From 4bf4be1ea26c3da3cc914e29f667a99fc35bdadd Mon Sep 17 00:00:00 2001
From: Natt Akuma <akumanatt925@gmail.com>
Date: Wed, 22 Jun 2022 21:55:31 +0700
Subject: [PATCH] Fix 16-bit samples in YMZ280B VGM export

---
 src/engine/sample.h   |  1 +
 src/engine/vgmOps.cpp | 23 ++++++++++++++++++++++-
 2 files changed, 23 insertions(+), 1 deletion(-)

diff --git a/src/engine/sample.h b/src/engine/sample.h
index d9ad633c9..70f8418cf 100644
--- a/src/engine/sample.h
+++ b/src/engine/sample.h
@@ -248,6 +248,7 @@ struct DivSample {
     offQSound(0),
     offX1_010(0),
     offSU(0),
+    offYMZ280B(0),
     offRF5C68(0),
     samples(0) {}
   ~DivSample();
diff --git a/src/engine/vgmOps.cpp b/src/engine/vgmOps.cpp
index 6e2bc82cf..0d1ad4f52 100644
--- a/src/engine/vgmOps.cpp
+++ b/src/engine/vgmOps.cpp
@@ -1653,13 +1653,34 @@ SafeWriter* DivEngine::saveVGM(bool* sysToExport, bool loop, int version) {
       w->write(writeX1010[i]->getSampleMem(),writeX1010[i]->getSampleMemUsage());
     }
     if (writeZ280[i]!=NULL && writeZ280[i]->getSampleMemUsage()>0) {
+      // In VGM, YMZ280B's 16-bit PCM has an endianness swapped
+      // which have been fixed in the upstream MAME since 2013
+      // in order to get Konami FireBeat working
+      // The reason given for VGM not applying this change was
+      // "It matches OPL4 and MAME probably did an endianness optimization"
+      size_t sampleMemLen=writeZ280[i]->getSampleMemUsage();
+      unsigned char* sampleMem=new unsigned char[sampleMemLen];
+      memcpy(sampleMem,writeZ280[i]->getSampleMem(),sampleMemLen);
+      for (int i=0; i<song.sampleLen; i++) {
+        DivSample* s=song.sample[i];
+        if (s->depth==16) {
+          unsigned int pos=s->offYMZ280B;
+          for (unsigned int j=0; j<s->samples; j++) {
+            unsigned char lo=sampleMem[pos+j*2];
+            unsigned char hi=sampleMem[pos+j*2+1];
+            sampleMem[pos+j*2]=hi;
+            sampleMem[pos+j*2+1]=lo;
+          }
+        }
+      }
       w->writeC(0x67);
       w->writeC(0x66);
       w->writeC(0x86);
       w->writeI((writeZ280[i]->getSampleMemUsage()+8)|(i*0x80000000));
       w->writeI(writeZ280[i]->getSampleMemCapacity());
       w->writeI(0);
-      w->write(writeZ280[i]->getSampleMem(),writeZ280[i]->getSampleMemUsage());
+      w->write(sampleMem,sampleMemLen);
+      delete[] sampleMem;
     }
   }