
+					else
+					{
+				        R->RNG >>= 1;
+					}
+					R->Output[3] = R->RNG & 1;
+				}
+				R->Count[3] += R->Period[3];
+				if (R->Output[3]) Vol[3] += R->Period[3];
+			}
+			if (R->Output[3]) Vol[3] -= R->Count[3];
+
+			Left -= NextEvent;
+		} while (Left > 0);
+
+		Out = Vol[0] * R->Volume[0] + Vol[1] * R->Volume[1] +
+				Vol[2] * R->Volume[2] + Vol[3] * R->Volume[3];
+
+		if (Out > MAX_OUTPUT * STEP) Out = MAX_OUTPUT * STEP;
+
+		pSoundBuf[0] = BURN_SND_CLIP(((INT32)((Out / STEP) * R->nVolume)));
+		pSoundBuf++;
+		Length--;
+	}
+}
+
 void SN76496Write(INT32 Num, INT32 Data)
 {
 #if defined FBA_DEBUG

src/burn/snd/sn76496.h

@@ -1,4 +1,5 @@
 void SN76496Update(INT32 Num, INT16* pSoundBuf, INT32 Length);
+void SN76496UpdateToBuffer(INT32 Num, INT16* pSoundBuf, INT32 Length); // output mono
 void SN76496Write(INT32 Num, INT32 Data);
 void SN76489Init(INT32 Num, INT32 Clock, INT32 SignalAdd);
 void SN76489AInit(INT32 Num, INT32 Clock, INT32 SignalAdd);