nesemu/cpu/op.c

#include <stdbool.h>
#include <stdlib.h>
#include <assert.h>

#include "op.h"
#include "cpu.h"
#include "../include/cpu.h"

// Reference: https://www.nesdev.org/wiki/CPU_unofficial_opcodes
// https://www.middle-engine.com/blog/posts/2020/06/23/programming-the-nes-the-6502-in-detail

#define IS_OP_CODE_MODE(op, op_code, addr_mode) \
    case op_code: \
        op_ ## op(ADDR_MODE_ ## addr_mode); \
        break;

#define IS_OP_CODE(op, op_code) \
    IS_OP_CODE_MODE(op, op_code, IMPLICIT)

#define IS_ALU_OP_CODE_(op, offset, addr_mode) \
    IS_OP_CODE_MODE(op, OP_CODE_BASE_ ## op + offset, addr_mode)

#define IS_ALU_OP_CODE(op) \
    IS_ALU_OP_CODE_(op, 0x01, INDIRECT_X) \
    IS_ALU_OP_CODE_(op, 0x05, ZERO_PAGE) \
    IS_ALU_OP_CODE_(op, 0x09, IMMEDIATE) \
    IS_ALU_OP_CODE_(op, 0x0d, ABSOLUTE) \
    IS_ALU_OP_CODE_(op, 0x11, INDIRECT_Y) \
    IS_ALU_OP_CODE_(op, 0x15, ZERO_PAGE_INDEXED_X) \
    IS_ALU_OP_CODE_(op, 0x19, ABSOLUTE_INDEXED_Y) \
    IS_ALU_OP_CODE_(op, 0x1d, ABSOLUTE_INDEXED_X)

#define IS_ALU_OP_CODE_NO_IMMEDIATE(op) \
    IS_ALU_OP_CODE_(op, 0x01, INDIRECT_X) \
    IS_ALU_OP_CODE_(op, 0x05, ZERO_PAGE) \
    IS_ALU_OP_CODE_(op, 0x0d, ABSOLUTE) \
    IS_ALU_OP_CODE_(op, 0x11, INDIRECT_Y) \
    IS_ALU_OP_CODE_(op, 0x15, ZERO_PAGE_INDEXED_X) \
    IS_ALU_OP_CODE_(op, 0x19, ABSOLUTE_INDEXED_Y) \
    IS_ALU_OP_CODE_(op, 0x1d, ABSOLUTE_INDEXED_X)

#define IS_RMW_OP_CODE_(op, line, offset, addr_mode) \
    IS_OP_CODE_MODE(op, OP_CODE_BASE_ ## line + offset, addr_mode)

#define IS_RMW_OP_CODE(op, line) \
    IS_RMW_OP_CODE_(op, line, 0x06, ZERO_PAGE) \
    IS_RMW_OP_CODE_(op, line, 0x0a, IMPLICIT) \
    IS_RMW_OP_CODE_(op, line, 0x0e, ABSOLUTE) \
    IS_RMW_OP_CODE_(op, line, 0x16, ZERO_PAGE_INDEXED_X) \
    IS_RMW_OP_CODE_(op, line, 0x1e, ABSOLUTE_INDEXED_X)

#define IS_UNOFFICIAL_OP_CODE_(op, line, offset, addr_mode) \
    IS_OP_CODE_MODE(op, OP_CODE_BASE_ ## line + offset, addr_mode)

#define IS_UNOFFICIAL_OP_CODE(op, line) \
    IS_UNOFFICIAL_OP_CODE_(op, line, 0x03, INDIRECT_X) \
    IS_UNOFFICIAL_OP_CODE_(op, line, 0x07, ZERO_PAGE) \
    IS_UNOFFICIAL_OP_CODE_(op, line, 0x0f, ABSOLUTE) \
    IS_UNOFFICIAL_OP_CODE_(op, line, 0x13, INDIRECT_Y) \
    IS_UNOFFICIAL_OP_CODE_(op, line, 0x17, ZERO_PAGE_INDEXED_X) \
    IS_UNOFFICIAL_OP_CODE_(op, line, 0x1b, ABSOLUTE_INDEXED_Y) \
    IS_UNOFFICIAL_OP_CODE_(op, line, 0x1f, ABSOLUTE_INDEXED_X)

address decode_operand_addr(AddressingMode addr_mode, bool *page_crossing) {
    CpuRegisters *registers = cpu_get_registers();

