Merged revision(s) 20662 from trunk/OpenMPT:

[Fix] Opal: With mix rates exceeding 131kHz, it was possible that the interpolated output overflowed. The new linear interpolation is based on OpenMPT's own mixer code, and may also be slightly faster because it divides by SampleRate only once (https://bugs.openmpt.org/view.php?id=1775).
........


git-svn-id: https://source.openmpt.org/svn/openmpt/branches/OpenMPT-1.31@20663 56274372-70c3-4bfc-bfc3-4c3a0b034d27

soundlib/opal.h

@@ -22,6 +22,7 @@
 
 
 #include <cstdint>
+#include "../common/mptBaseUtils.h"
 
 
 
@@ -574,9 +575,9 @@ void Opal::Sample(int16_t *left, int16_t *right) {
     }
 
     // Mix with the partial accumulation
-    int32_t omblend = SampleRate - SampleAccum;
-    *left = static_cast<uint16_t>((LastOutput[0] * omblend + CurrOutput[0] * SampleAccum) / SampleRate);
-    *right = static_cast<uint16_t>((LastOutput[1] * omblend + CurrOutput[1] * SampleAccum) / SampleRate);
+    const int32_t fract = Util::muldivr(SampleAccum, 65536, SampleRate);
+    *left = static_cast<int16_t>(LastOutput[0] + ((fract * (CurrOutput[0] - LastOutput[0])) / 65536));
+    *right = static_cast<int16_t>(LastOutput[1] + ((fract * (CurrOutput[1] - LastOutput[1])) / 65536));
 
     SampleAccum += OPL3SampleRate;
 }
@@ -606,14 +607,14 @@ void Opal::Output(int16_t &left, int16_t &right) {
     else if (leftmix > 0x7FFF)
         left = 0x7FFF;
     else
-        left = static_cast<uint16_t>(leftmix);
+        left = static_cast<int16_t>(leftmix);
 
     if (rightmix < -0x8000)
         right = -0x8000;
     else if (rightmix > 0x7FFF)
         right = 0x7FFF;
     else
-        right = static_cast<uint16_t>(rightmix);
+        right = static_cast<int16_t>(rightmix);
 
     Clock++;