Lib65816/src/opcodes/OpCode_CMP.cpp

/*
 * This file is part of the 65816 Emulator Library.
 * Copyright (c) 2018 Francesco Rigoni.
 *
 * https://github.com/FrancescoRigoni/Lib65816
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, version 3.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program. If not, see <http://www.gnu.org/licenses/>.
 */

#include "../Cpu65816.hpp"

#define LOG_TAG "Cpu::executeCMP"

/**
 * This file contains the implementation for all CMP OpCodes
 */

void Cpu65816::execute8BitCMP(OpCode &opCode) {
    Address valueAddress = getAddressOfOpCodeData(opCode);
    uint8_t value = mSystemBus.readByte(valueAddress);
    uint8_t result = Binary::lower8BitsOf(mA) - value;
    mCpuStatus.updateSignAndZeroFlagFrom8BitValue(result);
    if (Binary::lower8BitsOf(mA) >= value) {
        mCpuStatus.setCarryFlag();
    } else {
        mCpuStatus.clearCarryFlag();
    }
}

void Cpu65816::execute16BitCMP(OpCode &opCode) {
    Address valueAddress = getAddressOfOpCodeData(opCode);
    uint16_t value = mSystemBus.readTwoBytes(valueAddress);
    uint16_t result = mA - value;
    mCpuStatus.updateSignAndZeroFlagFrom16BitValue(result);
    if (mA >= value) {
        mCpuStatus.setCarryFlag();
    } else {
        mCpuStatus.clearCarryFlag();
    }
}
void Cpu65816::executeCMP(OpCode &opCode) {
    if (accumulatorIs8BitWide()) {
        execute8BitCMP(opCode);
    } else {
        execute16BitCMP(opCode);
        addToCycles(1);
    }

    switch(opCode.getCode()) {
        case(0xC9):  // CMP Immediate
        {
            if (accumulatorIs16BitWide()) {
                addToProgramAddress(1);
            }
            addToProgramAddressAndCycles(2, 2);
            break;
        }
        case(0xCD):  // CMP Absolute
        {
            addToProgramAddressAndCycles(3, 4);
            break;
        }
        case(0xCF):  // CMP Absolute Long
        {
            addToProgramAddressAndCycles(4, 5);
            break;
        }
        case(0xC5):  // CMP Direct Page
        {
            if (Binary::lower8BitsOf(mD) != 0) {
                addToCycles(1);
            }
            addToProgramAddressAndCycles(2, 3);
            break;
        }
        case(0xD2):  // CMP Direct Page Indirect
        {
            if (Binary::lower8BitsOf(mD) != 0) {
                addToCycles(1);
            }
            addToProgramAddressAndCycles(2, 5);
            break;
        }
        case(0xC7):  // CMP Direct Page Indirect Long
        {
            addToProgramAddressAndCycles(2, 6);
            break;
        }
        case(0xDD):  // CMP Absolute Indexed, X
        {
            if (opCodeAddressingCrossesPageBoundary(opCode)) {
                addToCycles(1);
            }
            addToProgramAddressAndCycles(3, 4);
            break;
        }
        case(0xDF):  // CMP Absolute Long Indexed, X
        {
            addToProgramAddressAndCycles(4, 5);
            break;
        }
        case(0xD9):  // CMP Absolute Indexed, Y
        {
            if (opCodeAddressingCrossesPageBoundary(opCode)) {
                addToCycles(1);
            }
            addToProgramAddressAndCycles(3, 4);
            break;
        }
        case(0xD5):  // CMP Direct Page Indexed, X
        {
            if (Binary::lower8BitsOf(mD) != 0) {
                addToCycles(1);
            }
            addToProgramAddressAndCycles(2, 4);
            break;
        }
        case(0xC1):  // CMP Direct Page Indexed Indirect, X
        {
            if (Binary::lower8BitsOf(mD) != 0) {
                addToCycles(1);
            }
            addToProgramAddressAndCycles(2, 6);
            break;
        }
        case(0xD1):  // CMP Direct Page Indexed Indirect, Y
        {
            if (Binary::lower8BitsOf(mD) != 0) {
                addToCycles(1);
            }
            if (opCodeAddressingCrossesPageBoundary(opCode)) {
                addToCycles(1);
            }
            addToProgramAddressAndCycles(2, 5);
            break;
        }
        case(0xD7):  // CMP Direct Page Indirect Long Indexed, Y
        {
            if (Binary::lower8BitsOf(mD) != 0) {
                addToCycles(1);
            }
            addToProgramAddressAndCycles(2, 6);
            break;
        }
        case(0xC3):  // CMP Stack Relative
        {
            addToProgramAddressAndCycles(2, 4);
            break;
        }
        case(0xD3):  // CMP Stack Relative Indirect Indexed, Y
        {
            addToProgramAddressAndCycles(2, 7);
            break;
        }
        default: {
            LOG_UNEXPECTED_OPCODE(opCode);
        }
    }
}