    if (addr_mode == ADDR_MODE_ZERO_PAGE) {
        return cpu_get_next_byte();
    } else if (addr_mode == ADDR_MODE_ZERO_PAGE_INDEXED_X) {
        return (cpu_get_next_byte() + registers->x) & 0xff;
    } else if (addr_mode == ADDR_MODE_ZERO_PAGE_INDEXED_Y) {
        return (cpu_get_next_byte() + registers->y) & 0xff;
    } else if (addr_mode == ADDR_MODE_ABSOLUTE || addr_mode == ADDR_MODE_ABSOLUTE_JUMP) {
        return cpu_get_next_word();
    } else if (addr_mode == ADDR_MODE_ABSOLUTE_INDEXED_X) {
        word addr = cpu_get_next_word();
        word new_addr = addr + registers->x;

        *page_crossing = (addr & 0xff00) != (new_addr & 0xff00);

        return new_addr;
    } else if (addr_mode == ADDR_MODE_ABSOLUTE_INDEXED_Y) {
        word addr = cpu_get_next_word();
        word new_addr = addr + registers->y;

        *page_crossing = (addr & 0xff00) != (new_addr & 0xff00);

        return new_addr;
    } else if (addr_mode == ADDR_MODE_INDIRECT_JUMP) {
        word addr = cpu_get_next_word();
        if ((addr & 0xff) == 0xff) {
            // Error in NES CPU for JMP op
            word result = cpu_peek_byte(addr);
            result += cpu_peek_byte(addr & 0xff00) << 8;
            return result;
        }
        return cpu_peek_word(addr);
    } else if (addr_mode == ADDR_MODE_INDIRECT_X) {
        byte addr = cpu_get_next_byte();
        word result = cpu_peek_byte((addr + registers->x) & 0xff);
        result += cpu_peek_byte((addr + registers->x + 1) & 0xff) << 8;
        return result;
    } else if (addr_mode == ADDR_MODE_INDIRECT_Y) {
        byte arg_addr = cpu_get_next_byte();
        word addr = cpu_peek_byte(arg_addr) + (cpu_peek_byte((arg_addr + 1) & 0xff) << 8);
        word new_addr = addr + registers->y;

        *page_crossing = (addr & 0xff00) != (new_addr & 0xff00);

        return new_addr;
    } else {
        assert(false);
    }
}

Operand decode_operand(AddressingMode addr_mode) {
    Operand operand;

    if (addr_mode == ADDR_MODE_ACCUMULATOR) {
        operand.type = OPERAND_TYPE_ACCUMULATOR;
        operand.value = 0;
        operand.is_page_crossing = false;
    } else if (addr_mode == ADDR_MODE_IMMEDIATE) {
        operand.type = OPERAND_TYPE_IMMEDIATE;
        operand.value = cpu_get_next_byte();
        operand.is_page_crossing = false;
    } else {
        operand.type = OPERAND_TYPE_ADDRESS;
        operand.value = decode_operand_addr(addr_mode, &operand.is_page_crossing);
    }

    return operand;
}

byte read_operand(Operand operand) {
    switch (operand.type) {
        case OPERAND_TYPE_ACCUMULATOR:
            return cpu_get_registers()->accumulator;
        case OPERAND_TYPE_IMMEDIATE:
            return (byte) operand.value;
        case OPERAND_TYPE_ADDRESS:
            return cpu_peek_byte(operand.value);
        default:
            assert(false);
    }
}

void write_operand(Operand operand, byte value) {
    switch (operand.type) {
        case OPERAND_TYPE_ACCUMULATOR:
            cpu_get_registers()->accumulator = value;
            break;
        case OPERAND_TYPE_ADDRESS:
            cpu_push_byte(operand.value, value);
            break;
        default:
            assert(false);
    }
}

bool is_sign_overflow(byte val1, byte val2, byte result) {
    return ((val1 & 0x80) == (val2 & 0x80)) &&
           ((val1 & 0x80) != (result & 0x80));
}

byte get_cycle_count(Operand operand, AddressingMode addr_mode) {
    switch (addr_mode) {
        case ADDR_MODE_ACCUMULATOR:
        case ADDR_MODE_IMPLICIT:
            return 2;
        case ADDR_MODE_ZERO_PAGE:
            return 3;
        case ADDR_MODE_ZERO_PAGE_INDEXED_X:
        case ADDR_MODE_ZERO_PAGE_INDEXED_Y:
        case ADDR_MODE_ABSOLUTE:
            return 4;
        case ADDR_MODE_ABSOLUTE_INDEXED_X:
        case ADDR_MODE_ABSOLUTE_INDEXED_Y:
            return operand.is_page_crossing ? 5 : 4;
        case ADDR_MODE_INDIRECT_X:
            return 6;
        case ADDR_MODE_INDIRECT_Y:
            return operand.is_page_crossing ? 6 : 5;
        default:
            assert(false);
    }
}

