From 64c526ede27cb9cafc7a9f7308b42a4ab80f9464 Mon Sep 17 00:00:00 2001
From: Ziemas <ziemas@ziemas.se>
Date: Wed, 17 Feb 2021 23:32:28 +0100
Subject: [PATCH] SPU2: Optimize reverb upsampling

Skip the 0 coefs here as well.
---
 pcsx2/SPU2/Reverb.cpp | 24 ++++++++++++++++--------
 pcsx2/SPU2/defs.h     |  2 +-
 2 files changed, 17 insertions(+), 9 deletions(-)

diff --git a/pcsx2/SPU2/Reverb.cpp b/pcsx2/SPU2/Reverb.cpp
index 7181d61dd9..d93cf0914a 100644
--- a/pcsx2/SPU2/Reverb.cpp
+++ b/pcsx2/SPU2/Reverb.cpp
@@ -112,17 +112,26 @@ s32 __forceinline V_Core::ReverbDownsample(bool right)
 }
 
 
-StereoOut32 __forceinline V_Core::ReverbUpsample()
+StereoOut32 __forceinline V_Core::ReverbUpsample(bool phase)
 {
 	s32 ls = 0, rs = 0;
 
-	for (u32 i = 0; i < NUM_TAPS; i++)
+	if (phase)
 	{
-		ls += RevbUpBuf[0][((RevbSampleBufPos - NUM_TAPS) + i) & 63] * filter_coefs[i];
+		ls += RevbUpBuf[0][(((RevbSampleBufPos - NUM_TAPS) >> 1) + 9) & 63] * filter_coefs[19];
+		rs += RevbUpBuf[1][(((RevbSampleBufPos - NUM_TAPS) >> 1) + 9) & 63] * filter_coefs[19];
 	}
-	for (u32 i = 0; i < NUM_TAPS; i++)
+	else
 	{
-		rs += RevbUpBuf[1][((RevbSampleBufPos - NUM_TAPS) + i) & 63] * filter_coefs[i];
+
+		for (u32 i = 0; i < (NUM_TAPS >> 1) + 1; i++)
+		{
+			ls += RevbUpBuf[0][(((RevbSampleBufPos - NUM_TAPS) >> 1) + i) & 63] * filter_coefs[i * 2];
+		}
+		for (u32 i = 0; i < (NUM_TAPS >> 1) + 1; i++)
+		{
+			rs += RevbUpBuf[1][(((RevbSampleBufPos - NUM_TAPS) >> 1) + i) & 63] * filter_coefs[i * 2];
+		}
 	}
 
 	ls >>= 14;
@@ -223,10 +232,9 @@ StereoOut32 V_Core::DoReverb(const StereoOut32& Input)
 		_spu2mem[apf2_dst] = clamp_mix(apf2);
 	}
 
-	RevbUpBuf[0][RevbSampleBufPos & 63] = R ? 0 : clamp_mix(out);
-	RevbUpBuf[1][RevbSampleBufPos & 63] = R ? clamp_mix(out) : 0;
+	RevbUpBuf[R][(RevbSampleBufPos >> 1) & 63] = clamp_mix(out);
 
 	RevbSampleBufPos++;
 
-	return ReverbUpsample();
+	return ReverbUpsample(RevbSampleBufPos & 1);
 }
diff --git a/pcsx2/SPU2/defs.h b/pcsx2/SPU2/defs.h
index dfdc19b993..4fd5a161ac 100644
--- a/pcsx2/SPU2/defs.h
+++ b/pcsx2/SPU2/defs.h
@@ -497,7 +497,7 @@ struct V_Core
 	s32 RevbGetIndexer(s32 offset);
 
 	s32 ReverbDownsample(bool right);
-	StereoOut32 ReverbUpsample();
+	StereoOut32 ReverbUpsample(bool phase);
 
 	StereoOut32 ReadInput();
 	StereoOut32 ReadInput_HiFi();