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78 lines
2.2 KiB
C++
78 lines
2.2 KiB
C++
//
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// LazyFlags.hpp
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// Clock Signal
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//
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// Created by Thomas Harte on 05/10/2020.
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// Copyright © 2020 Thomas Harte. All rights reserved.
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//
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#pragma once
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#include "../6502Esque.hpp"
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namespace CPU::MOS6502Esque {
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struct LazyFlags {
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/// Bit 7 is set if the negative flag is set; otherwise it is clear.
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uint8_t negative_result = 0;
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/// Non-zero if the zero flag is clear, zero if it is set.
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uint8_t zero_result = 0;
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/// Contains Flag::Carry.
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uint8_t carry = 0;
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/// Contains Flag::Decimal.
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uint8_t decimal = 0;
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/// Contains Flag::Overflow.
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uint8_t overflow = 0;
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/// Contains Flag::Interrupt, complemented.
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uint8_t inverse_interrupt = 0;
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/// Sets N and Z flags per the 8-bit value @c value.
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void set_nz(uint8_t value) {
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zero_result = negative_result = value;
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}
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/// Sets N and Z flags per the 8- or 16-bit value @c value; @c shift should be 0 to indicate an 8-bit value or 8 to indicate a 16-bit value.
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void set_nz(uint16_t value, int shift) {
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negative_result = uint8_t(value >> shift);
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zero_result = uint8_t(value | (value >> shift));
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}
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/// Sets the Z flag per the 8- or 16-bit value @c value; @c shift should be 0 to indicate an 8-bit value or 8 to indicate a 16-bit value.
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void set_z(uint16_t value, int shift) {
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zero_result = uint8_t(value | (value >> shift));
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}
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/// Sets the N flag per the 8- or 16-bit value @c value; @c shift should be 0 to indicate an 8-bit value or 8 to indicate a 16-bit value.
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void set_n(uint16_t value, int shift) {
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negative_result = uint8_t(value >> shift);
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}
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void set(uint8_t flags) {
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carry = flags & Flag::Carry;
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negative_result = flags & Flag::Sign;
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zero_result = (~flags) & Flag::Zero;
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overflow = flags & Flag::Overflow;
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inverse_interrupt = (~flags) & Flag::Interrupt;
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decimal = flags & Flag::Decimal;
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}
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uint8_t get() const {
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return carry | overflow | (inverse_interrupt ^ Flag::Interrupt) | (negative_result & 0x80) | (zero_result ? 0 : Flag::Zero) | Flag::Always | Flag::Break | decimal;
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}
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LazyFlags() {
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// Only the interrupt flag is defined upon reset but get_flags isn't going to
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// mask the other flags so we need to do that, at least.
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carry &= Flag::Carry;
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decimal &= Flag::Decimal;
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overflow &= Flag::Overflow;
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}
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};
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}
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