Makes an effort to factor out the 6502's [lazy] flags.

This is preparatory to deciding which instructions, if any, are worth factoring out.

Processors/6502Esque/Implementation/LazyFlags.hpp

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+//
+//  LazyFlags.hpp
+//  Clock Signal
+//
+//  Created by Thomas Harte on 05/10/2020.
+//  Copyright © 2020 Thomas Harte. All rights reserved.
+//
+
+#ifndef LazyFlags_h
+#define LazyFlags_h
+
+#include "../6502Esque.hpp"
+
+namespace CPU {
+namespace MOS6502Esque {
+
+struct LazyFlags {
+	/// Bit 7 is set if the negative flag is set; otherwise it is clear.
+	uint8_t negative_result;
+
+	/// Non-zero if the zero flag is clear, zero if it is set.
+	uint8_t zero_result;
+
+	/// Contains Flag::Carry.
+	uint8_t carry;
+
+	/// Contains Flag::Decimal.
+	uint8_t decimal;
+
+	/// Contains Flag::Overflow.
+	uint8_t overflow;
+
+	/// Contains Flag::Interrupt, complemented.
+	uint8_t inverse_interrupt = 0;
+
+	void set_nz(uint8_t value) {
+		zero_result = negative_result = value;
+	}
+
+	void set(uint8_t flags) {
+		carry				= flags		& Flag::Carry;
+		negative_result		= flags		& Flag::Sign;
+		zero_result			= (~flags)	& Flag::Zero;
+		overflow			= flags		& Flag::Overflow;
+		inverse_interrupt	= (~flags)	& Flag::Interrupt;
+		decimal				= flags		& Flag::Decimal;
+	}
+
+	uint8_t get() const {
+		return carry | overflow | (inverse_interrupt ^ Flag::Interrupt) | (negative_result & 0x80) | (zero_result ? 0 : Flag::Zero) | Flag::Always | decimal;
+	}
+
+	LazyFlags() {
+		// Only the interrupt flag is defined upon reset but get_flags isn't going to
+		// mask the other flags so we need to do that, at least.
+		carry &= Flag::Carry;
+		decimal &= Flag::Decimal;
+		overflow &= Flag::Overflow;
+	}
+};
+
+
+}
+}
+
+#endif /* LazyFlags_h */