pce: reduce per-iteration conditional statements in psg

This also significantly increases performance
ares-emulator · Jan 31, 2025 · 6cc9f5a · 6cc9f5a
1 parent 69c2071
commit 6cc9f5a
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Showing 5 changed files with 31 additions and 33 deletions.
diff --git a/ares/pce/psg/channel.cpp b/ares/pce/psg/channel.cpp
@@ -3,27 +3,22 @@ auto PSG::Channel::power(u32 id) -> void {
   io = {};
 }
 
-auto PSG::Channel::run() -> void {
-  if(!io.enable) return sample(0);
+template<int index, int step> auto PSG::Channel::run() -> n5 {
+  for(u32 n : range(step)) {
+    if(!io.direct && --io.wavePeriod == 0) {
+      io.wavePeriod = io.waveFrequency;
+      io.waveOffset++;
+      io.waveSample = io.waveBuffer[io.waveOffset];
+    }
 
-  if(!io.direct && --io.wavePeriod == 0) {
-    io.wavePeriod = io.waveFrequency;
-    io.waveOffset++;
-    io.waveSample = io.waveBuffer[io.waveOffset];
+    //Only channels 4-5 support noise
+    if(index >= 4 && io.noiseEnable) {
+      if(--io.noisePeriod == 0) {
+        io.noisePeriod = ~io.noiseFrequency << 7;
+        io.noiseSample = nall::random() & 1 ? ~0 : 0;
+      }
+    }
   }
 
-  if(!io.noiseEnable) {
-    return sample(io.waveSample);
-  }
-
-  if(--io.noisePeriod == 0) {
-    io.noisePeriod = ~io.noiseFrequency << 7;
-    io.noiseSample = nall::random() & 1 ? ~0 : 0;
-  }
-
-  return sample(io.noiseSample);
-}
-
-auto PSG::Channel::sample(n5 sample) -> void {
-  io.output = sample;
+  return index >= 4 && io.noiseEnable ? io.noiseSample : io.waveSample;
 }
diff --git a/ares/pce/psg/psg.cpp b/ares/pce/psg/psg.cpp
@@ -32,21 +32,21 @@ auto PSG::main() -> void {
   i16 outputRight;
 
   #if defined(PROFILE_ACCURACY)
-  frame(outputLeft, outputRight);
+  frame<1>(outputLeft, outputRight);
   stream->frame(sclamp<16>(outputLeft) / 32768.0, sclamp<16>(outputRight) / 32768.0);
   step(1);
   #endif
 
   #if defined(PROFILE_PERFORMANCE)
   //3.57MHz stereo audio through a 6th-order biquad IIR filter is very demanding.
   //decimate the audio to ~56KHz, which is still well above the range of human hearing.
-  for(u32 n : range(64)) frame(outputLeft, outputRight);
+  frame<64>(outputLeft, outputRight);
   stream->frame(sclamp<16>(outputLeft) / 32768.0, sclamp<16>(outputRight) / 32768.0);
   step(64);
   #endif
 }
 
-auto PSG::frame(i16& outputLeft, i16& outputRight) -> void {
+template<int step> auto PSG::frame(i16& outputLeft, i16& outputRight) -> void {
   static const n5 volumeScale[16] = {
     0x00, 0x03, 0x05, 0x07, 0x09, 0x0b, 0x0d, 0x0f,
     0x10, 0x13, 0x15, 0x17, 0x19, 0x1b, 0x1d, 0x1f,
@@ -58,6 +58,14 @@ auto PSG::frame(i16& outputLeft, i16& outputRight) -> void {
   n5 lmal = volumeScale[io.volumeLeft];
   n5 rmal = volumeScale[io.volumeRight];
 
+  n5 output[6];
+  if(channel[0].io.enable) output[0] = channel[0].run<0, step>();
+  if(channel[1].io.enable) output[1] = channel[1].run<1, step>();
+  if(channel[2].io.enable) output[2] = channel[2].run<2, step>();
+  if(channel[3].io.enable) output[3] = channel[3].run<3, step>();
+  if(channel[4].io.enable) output[4] = channel[4].run<4, step>();
+  if(channel[5].io.enable) output[5] = channel[5].run<5, step>();
+
   for(u32 C : range(6)) {
     n5  al = channel[C].io.volume;
     n5 lal = volumeScale[channel[C].io.volumeLeft];
@@ -66,12 +74,11 @@ auto PSG::frame(i16& outputLeft, i16& outputRight) -> void {
     n5 volumeLeft  = min(0x1f, (0x1f - lmal) + (0x1f - lal) + (0x1f - al));
     n5 volumeRight = min(0x1f, (0x1f - rmal) + (0x1f - ral) + (0x1f - al));
 
-    channel[C].run();
     if(C == 1 && io.lfoEnable) {
       //todo: frequency modulation of channel 0 using channel 1's output
     } else {
-      outputLeft  += channel[C].io.output * volumeScalar[volumeLeft];
-      outputRight += channel[C].io.output * volumeScalar[volumeRight];
+      outputLeft  += output[C] * volumeScalar[volumeLeft];
+      outputRight += output[C] * volumeScalar[volumeRight];
     }
   }
 }

diff --git a/ares/pce/psg/psg.hpp b/ares/pce/psg/psg.hpp
@@ -9,7 +9,7 @@ struct PSG : Thread {
   auto unload() -> void;
 
   auto main() -> void;
-  auto frame(i16&, i16&) -> void;
+  template<int step> auto frame(i16&, i16&) -> void;
   auto step(u32 clocks) -> void;
 
   auto power() -> void;
@@ -33,8 +33,7 @@ struct PSG : Thread {
   struct Channel {
     //channel.cpp
     auto power(u32 id) -> void;
-    auto run() -> void;
-    auto sample(n5 sample) -> void;
+    template<int channel, int step> auto run() -> n5;
 
     //io.cpp
     auto write(n4 address, n8 data) -> void;
@@ -55,8 +54,6 @@ struct PSG : Thread {
       n5  waveOffset;
       n12 noisePeriod;
       n5  noiseSample;
-
-      n5  output;
     } io;
 
     u32 id;

diff --git a/ares/pce/psg/serialization.cpp b/ares/pce/psg/serialization.cpp
@@ -23,6 +23,5 @@ auto PSG::serialize(serializer& s) -> void {
     s(c.io.waveOffset);
     s(c.io.noisePeriod);
     s(c.io.noiseSample);
-    s(c.io.output);
   }
 }
diff --git a/ares/pce/system/serialization.cpp b/ares/pce/system/serialization.cpp
@@ -1,4 +1,4 @@
-static const string SerializerVersion = "v132";
+static const string SerializerVersion = "v133";
 
 auto System::serialize(bool synchronize) -> serializer {
   if(synchronize) scheduler.enter(Scheduler::Mode::Synchronize);