add experimental command stream player

for verification

after that I am going to write optimization code

src/engine/cmdStream.h

@@ -0,0 +1,59 @@
+/**
+ * Furnace Tracker - multi-system chiptune tracker
+ * Copyright (C) 2021-2023 tildearrow and contributors
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#ifndef _CMD_STREAM_H
+#define _CMD_STREAM_H
+
+#include "defines.h"
+#include "safeReader.h"
+
+class DivEngine;
+
+struct DivCSChannelState {
+  unsigned int readPos;
+  int waitTicks;
+
+  int volume, volMax, volSpeed;
+
+  DivCSChannelState():
+    readPos(0),
+    waitTicks(0),
+    volume(0x7f00),
+    volMax(0),
+    volSpeed(0) {}
+};
+
+class DivCSPlayer {
+  DivEngine* e;
+  unsigned char* b;
+  SafeReader stream;
+  DivCSChannelState chan[DIV_MAX_CHANS];
+  unsigned char fastDelays[16];
+  unsigned char fastCmds[16];
+  public:
+    void cleanup();
+    bool tick();
+    bool init();
+    DivCSPlayer(DivEngine* en, unsigned char* buf, size_t len):
+      e(en),
+      b(buf),
+      stream(buf,len) {}
+};
+
+#endif