blip_buf clock<rate bug workaround, part 1

issue #1055
now I gotta think of a strategy for dispatch

src/engine/engine.cpp

@@ -2668,10 +2668,17 @@ void DivEngine::previewSampleNoLock(int sample, int note, int pStart, int pEnd)
     if (rate<=0) rate=song.sample[sample]->centerRate;
   }
   if (rate<100) rate=100;
+  double rateOrig=rate;
+  sPreview.rateMul=1;
+  while (sPreview.rateMul<0x40000000 && rate<got.rate) {
+    sPreview.rateMul<<=1;
+    rate*=2.0;
+  }
   blip_set_rates(samp_bb,rate,got.rate);
   samp_prevSample=0;
-  sPreview.rate=rate;
+  sPreview.rate=rateOrig;
   sPreview.pos=(sPreview.pBegin>=0)?sPreview.pBegin:0;
+  sPreview.posSub=0;
   sPreview.sample=sample;
   sPreview.wave=-1;
   sPreview.dir=false;
@@ -2696,10 +2703,17 @@ void DivEngine::previewWaveNoLock(int wave, int note) {
   blip_clear(samp_bb);
   double rate=song.wave[wave]->len*((song.tuning*0.0625)*pow(2.0,(double)(note+3)/12.0));
   if (rate<100) rate=100;
+  double rateOrig=rate;
+  sPreview.rateMul=1;
+  while (sPreview.rateMul<0x40000000 && rate<got.rate) {
+    sPreview.rateMul<<=1;
+    rate*=2.0;
+  }
   blip_set_rates(samp_bb,rate,got.rate);
   samp_prevSample=0;
-  sPreview.rate=rate;
+  sPreview.rate=rateOrig;
   sPreview.pos=0;
+  sPreview.posSub=0;
   sPreview.sample=-1;
   sPreview.wave=wave;
   sPreview.dir=false;

src/engine/engine.h

@@ -414,6 +414,7 @@ class DivEngine {
     int wave;
     int pos;
     int pBegin, pEnd;
+    int rateMul, posSub;
     bool dir;
     SamplePreview():
       rate(0.0),
@@ -422,6 +423,8 @@ class DivEngine {
       pos(0),
       pBegin(-1),
       pEnd(-1),
+      rateMul(1),
+      posSub(0),
       dir(false) {}
   } sPreview;
 

src/engine/playback.cpp

@@ -1541,10 +1541,13 @@ void DivEngine::nextBuf(float** in, float** out, int inChans, int outChans, unsi
           samp_temp=0;
         } else {
           samp_temp=s->data16[sPreview.pos];
-          if (sPreview.dir) {
-            sPreview.pos--;
-          } else {
-            sPreview.pos++;
+          if (--sPreview.posSub<=0) {
+            sPreview.posSub=sPreview.rateMul;
+            if (sPreview.dir) {
+              sPreview.pos--;
+            } else {
+              sPreview.pos++;
+            }
           }
         }
         blip_add_delta(samp_bb,i,samp_temp-samp_prevSample);
@@ -1649,8 +1652,11 @@ void DivEngine::nextBuf(float** in, float** out, int inChans, int outChans, unsi
         } else {
           samp_temp=((MIN(wave->data[sPreview.pos],wave->max)<<14)/wave->max)-8192;
         }
-        if (++sPreview.pos>=wave->len) {
-          sPreview.pos=0;
+        if (--sPreview.posSub<=0) {
+          sPreview.posSub=sPreview.rateMul;
+          if (++sPreview.pos>=wave->len) {
+            sPreview.pos=0;
+          }
         }
         blip_add_delta(samp_bb,i,samp_temp-samp_prevSample);
         samp_prevSample=samp_temp;