Introduce SizedCounter as start of CRTC reworking.

Numeric/SizedCounter.hpp

@@ -0,0 +1,65 @@
+//
+//  SizedCounter.hpp
+//  Clock Signal
+//
+//  Created by Thomas Harte on 22/09/2025.
+//  Copyright © 2025 Thomas Harte. All rights reserved.
+//
+
+#pragma once
+
+#include "Sizes.hpp"
+
+namespace Numeric {
+
+/*!
+	Provides a counter that is strictly limited to the requested of bits but attempts otherwise
+	to act like a standard C++ numeric type.
+*/
+template <int bits>
+struct SizedCounter {
+	using IntT = MinIntForValue<1 << bits>::type;
+	inline static constexpr IntT Mask = (1 << bits) - 1;
+
+	constexpr SizedCounter(const IntT start_value) noexcept : counter_(start_value & Mask) {}
+	SizedCounter() = default;
+
+	operator IntT() const {
+		return counter_;
+	}
+
+	SizedCounter &operator++(int) {
+		(*this) ++;
+		return *this;
+	}
+
+	SizedCounter &operator++() {
+		counter_ = (counter_ + 1) & Mask;
+		return *this;
+	}
+
+	SizedCounter &operator+=(const IntT rhs) {
+		counter_ = (counter_ + rhs) & Mask;
+		return *this;
+	}
+
+	auto operator <=>(const SizedCounter &) const = default;
+
+	/// Replaces the bits in the range [begin, end) with those in the low-order bits of @c vlaue.
+	template <int begin, int end>
+	void load(const MinIntForValue<1 << (end - begin)>::type value) {
+		const auto mask = (1 << end) - (1 << begin);
+		counter_ &= ~mask;
+		counter_ |= IntT((value << begin) & mask);
+	}
+
+	template <int begin, typename IntT>
+	void load(const IntT value) {
+		load<begin, begin + sizeof(IntT)*8>(value);
+	}
+
+private:
+	IntT counter_{};
+};
+
+}