prepare to use FixedQueue

avoiding allocations in real-time code

src/engine/fixedQueue.h

@@ -0,0 +1,81 @@
+/**
+ * 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 _FIXED_QUEUE_H
+#define _FIXED_QUEUE_H
+
+#include <stdint.h>
+#include "../ta-log.h"
+
+template<typename T, size_t items> struct FixedQueue {
+  size_t readPos, writePos;
+  T data[items];
+
+  T& front();
+  bool pop();
+  bool push(const T& item);
+  void clear();
+  bool empty();
+  size_t size();
+  FixedQueue():
+    readPos(0),
+    writePos(0) {}
+};
+
+template <typename T, size_t items> T& FixedQueue<T,items>::front() {
+  return data[readPos];
+}
+
+template <typename T, size_t items> bool FixedQueue<T,items>::pop() {
+  if (readPos==writePos) return false;
+  if (++readPos>=items) readPos=0;
+  return true;
+}
+
+template <typename T, size_t items> bool FixedQueue<T,items>::push(const T& item) {
+  if (writePos==(readPos-1)) {
+    logW("queue overflow!");
+    return false;
+  }
+  if (writePos==0 && readPos==items-1) {
+    logW("queue overflow!");
+    return false;
+  }
+  data[writePos]=item;
+  if (++writePos>=items) writePos=0;
+  return true;
+}
+
+template <typename T, size_t items> void FixedQueue<T,items>::clear() {
+  readPos=0;
+  writePos=0;
+}
+
+template <typename T, size_t items> bool FixedQueue<T,items>::empty() {
+  return (readPos==writePos);
+}
+
+template <typename T, size_t items> size_t FixedQueue<T,items>::size() {
+  if (readPos>writePos) {
+    return items+writePos-readPos;
+  }
+  return writePos-readPos;
+}
+
+#endif

src/engine/platform/pce.cpp

@@ -22,7 +22,7 @@
 #include <math.h>
 
 //#define rWrite(a,v) pendingWrites[a]=v;
-#define rWrite(a,v) if (!skipRegisterWrites) {writes.emplace(a,v); if (dumpWrites) {addWrite(a,v);} }
+#define rWrite(a,v) if (!skipRegisterWrites) {writes.push(QueuedWrite(a,v)); if (dumpWrites) {addWrite(a,v);} }
 #define chWrite(c,a,v) \
   if (!skipRegisterWrites) { \
     if (curChan!=c) { \

src/engine/platform/pce.h

@@ -21,7 +21,7 @@
 #define _PCE_H
 
 #include "../dispatch.h"
-#include <queue>
+#include "../fixedQueue.h"
 #include "../waveSynth.h"
 #include "sound/pce_psg.h"
 
@@ -62,9 +62,10 @@ class DivPlatformPCE: public DivDispatch {
   struct QueuedWrite {
       unsigned char addr;
       unsigned char val;
+      QueuedWrite(): addr(0), val(9) {}
       QueuedWrite(unsigned char a, unsigned char v): addr(a), val(v) {}
   };
-  std::queue<QueuedWrite> writes;
+  FixedQueue<QueuedWrite,512> writes;
   unsigned char lastPan;
 
   int cycles, curChan, delay;