Factor out the stuff of being a circular counter.

Numeric/CircularCounter.hpp

@@ -0,0 +1,48 @@
+//
+//  CircularCounter.hpp
+//  Clock Signal
+//
+//  Created by Thomas Harte on 15/02/2026.
+//  Copyright © 2026 Thomas Harte. All rights reserved.
+//
+
+#include <cassert>
+
+namespace Numeric {
+
+template <typename IntT, IntT limit>
+class CircularCounter {
+public:
+	constexpr CircularCounter() noexcept = default;
+	constexpr CircularCounter(const IntT value) noexcept : value_(value) {
+		assert(value < limit);
+	}
+
+	CircularCounter &operator ++() {
+		++value_;
+		if(value_ == limit) {
+			value_ = 0;
+		}
+		return *this;
+	}
+
+	CircularCounter operator ++(int) {
+		const auto result = *this;
+		++*this;
+		return result;
+	}
+
+	operator IntT() const {
+		return value_;
+	}
+
+	CircularCounter &operator = (const IntT rhs) {
+		value_ = rhs;
+		return *this;
+	}
+
+private:
+	IntT value_{};
+};
+
+}

OSBindings/Mac/Clock Signal.xcodeproj/project.pbxproj

@@ -1505,6 +1505,7 @@
 		4B228CD724DA12C50077EF25 /* CSScanTargetView.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = CSScanTargetView.h; sourceTree = "<group>"; };
 		4B228CD824DA12C60077EF25 /* CSScanTargetView.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; path = CSScanTargetView.m; sourceTree = "<group>"; };
 		4B24095A1C45DF85004DA684 /* Stepper.hpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.h; path = Stepper.hpp; sourceTree = "<group>"; };
+		4B249EDE2F4241DA00FD485B /* CircularCounter.hpp */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.h; path = CircularCounter.hpp; sourceTree = "<group>"; };
 		4B2530F3244E6773007980BF /* fm.json */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = text.json; path = fm.json; sourceTree = "<group>"; };
 		4B25BC1E2DDD64AA002044CA /* TaskStateSegment.hpp */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.h; path = TaskStateSegment.hpp; sourceTree = "<group>"; };
 		4B262BFF29691F55002EC0F7 /* PersonalityTraits.hpp */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.h; path = PersonalityTraits.hpp; sourceTree = "<group>"; };
@@ -3844,6 +3845,7 @@
 				4BD155312716362A00410C6E /* BitSpread.hpp */,
 				4B0B239F2D658C9400153879 /* BitStream.hpp */,
 				4281572E2AA0334300E16AA1 /* Carry.hpp */,
+				4B249EDE2F4241DA00FD485B /* CircularCounter.hpp */,
 				4B7BA03E23D55E7900B98D9E /* CRC.hpp */,
 				4BC3A9A52F15EF2D00ACC885 /* CubicCurve.hpp */,
 				4B7BA03F23D55E7900B98D9E /* LFSR.hpp */,

Outputs/ScanTargets/BufferingScanTarget.cpp

@@ -225,12 +225,12 @@ void BufferingScanTarget::announce(
 		const auto submit_pointers = submit_pointers_.load(std::memory_order_relaxed);
 		frames_[write].first_line = submit_pointers.line;
 		frames_[write].first_scan = submit_pointers.scan;
-		write = (write + 1) % frames_.size();
+		++write;
 		frame_write_.store(write, std::memory_order_release);
 
 		auto read = frame_read_.load(std::memory_order_relaxed);
 		if(read == write) {
-			read = (read + 1) % frames_.size();
+			++read;
 			frame_read_.store(read, std::memory_order_relaxed);
 		}
 	}

Outputs/ScanTargets/BufferingScanTarget.hpp

@@ -11,6 +11,7 @@
 #include "Outputs/ScanTarget.hpp"
 #include "Outputs/DisplayMetrics.hpp"
 #include "Concurrency/SpinLock.hpp"
+#include "Numeric/CircularCounter.hpp"
 
 #include <array>
 #include <atomic>
@@ -320,9 +321,10 @@ private:
 		size_t first_line;
 		bool previous_frame_was_complete;
 	};
-	std::array<Frame, 15> frames_;
-	std::atomic<size_t> frame_read_ = 0;
-	std::atomic<size_t> frame_write_ = 0;
+	static constexpr uint16_t NumFrames = 60;
+	std::array<Frame, NumFrames> frames_;
+	std::atomic<Numeric::CircularCounter<uint16_t, NumFrames>> frame_read_;
+	std::atomic<Numeric::CircularCounter<uint16_t, NumFrames>> frame_write_;
 
 
 	// By convention everything in the PointerSet points to the next instance