potentially breaking change: better freq formula

now using a 4096-entry-long table for calculating final period/frequency
see issue #303

src/engine/engine.cpp

@@ -832,9 +832,17 @@ double DivEngine::calcBaseFreq(double clock, double divider, int note, bool peri
 
 int DivEngine::calcFreq(int base, int pitch, bool period, int octave) {
   if (song.linearPitch) {
+    pitch+=2048;
+    if (pitch<0) pitch=0;
+    if (pitch>4095) pitch=4095;
+    return period?
+            (base*reversePitchTable[pitch])>>10:
+            (base*pitchTable[pitch])>>10;
+    /*
     return period?
             base*pow(2,-(double)pitch/(12.0*128.0))/(98.0+globalPitch*6.0)*98.0:
             (base*pow(2,(double)pitch/(12.0*128.0))*(98+globalPitch*6))/98;
+    */
   }
   return period?
            base-pitch:
@@ -2850,6 +2858,10 @@ bool DivEngine::init() {
   for (int i=0; i<64; i++) {
     vibTable[i]=127*sin(((double)i/64.0)*(2*M_PI));
   }
+  for (int i=0; i<4096; i++) {
+    reversePitchTable[i]=round(1024.0*pow(2.0,(2048.0-(double)i)/(12.0*128.0)));
+    pitchTable[i]=round(1024.0*pow(2.0,((double)i-2048.0)/(12.0*128.0)));
+  }
 
   for (int i=0; i<DIV_MAX_CHANS; i++) {
     isMuted[i]=0;

src/engine/engine.h

@@ -227,6 +227,8 @@ class DivEngine {
   } sPreview;
 
   short vibTable[64];
+  int reversePitchTable[4096];
+  int pitchTable[4096];
 
   blip_buffer_t* samp_bb;
   size_t samp_bbInLen;

src/engine/platform/vic20.cpp

@@ -22,10 +22,12 @@
 #include <math.h>
 
 #define rWrite(a,v) {regPool[(a)]=(v)&0xff; vic_sound_machine_store(vic,a,(v)&0xff);}
-
-#define CHIP_DIVIDER 32
 #define SAMP_DIVIDER 4
 
+const int chipDividers[4]={
+  128, 64, 32, 64
+};
+
 const char* regCheatSheetVIC[]={
   "CH1_Pitch", "0A",
   "CH2_Pitch", "0B",
@@ -93,6 +95,7 @@ void DivPlatformVIC20::writeOutVol(int ch) {
 
 void DivPlatformVIC20::tick() {
   for (int i=0; i<4; i++) {
+    int CHIP_DIVIDER=chipDividers[i];
     chan[i].std.next();
     if (chan[i].std.hadVol) {
       int env=chan[i].std.vol;
@@ -121,10 +124,9 @@ void DivPlatformVIC20::tick() {
     }
     if (chan[i].freqChanged || chan[i].keyOn || chan[i].keyOff) {
       chan[i].freq=parent->calcFreq(chan[i].baseFreq,chan[i].pitch,true);
-      if (i<3) chan[i].freq>>=(2-i);
-      else chan[i].freq>>=1;
+      printf("%d freq: %d\n",i,chan[i].freq);
       if (chan[i].freq<1) chan[i].freq=1;
-      if (chan[i].freq>127) chan[i].freq=0;
+      if (chan[i].freq>127) chan[i].freq=127;
       if (isMuted[i]) chan[i].keyOn=false;
       if (chan[i].keyOn) {
         if (i<3) {
@@ -150,6 +152,7 @@ void DivPlatformVIC20::tick() {
 }
 
 int DivPlatformVIC20::dispatch(DivCommand c) {
+  int CHIP_DIVIDER=chipDividers[c.chan];
   switch (c.cmd) {
     case DIV_CMD_NOTE_ON: {
       DivInstrument* ins=parent->getIns(chan[c.chan].ins);