From e8130caa5211389c263ba8cec0a6ef9a89446d17 Mon Sep 17 00:00:00 2001
From: tildearrow <me@tildearrow.org>
Date: Tue, 11 Jul 2023 17:21:51 -0500
Subject: [PATCH] C64: fix dSID multi-chip

---
 src/engine/platform/c64.cpp            | 18 ++++++++++++++++++
 src/engine/platform/c64.h              |  1 +
 src/engine/platform/sound/c64_d/dsid.c | 19 +++++++++++--------
 src/engine/platform/sound/c64_d/dsid.h |  2 ++
 4 files changed, 32 insertions(+), 8 deletions(-)

diff --git a/src/engine/platform/c64.cpp b/src/engine/platform/c64.cpp
index b41a52d5..028bb94d 100644
--- a/src/engine/platform/c64.cpp
+++ b/src/engine/platform/c64.cpp
@@ -613,6 +613,24 @@ void DivPlatformC64::setFlags(const DivConfig& flags) {
   keyPriority=flags.getBool("keyPriority",true);
   testAD=((flags.getInt("testAttack",0)&15)<<4)|(flags.getInt("testDecay",0)&15);
   testSR=((flags.getInt("testSustain",0)&15)<<4)|(flags.getInt("testRelease",0)&15);
+
+  // init fake filter table
+  // taken from dSID
+  double cutRatio=-2.0*3.14*(sidIs6581?(((double)oscBuf[0]->rate/44100.0)*(20000.0/256.0)):(12500.0/256.0))/(double)oscBuf[0]->rate;
+
+  for (int i=0; i<2048; i++) {
+    double c=(double)i/8.0+0.2;
+    if (sidIs6581) {
+      if (c<24) {
+        c=2.0*sin(771.78/(double)oscBuf[0]->rate);
+      } else {
+        c=(44100.0/(double)oscBuf[0]->rate)-1.263*(44100.0/(double)oscBuf[0]->rate)*exp(c*cutRatio);
+      }
+    } else {
+      c=1-exp(c*cutRatio);
+    }
+    fakeCutTable[i]=c;
+  }
 }
 
 int DivPlatformC64::init(DivEngine* p, int channels, int sugRate, const DivConfig& flags) {
diff --git a/src/engine/platform/c64.h b/src/engine/platform/c64.h
index 26b39c80..44db167d 100644
--- a/src/engine/platform/c64.h
+++ b/src/engine/platform/c64.h
@@ -56,6 +56,7 @@ class DivPlatformC64: public DivDispatch {
   Channel chan[3];
   DivDispatchOscBuffer* oscBuf[3];
   bool isMuted[3];
+  float fakeCutTable[2048];
   struct QueuedWrite {
       unsigned char addr;
       unsigned char val;
diff --git a/src/engine/platform/sound/c64_d/dsid.c b/src/engine/platform/sound/c64_d/dsid.c
index d01dc7ad..2ff2dacf 100644
--- a/src/engine/platform/sound/c64_d/dsid.c
+++ b/src/engine/platform/sound/c64_d/dsid.c
@@ -115,11 +115,17 @@ void dSID_init(struct SID_chip* sid, double clockRate, double samplingRate, int
     double prd0 = sid->g.ckr > 9 ? sid->g.ckr : 9;
     sid->g.Aprd[0] = prd0;
     sid->g.Astp[0] = ceil(prd0 / 9);
+
+    for (int i=0; i<3; i++) {
+      sid->fakeplp[i]=0;
+      sid->fakepbp[i]=0;
+    }
 }
 
 double dSID_render(struct SID_chip* sid) {
     double flin = 0, output = 0;
     double wfout = 0;
+    double step = 0;
     for (int chn = 0; chn < 3; chn++) {
         struct SIDVOICE *voic = &((struct SIDMEM *) (sid->M))->v[chn];
         double pgt = (sid->SIDct->ch[chn].Ast & GAT);
@@ -142,7 +148,6 @@ double dSID_render(struct SID_chip* sid) {
         if (sid->SIDct->ch[chn].rcnt >= 0x8000)
             sid->SIDct->ch[chn].rcnt -= 0x8000;
 
-        static double step;
         double prd;
 
         if (sid->SIDct->ch[chn].Ast & ATK) {
@@ -291,8 +296,6 @@ double dSID_render(struct SID_chip* sid) {
                 // mostly copypasted from below
                 double fakeflin = chnout;
                 double fakeflout = 0;
-                static double fakeplp[3] = {0};
-                static double fakepbp[3] = {0};
                 double ctf = sid->g.ctf_table[((sid->M[0x15]&7)|(sid->M[0x16]<<3))&0x7ff];
                 double reso;
                 if (sid->g.model == 8580) {
@@ -300,15 +303,15 @@ double dSID_render(struct SID_chip* sid) {
                 } else {
                     reso = (sid->M[0x17] > 0x5F) ? 8.0 / (double) (sid->M[0x17] >> 4) : 1.41;
                 }
-                double tmp = fakeflin + fakepbp[chn] * reso + fakeplp[chn];
+                double tmp = fakeflin + sid->fakepbp[chn] * reso + sid->fakeplp[chn];
                 if (sid->M[0x18] & HP)
                     fakeflout -= tmp;
-                tmp = fakepbp[chn] - tmp * ctf;
-                fakepbp[chn] = tmp;
+                tmp = sid->fakepbp[chn] - tmp * ctf;
+                sid->fakepbp[chn] = tmp;
                 if (sid->M[0x18] & BP)
                     fakeflout -= tmp;
-                tmp = fakeplp[chn] + tmp * ctf;
-                fakeplp[chn] = tmp;
+                tmp = sid->fakeplp[chn] + tmp * ctf;
+                sid->fakeplp[chn] = tmp;
                 if (sid->M[0x18] & LP)
                     fakeflout += tmp;
 
diff --git a/src/engine/platform/sound/c64_d/dsid.h b/src/engine/platform/sound/c64_d/dsid.h
index b02d1870..b17a51f5 100644
--- a/src/engine/platform/sound/c64_d/dsid.h
+++ b/src/engine/platform/sound/c64_d/dsid.h
@@ -81,6 +81,8 @@ struct SID_chip {
     uint8_t M[MemLen];
     int16_t lastOut[3];
     int mute_mask;
+    double fakeplp[3];
+    double fakepbp[3];
 };
 
 double dSID_render(struct SID_chip* sid);