GBA Audio: Claw back some performance

include/mgba/internal/gba/audio.h

@@ -16,6 +16,7 @@ CXX_GUARD_START
 #include <mgba-util/circle-buffer.h>
 
 #define GBA_AUDIO_FIFO_SIZE 8
+#define GBA_MAX_SAMPLES 16
 
 #define MP2K_MAGIC 0x68736D53
 #define MP2K_MAX_SOUND_CHANNELS 12
@@ -34,7 +35,7 @@ struct GBAAudioFIFO {
 	uint32_t internalSample;
 	int internalRemaining;
 	int dmaSource;
-	int8_t samples[8];
+	int8_t samples[GBA_MAX_SAMPLES];
 };
 
 DECL_BITFIELD(GBARegisterSOUNDCNT_HI, uint16_t);

include/mgba/internal/gba/serialize.h

@@ -225,8 +225,8 @@ mLOG_DECLARE_CATEGORY(GBA_STATE);
  * 0x00324 - 0x00327: Interruptable BIOS stall cycles
  * 0x00328 - 0x00367: Matrix memory mapping table
  * 0x00368 - 0x0036F: Reserved (leave zero)
- * 0x00370 - 0x00377: Audio FIFO A samples
- * 0x00378 - 0x0037F: Audio FIFO B samples
+ * 0x00370 - 0x0037F: Audio FIFO A samples
+ * 0x00380 - 0x0038F: Audio FIFO B samples
  * 0x00380 - 0x003FF: Reserved (leave zero)
  * 0x00400 - 0x007FF: I/O memory
  * 0x00800 - 0x00BFF: Palette
@@ -387,11 +387,11 @@ struct GBASerializedState {
     uint32_t reservedMatrix[2];
 
     struct {
-        int8_t chA[8];
-        int8_t chB[8];
+        int8_t chA[16];
+        int8_t chB[16];
     } samples;
 
-	uint32_t reserved[32];
+	uint32_t reserved[28];
 
 	uint16_t io[SIZE_IO >> 1];
 	uint16_t pram[SIZE_PALETTE_RAM >> 1];

src/gb/audio.c

@@ -566,29 +566,28 @@ void GBAudioRun(struct GBAudio* audio, int32_t timestamp, int channels) {
 		cycles <<= audio->ch4.frequency;
 		cycles *= 8 * audio->timingFactor;
 
-		int32_t last = 0;
 		int32_t diff = timestamp - audio->ch4.lastEvent;
-		int samples = 0;
-		int positiveSamples = 0;
-		int lsb;
-		int coeff = 0x60;
-		if (!audio->ch4.power) {
-			coeff <<= 8;
-		}
-		for (; last + cycles <= diff; last += cycles) {
-			lsb = audio->ch4.lfsr & 1;
-			audio->ch4.lfsr >>= 1;
-			audio->ch4.lfsr ^= lsb * coeff;
-			++samples;
-			positiveSamples += lsb;
-		}
-		if (samples) {
+		if (diff >= cycles) {
+			int32_t last;
+			int samples = 0;
+			int positiveSamples = 0;
+			int lsb;
+			int coeff = 0x60;
+			if (!audio->ch4.power) {
+				coeff <<= 8;
+			}
+			for (last = 0; last + cycles <= diff; last += cycles) {
+				lsb = audio->ch4.lfsr & 1;
+				audio->ch4.lfsr >>= 1;
+				audio->ch4.lfsr ^= lsb * coeff;
+				++samples;
+				positiveSamples += lsb;
+			}
 			audio->ch4.sample = lsb * audio->ch4.envelope.currentVolume;
 			audio->ch4.nSamples += samples;
 			audio->ch4.samples += positiveSamples * audio->ch4.envelope.currentVolume;
+			audio->ch4.lastEvent += last;
 		}
-
-		audio->ch4.lastEvent += last;
 	}
 }
 

src/gba/audio.c

@@ -25,7 +25,7 @@ mLOG_DEFINE_CATEGORY(GBA_AUDIO, "GBA Audio", "gba.audio");
 const unsigned GBA_AUDIO_SAMPLES = 2048;
 const int GBA_AUDIO_VOLUME_MAX = 0x100;
 
-static const int SAMPLE_INTERVAL = GBA_ARM7TDMI_FREQUENCY / 0x8000;
+static const int SAMPLE_INTERVAL = GBA_ARM7TDMI_FREQUENCY / 0x4000;
 static const int CLOCKS_PER_FRAME = 0x800;
 
 static int _applyBias(struct GBAAudio* audio, int sample);
@@ -305,14 +305,11 @@ void GBAAudioSampleFIFO(struct GBAAudio* audio, int fifoId, int32_t cycles) {
 		}
 	}
 	int32_t until = mTimingUntil(&audio->p->timing, &audio->sampleEvent) - 1;
-	int bits = 1 << GBARegisterSOUNDBIASGetResolution(audio->soundbias);
+	int bits = 2 << GBARegisterSOUNDBIASGetResolution(audio->soundbias);
 	until += 1 << (9 - GBARegisterSOUNDBIASGetResolution(audio->soundbias));
 	until >>= 9 - GBARegisterSOUNDBIASGetResolution(audio->soundbias);
 	int i;
 	for (i = bits - until; i < bits; ++i) {
-		if (i < 0 || i >= bits) {
-			abort();
-		}
 		channel->samples[i] = channel->internalSample;
 	}
 	if (channel->internalRemaining) {
@@ -333,8 +330,8 @@ static int _applyBias(struct GBAAudio* audio, int sample) {
 
 static void _sample(struct mTiming* timing, void* user, uint32_t cyclesLate) {
 	struct GBAAudio* audio = user;
-	int16_t samplesLeft[8];
-	int16_t samplesRight[8];
+	int16_t samplesLeft[GBA_MAX_SAMPLES];
+	int16_t samplesRight[GBA_MAX_SAMPLES];
 	int32_t timestamp = mTimingCurrentTime(&audio->p->timing) - cyclesLate - SAMPLE_INTERVAL;
 	int sample;
 	for (sample = 0; sample * audio->sampleInterval < (int32_t) SAMPLE_INTERVAL; ++sample) {