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105 lines
3.4 KiB
C++
105 lines
3.4 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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namespace InstructionSet {
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namespace M68k {
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struct Status {
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/* b15 */
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uint_fast32_t trace_flag_ = 0; // The trace flag is set if this value is non-zero.
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/* b13 */
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int is_supervisor_ = 0; // 1 => processor is in supervisor mode; 0 => it isn't.
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/* b7–b9 */
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int interrupt_level_ = 0; // The direct integer value of thee current interrupt level.
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/* b0–b4 */
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uint_fast32_t zero_result_ = 0; // The zero flag is set if this value is zero.
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uint_fast32_t carry_flag_ = 0; // The carry flag is set if this value is non-zero.
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uint_fast32_t extend_flag_ = 0; // The extend flag is set if this value is non-zero.
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uint_fast32_t overflow_flag_ = 0; // The overflow flag is set if this value is non-zero.
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uint_fast32_t negative_flag_ = 0; // The negative flag is set if 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_ ? 0x0001 : 0x0000) |
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(overflow_flag_ ? 0x0002 : 0x0000) |
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(zero_result_ ? 0x0000 : 0x0004) |
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(negative_flag_ ? 0x0008 : 0x0000) |
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(extend_flag_ ? 0x0010 : 0x0000);
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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_ ? 0x8000 : 0x0000) |
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(is_supervisor_ << 13)
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);
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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) & 0x0001;
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overflow_flag_ = (ccr) & 0x0002;
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zero_result_ = ((ccr) & 0x0004) ^ 0x0004;
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negative_flag_ = (ccr) & 0x0008;
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extend_flag_ = (ccr) & 0x0010;
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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 & 0x8000;
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is_supervisor_ = (status >> 13) & 1;
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return is_supervisor_;
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}
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/// Evaluates the condition described in the low four bits of @c code
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template <typename IntT> bool evaluate_condition(IntT code) {
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switch(code & 0xf) {
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default:
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case 0x00: return true; // true
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case 0x01: return false; // false
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case 0x02: return zero_result_ && !carry_flag_; // high
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case 0x03: return !zero_result_ || carry_flag_; // low or same
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case 0x04: return !carry_flag_; // carry clear
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case 0x05: return carry_flag_; // carry set
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case 0x06: return zero_result_; // not equal
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case 0x07: return !zero_result_; // equal
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case 0x08: return !overflow_flag_; // overflow clear
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case 0x09: return overflow_flag_; // overflow set
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case 0x0a: return !negative_flag_; // positive
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case 0x0b: return negative_flag_; // negative
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case 0x0c: // greater than or equal
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return (negative_flag_ && overflow_flag_) || (!negative_flag_ && !overflow_flag_);
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case 0x0d: // less than
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return (negative_flag_ && !overflow_flag_) || (!negative_flag_ && overflow_flag_);
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case 0x0e: // greater than
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return zero_result_ && ((negative_flag_ && overflow_flag_) || (!negative_flag_ && !overflow_flag_));
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case 0x0f: // less than or equal
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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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