From 6a15bb15ca2b104d3cf2261ff530983c7c84f237 Mon Sep 17 00:00:00 2001
From: Thomas Harte <thomas.harte@gmail.com>
Date: Sat, 7 Aug 2021 17:29:21 -0400
Subject: [PATCH] Adds a simpler way of deferring single values.

---
 ClockReceiver/DeferredValue.hpp               | 48 +++++++++++++++++++
 .../Clock Signal.xcodeproj/project.pbxproj    |  2 +
 2 files changed, 50 insertions(+)
 create mode 100644 ClockReceiver/DeferredValue.hpp

diff --git a/ClockReceiver/DeferredValue.hpp b/ClockReceiver/DeferredValue.hpp
new file mode 100644
index 000000000..35fbdf974
--- /dev/null
+++ b/ClockReceiver/DeferredValue.hpp
@@ -0,0 +1,48 @@
+//
+//  DeferredValue.hpp
+//  Clock Signal
+//
+//  Created by Thomas Harte on 07/08/2021.
+//  Copyright © 2021 Thomas Harte. All rights reserved.
+//
+
+#ifndef DeferredValue_h
+#define DeferredValue_h
+
+/*!
+	Provides storage for a single deferred value: one with a current value and a certain number
+	of future values.
+*/
+template <int DeferredDepth, typename ValueT> class DeferredValue {
+	private:
+		static_assert(sizeof(ValueT) <= 4);
+
+		constexpr int elements_per_uint32 = sizeof(uint32_t) / sizeof(ValueT);
+		constexpr int unit_shift = sizeof(ValueT) * 8;
+		constexpr int insert_shift = (DeferredDepth & (elements_per_uint32 - 1)) * unit_shift;
+		constexpr uint32_t insert_mask = ~(0xffff'ffff << insert_shift);
+
+		std::array<uint32_t, (DeferredDepth + elements_per_uint32 - 1) / elements_per_uint32> backlog;
+
+	public:
+		/// @returns the current value.
+		ValueT value() const {
+			return uint8_t(backlog[0]);
+		}
+
+		/// Advances to the next enqueued value.
+		void advance() {
+			for(size_t c = 0; c < backlog.size() - 1; c--) {
+				backlog[c] = (backlog[c] >> unit_shift) | (backlog[c+1] << (32 - unit_shift));
+			}
+			backlog[backlog.size() - 1] >>= unit_shift;
+		}
+
+		/// Inserts a new value, replacing whatever is currently at the end of the queue.
+		void insert(ValueT value) {
+			backlog[DeferredDepth / elements_per_uint32] =
+				(backlog[DeferredDepth / elements_per_uint32] & insert_mask) | (value << insert_shift);
+		}
+};
+
+#endif /* DeferredValue_h */
diff --git a/OSBindings/Mac/Clock Signal.xcodeproj/project.pbxproj b/OSBindings/Mac/Clock Signal.xcodeproj/project.pbxproj
index 1713b31bb..8fa9ea1c8 100644
--- a/OSBindings/Mac/Clock Signal.xcodeproj/project.pbxproj	
+++ b/OSBindings/Mac/Clock Signal.xcodeproj/project.pbxproj	
@@ -1585,6 +1585,7 @@
 		4B98A0601FFADCDE00ADF63B /* MSXStaticAnalyserTests.mm */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.objcpp; path = MSXStaticAnalyserTests.mm; sourceTree = "<group>"; };
 		4B98A1CD1FFADEC400ADF63B /* MSX ROMs */ = {isa = PBXFileReference; lastKnownFileType = folder; path = "MSX ROMs"; sourceTree = "<group>"; };
 		4B996B2D2496DAC2001660EF /* VSyncPredictor.hpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.h; path = VSyncPredictor.hpp; sourceTree = "<group>"; };
+		4B99EBD026BF2D9F00CA924D /* DeferredValue.hpp */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.h; path = DeferredValue.hpp; sourceTree = "<group>"; };
 		4B9BE3FE203A0C0600FFAE60 /* MultiSpeaker.cpp */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.cpp; path = MultiSpeaker.cpp; sourceTree = "<group>"; };
 		4B9BE3FF203A0C0600FFAE60 /* MultiSpeaker.hpp */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.h; path = MultiSpeaker.hpp; sourceTree = "<group>"; };
 		4B9D0C4A22C7D70900DE1AD3 /* 68000BCDTests.mm */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.objcpp; path = 68000BCDTests.mm; sourceTree = "<group>"; };
@@ -4733,6 +4734,7 @@
 				4B644ED023F0FB55006C0CC5 /* ScanSynchroniser.hpp */,
 				4B449C942063389900A095C8 /* TimeTypes.hpp */,
 				4B996B2D2496DAC2001660EF /* VSyncPredictor.hpp */,
+				4B99EBD026BF2D9F00CA924D /* DeferredValue.hpp */,
 			);
 			name = ClockReceiver;
 			path = ../../ClockReceiver;