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231 lines
6.8 KiB
C++
231 lines
6.8 KiB
C++
//
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// Flags.hpp
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// Clock Signal
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//
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// Created by Thomas Harte on 05/10/2023.
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// Copyright © 2023 Thomas Harte. All rights reserved.
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//
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#pragma once
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#include "../../Numeric/Carry.hpp"
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namespace InstructionSet::x86 {
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namespace FlagValue {
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//
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// Standard flags.
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//
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static constexpr uint32_t Carry = 1 << 0;
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static constexpr uint32_t Parity = 1 << 2;
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static constexpr uint32_t AuxiliaryCarry = 1 << 4;
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static constexpr uint32_t Zero = 1 << 6;
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static constexpr uint32_t Sign = 1 << 7;
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static constexpr uint32_t Trap = 1 << 8;
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static constexpr uint32_t Interrupt = 1 << 9;
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static constexpr uint32_t Direction = 1 << 10;
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static constexpr uint32_t Overflow = 1 << 11;
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//
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// 80286+ additions.
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//
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static constexpr uint32_t IOPrivilege = (1 << 12) | (1 << 13);
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static constexpr uint32_t NestedTask = 1 << 14;
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//
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// 16-bit protected mode flags.
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//
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static constexpr uint32_t ProtectionEnable = 1 << 16;
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static constexpr uint32_t MonitorProcessorExtension = 1 << 17;
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static constexpr uint32_t ProcessorExtensionExtension = 1 << 18;
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static constexpr uint32_t TaskSwitch = 1 << 19;
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//
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// 32-bit protected mode flags.
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//
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static constexpr uint32_t Resume = 1 << 16;
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static constexpr uint32_t VirtualMode = 1 << 17;
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}
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enum class Flag {
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Carry,
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AuxiliaryCarry,
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Sign,
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Overflow,
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Trap,
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Interrupt,
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Direction,
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Zero,
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ParityOdd
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};
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enum class Condition {
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Overflow,
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Below,
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Zero,
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BelowOrEqual,
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Sign,
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ParityOdd,
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Less,
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LessOrEqual
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};
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class Flags {
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public:
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using FlagT = uint32_t;
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// Flag getters.
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template <Flag flag_v> bool flag() const {
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switch(flag_v) {
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case Flag::Carry: return carry_;
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case Flag::AuxiliaryCarry: return auxiliary_carry_;
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case Flag::Sign: return sign_;
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case Flag::Overflow: return overflow_;
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case Flag::Trap: return trap_;
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case Flag::Interrupt: return interrupt_;
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case Flag::Direction: return direction_ < 0;
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case Flag::Zero: return !zero_;
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case Flag::ParityOdd: return not_parity_bit();
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}
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}
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// Condition evaluation.
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template <Condition test> bool condition() const {
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switch(test) {
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case Condition::Overflow: return flag<Flag::Overflow>();
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case Condition::Below: return flag<Flag::Carry>();
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case Condition::Zero: return flag<Flag::Zero>();
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case Condition::BelowOrEqual: return flag<Flag::Zero>() || flag<Flag::Carry>();
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case Condition::Sign: return flag<Flag::Sign>();
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case Condition::ParityOdd: return flag<Flag::ParityOdd>();
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case Condition::Less: return flag<Flag::Sign>() != flag<Flag::Overflow>();
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case Condition::LessOrEqual: return flag<Flag::Zero>() || flag<Flag::Sign>() != flag<Flag::Overflow>();
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}
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}
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// Convenience setters.
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/// Sets all of @c flags as a function of @c value:
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/// • Flag::Zero: sets the zero flag if @c value is zero;
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/// • Flag::Sign: sets the sign flag if the top bit of @c value is one;
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/// • Flag::ParityOdd: sets parity based on the low 8 bits of @c value;
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/// • Flag::Carry: sets carry if @c value is non-zero;
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/// • Flag::AuxiliaryCarry: sets auxiliary carry if @c value is non-zero;
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/// • Flag::Overflow: sets overflow if @c value is non-zero;
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/// • Flag::Interrupt: sets interrupt if @c value is non-zero;
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/// • Flag::Trap: sets interrupt if @c value is non-zero;
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/// • Flag::Direction: sets direction if @c value is non-zero.