byte get_shift_cycle_count(AddressingMode addr_mode) {
    switch (addr_mode) {
        case ADDR_MODE_ACCUMULATOR:
            return 2;
        case ADDR_MODE_ZERO_PAGE:
            return 5;
        case ADDR_MODE_ZERO_PAGE_INDEXED_X:
        case ADDR_MODE_ABSOLUTE:
            return 6;
        case ADDR_MODE_ABSOLUTE_INDEXED_X:
            return 7;
        default:
            assert(false);
    }
}

void set_acl_flags(byte result) {
    cpu_set_flag(result == 0, CPU_STATUS_ZERO_MASK);
    cpu_set_flag(result & 0x80, CPU_STATUS_NEGATIVE_MASK);
}

byte get_branch_cycle_count(bool branching, char offset) {
    address target = cpu_get_registers()->program_counter;
    byte cycle_count = 2;

    if (branching) {
        cycle_count += 1;

        if ((target & 0xff00) != ((target - offset) & 0xff00)) {
            cycle_count += 2;
        }
    }

    return cycle_count;
}

void op_branch(bool branching) {
    char offset = (char) cpu_get_next_byte();

    if (branching) {
        address counter = cpu_get_registers()->program_counter;
        address target = counter + offset;
        cpu_get_registers()->program_counter = target;
    }

    cpu_add_cycles(get_branch_cycle_count(branching, offset));
}

void add_with_carry(byte value) {
    byte acc = cpu_get_registers()->accumulator;

    byte addition = acc + value;
    bool overflow = false;

    // Check for overflow
    if (addition < acc) {
        overflow = true;
    }

    // Add carry flag and check for overflow again
    byte result = addition + cpu_get_flag(CPU_STATUS_CARRY_MASK);
    if (result < addition) {
        overflow = true;
    }

    cpu_get_registers()->accumulator = acc;

    cpu_set_flag(overflow, CPU_STATUS_CARRY_MASK);
    cpu_set_flag(is_sign_overflow(acc, value, result));

    set_acl_flags(result);
}

void op_ADC(AddressingMode addr_mode) {
    Operand operand = decode_operand(addr_mode);

    byte value = read_operand(operand);
    add_with_carry(value);

    cpu_add_cycles(get_cycle_count(operand, addr_mode));
}

void op_AHX(AddressingMode addr_mode) {
    assert(false);
}

void op_ALR(AddressingMode addr_mode) {
    assert(false);
}

void op_ANC(AddressingMode addr_mode) {
    assert(false);
}

void op_AND(AddressingMode addr_mode) {
    Operand operand = decode_operand(addr_mode);
    byte value = read_operand(operand);
    byte acc = cpu_get_registers()->accumulator;

    byte result = acc & value;
    cpu_get_registers()->accumulator = result;

    set_acl_flags(result);
    cpu_add_cycles(get_cycle_count(operand, addr_mode));
}

void op_ARR(AddressingMode addr_mode) {
    assert(false);
}

void op_ASL(AddressingMode addr_mode) {
    Operand operand = decode_operand(addr_mode);
    byte value = read_operand(operand);

    byte result = value << 1;
    write_operand(operand, result);

    cpu_set_flag(value & 0x80, CPU_STATUS_CARRY_MASK);
    set_acl_flags(result);
    cpu_add_cycles(get_shift_cycle_count(addr_mode));
}

void op_AXS(AddressingMode addr_mode) {
    assert(false);
}

void op_BCC(AddressingMode addr_mode) {
    op_branch(!cpu_get_flag(CPU_STATUS_CARRY_MASK));
}

void op_BCS(AddressingMode addr_mode) {
    op_branch(cpu_get_flag(CPU_STATUS_CARRY_MASK));
}

void op_BEQ(AddressingMode addr_mode) {
    op_branch(cpu_get_flag(CPU_STATUS_ZERO_MASK));
}

void op_BIT(AddressingMode addr_mode) {
    Operand operand = decode_operand(addr_mode);
    byte value = read_operand(operand);
    byte acc = cpu_get_registers()->accumulator;

