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https://github.com/TomHarte/CLK.git
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130 lines
4.3 KiB
C++
130 lines
4.3 KiB
C++
//
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// Status.hpp
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// Clock Signal
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//
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// Created by Thomas Harte on 28/04/2022.
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// Copyright © 2022 Thomas Harte. All rights reserved.
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//
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#ifndef InstructionSets_M68k_Status_h
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#define InstructionSets_M68k_Status_h
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#include "Instruction.hpp"
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namespace InstructionSet {
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namespace M68k {
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namespace ConditionCode {
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static constexpr uint16_t Carry = 1 << 0;
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static constexpr uint16_t Overflow = 1 << 1;
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static constexpr uint16_t Zero = 1 << 2;
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static constexpr uint16_t Negative = 1 << 3;
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static constexpr uint16_t Extend = 1 << 4;
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static constexpr uint16_t AllConditions = Carry | Overflow | Zero | Negative | Extend;
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static constexpr uint16_t Supervisor = 1 << 13;
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static constexpr uint16_t Trace = 1 << 15;
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static constexpr uint16_t InterruptPriorityMask = 0b111 << 8;
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}
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struct Status {
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/// Generally holds an unevaluated flag for potential later lazy evaluation; it'll be zero for one outcome,
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/// non-zero for the other, but no guarantees are made about the potential range of non-zero values.
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using FlagT = uint_fast32_t;
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/* b15 */
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FlagT trace_flag = 0; // The trace flag is set if and only if this value is non-zero.
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/* b13 */
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bool is_supervisor = false; // true => processor is in supervisor mode; false => it isn't.
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/* b7–b9 */
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int interrupt_level = 0; // The direct integer value of the current interrupt level.
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// Values of 8 or greater have undefined meaning.
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/* b0–b4 */
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FlagT zero_result = 0; // The zero flag is set if and only if this value is zero.
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FlagT carry_flag = 0; // The carry flag is set if and only if this value is non-zero.
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FlagT extend_flag = 0; // The extend flag is set if and only if this value is non-zero.
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FlagT overflow_flag = 0; // The overflow flag is set if and only if this value is non-zero.
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FlagT negative_flag = 0; // The negative flag is set if and only this value is non-zero.
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/// Gets the current condition codes.
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constexpr uint16_t ccr() const {
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return
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(carry_flag ? ConditionCode::Carry : 0) |
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(overflow_flag ? ConditionCode::Overflow : 0) |
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(!zero_result ? ConditionCode::Zero : 0) |
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(negative_flag ? ConditionCode::Negative : 0) |
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(extend_flag ? ConditionCode::Extend : 0);
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}
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/// Sets the current condition codes.
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constexpr void set_ccr(uint16_t ccr) {
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carry_flag = ccr & ConditionCode::Carry;
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overflow_flag = ccr & ConditionCode::Overflow;
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zero_result = ~ccr & ConditionCode::Zero;
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negative_flag = ccr & ConditionCode::Negative;
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extend_flag = ccr & ConditionCode::Extend;
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}
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/// Gets the current value of the status register.
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constexpr uint16_t status() const {
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return uint16_t(
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ccr() |
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(interrupt_level << 8) |
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(trace_flag ? ConditionCode::Trace : 0) |
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(is_supervisor ? ConditionCode::Supervisor : 0)
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);
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}
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/// Sets the current value of the status register;
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/// @returns @c true if the processor finishes in supervisor mode; @c false otherwise.
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constexpr bool set_status(uint16_t status) {
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set_ccr(status);
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interrupt_level = (status >> 8) & 7;
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trace_flag = status & ConditionCode::Trace;
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is_supervisor = status & ConditionCode::Supervisor;
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return is_supervisor;
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}
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/// Evaluates @c condition.
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bool evaluate_condition(Condition condition) {
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switch(condition) {
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default:
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case Condition::True: return true;
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case Condition::False: return false;
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case Condition::High: return zero_result && !carry_flag;
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case Condition::LowOrSame: return !zero_result || carry_flag;
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case Condition::CarryClear: return !carry_flag;
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case Condition::CarrySet: return carry_flag;
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case Condition::NotEqual: return zero_result;
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case Condition::Equal: return !zero_result;
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case Condition::OverflowClear: return !overflow_flag;
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case Condition::OverflowSet: return overflow_flag;
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case Condition::Positive: return !negative_flag;
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case Condition::Negative: return negative_flag;
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case Condition::GreaterThanOrEqual:
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return (negative_flag && overflow_flag) || (!negative_flag && !overflow_flag);
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case Condition::LessThan:
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return (negative_flag && !overflow_flag) || (!negative_flag && overflow_flag);
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case Condition::GreaterThan:
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return zero_result && ((negative_flag && overflow_flag) || (!negative_flag && !overflow_flag));
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case Condition::LessThanOrEqual:
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return !zero_result || (negative_flag && !overflow_flag) || (!negative_flag && overflow_flag);
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}
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}
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};
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}
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}
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#endif /* InstructionSets_M68k_Status_h */
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