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template <typename IntT, Flag... flags> void set_from(IntT value) {
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for(const auto flag: {flags...}) {
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switch(flag) {
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default: break;
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case Flag::Zero: zero_ = value; break;
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case Flag::Sign: sign_ = value & Numeric::top_bit<IntT>(); break;
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case Flag::ParityOdd: parity_ = value; break;
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case Flag::Carry: carry_ = value; break;
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case Flag::AuxiliaryCarry: auxiliary_carry_ = value; break;
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case Flag::Overflow: overflow_ = value; break;
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case Flag::Interrupt: interrupt_ = value; break;
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case Flag::Trap: trap_ = value; break;
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case Flag::Direction: direction_ = value ? -1 : 1; break;
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}
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}
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}
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template <Flag... flags> void set_from(FlagT value) {
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set_from<FlagT, flags...>(value);
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}
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template <typename IntT> IntT carry_bit() const { return carry_ ? 1 : 0; }
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bool not_parity_bit() const {
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// x86 parity always considers the lowest 8-bits only.
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auto result = static_cast<uint8_t>(parity_);
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result ^= result >> 4;
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result ^= result >> 2;
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result ^= result >> 1;
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return result & 1;
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}
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template <typename IntT> IntT direction() const { return static_cast<IntT>(direction_); }
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// Complete value get and set.
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void set(uint16_t value) {
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set_from<Flag::Carry>(value & FlagValue::Carry);
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set_from<Flag::AuxiliaryCarry>(value & FlagValue::AuxiliaryCarry);
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set_from<Flag::Overflow>(value & FlagValue::Overflow);
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set_from<Flag::Trap>(value & FlagValue::Trap);
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set_from<Flag::Interrupt>(value & FlagValue::Interrupt);
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set_from<Flag::Direction>(value & FlagValue::Direction);
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set_from<uint8_t, Flag::Sign>(uint8_t(value));
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set_from<Flag::Zero>((~value) & FlagValue::Zero);
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set_from<Flag::ParityOdd>((~value) & FlagValue::Parity);
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}
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uint16_t get() const {
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return
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0xf002 |
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(flag<Flag::Carry>() ? FlagValue::Carry : 0) |
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(flag<Flag::AuxiliaryCarry>() ? FlagValue::AuxiliaryCarry : 0) |
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(flag<Flag::Sign>() ? FlagValue::Sign : 0) |
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(flag<Flag::Overflow>() ? FlagValue::Overflow : 0) |
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(flag<Flag::Trap>() ? FlagValue::Trap : 0) |
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(flag<Flag::Interrupt>() ? FlagValue::Interrupt : 0) |
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(flag<Flag::Direction>() ? FlagValue::Direction : 0) |
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(flag<Flag::Zero>() ? FlagValue::Zero : 0) |
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(flag<Flag::ParityOdd>() ? 0 : FlagValue::Parity);
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}
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std::string to_string() const {
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std::string result;
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if(flag<Flag::Overflow>()) result += "O"; else result += "-";
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if(flag<Flag::Direction>()) result += "D"; else result += "-";
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if(flag<Flag::Interrupt>()) result += "I"; else result += "-";
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if(flag<Flag::Trap>()) result += "T"; else result += "-";
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if(flag<Flag::Sign>()) result += "S"; else result += "-";
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if(flag<Flag::Zero>()) result += "Z"; else result += "-";
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result += "-";
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if(flag<Flag::AuxiliaryCarry>()) result += "A"; else result += "-";
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result += "-";
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if(!flag<Flag::ParityOdd>()) result += "P"; else result += "-";
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result += "-";
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if(flag<Flag::Carry>()) result += "C"; else result += "-";
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return result;
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}
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bool operator ==(const Flags &rhs) const {
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return get() == rhs.get();
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}
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private:
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// Non-zero => set; zero => unset.
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uint32_t carry_;
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uint32_t auxiliary_carry_;
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uint32_t sign_;
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uint32_t overflow_;
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uint32_t trap_;
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uint32_t interrupt_;
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// +1 = direction flag not set;
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// -1 = direction flag set.
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int32_t direction_;
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// Zero => set; non-zero => unset.
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uint32_t zero_;
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// Odd number of bits => set; even => unset.
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uint32_t parity_;
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};
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}
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