    byte result = value & acc;

    cpu_set_flag(result == 0, CPU_STATUS_ZERO_MASK);
    cpu_set_flag(result & 0x40, CPU_STATUS_OVERFLOW_MASK);
    cpu_set_flag(result & 0x80, CPU_STATUS_NEGATIVE_MASK);
}

void op_BMI(AddressingMode addr_mode) {
    op_branch(cpu_get_flag(CPU_STATUS_NEGATIVE_MASK));
}

void op_BNE(AddressingMode addr_mode) {
    op_branch(!cpu_get_flag(CPU_STATUS_ZERO_MASK));
}

void op_BPL(AddressingMode addr_mode) {
    op_branch(!cpu_get_flag(CPU_STATUS_NEGATIVE_MASK));
}

// Stops program execution, useful for debugging
void op_BRK(AddressingMode addr_mode) {
    cpu_stack_push_context();

    // TODO Load IRQ interrupt vector in PC at $FFFE/F

    cpu_set_flag(true, CPU_STATUS_B_MASK);
    cpu_add_cycles(7);
}

void op_BVC(AddressingMode addr_mode) {
    op_branch(!cpu_get_flag(CPU_STATUS_OVERFLOW_MASK));
}

void op_BVS(AddressingMode addr_mode) {
    op_branch(cpu_get_flag(CPU_STATUS_OVERFLOW_MASK));
}

void op_CLC(AddressingMode addr_mode) {
    cpu_set_flag(false, CPU_STATUS_CARRY_MASK);
    cpu_add_cycles(2);
}

void op_CLD(AddressingMode addr_mode) {
    cpu_set_flag(false, CPU_STATUS_DECIMAL_MASK);
    cpu_add_cycles(2);
}

void op_CLI(AddressingMode addr_mode) {
    cpu_set_flag(false, CPU_STATUS_INTERRUPT_DISABLE_MASK);
    cpu_add_cycles(2);
}

void op_CLV(AddressingMode addr_mode) {
    cpu_set_flag(false, CPU_STATUS_OVERFLOW_MASK);
    cpu_add_cycles(2);
}

void op_CMP(AddressingMode addr_mode) {
    Operand operand = decode_operand(addr_mode);
    byte value = read_operand(operand);
    byte acc = cpu_get_registers()->accumulator;

    byte result = acc - value;

    cpu_set_flag(acc >= value, CPU_STATUS_CARRY_MASK);
    cpu_set_flag(result == 0, CPU_STATUS_ZERO_MASK);
    cpu_set_flag(result & 0x80, CPU_STATUS_NEGATIVE_MASK);

    cpu_add_cycles(get_cycle_count(operand, addr_mode));
}

void op_CPX(AddressingMode addr_mode) {
    Operand operand = decode_operand(addr_mode);
    byte value = read_operand(operand);
    byte x = cpu_get_registers()->x;

    byte result = x - value;

    cpu_set_flag(x >= value, CPU_STATUS_CARRY_MASK);
    cpu_set_flag(result == 0, CPU_STATUS_ZERO_MASK);
    cpu_set_flag(result & 0x80, CPU_STATUS_NEGATIVE_MASK);

    cpu_add_cycles(get_cycle_count(operand, addr_mode));
}

void op_CPY(AddressingMode addr_mode) {
    Operand operand = decode_operand(addr_mode);
    byte value = read_operand(operand);
    byte y = cpu_get_registers()->y;

    byte result = y - value;

    cpu_set_flag(y >= value, CPU_STATUS_CARRY_MASK);
    cpu_set_flag(result == 0, CPU_STATUS_ZERO_MASK);
    cpu_set_flag(result & 0x80, CPU_STATUS_NEGATIVE_MASK);

    cpu_add_cycles(get_cycle_count(operand, addr_mode));
}

void op_DCP(AddressingMode addr_mode) {
    assert(false);
}

void op_DEC(AddressingMode addr_mode) {
    Operand operand = decode_operand(addr_mode);
    byte value = read_operand(operand);

    byte result = value - 1;

    set_acl_flags(result);
    write_operand(operand, result);
    cpu_add_cycles(get_cycle_count(operand, addr_mode));
}

void op_DEX(AddressingMode addr_mode) {
    byte x = cpu_get_registers()->x;

    byte result = x - 1;
    cpu_get_registers()->x = result;

    set_acl_flags(result);
    cpu_add_cycles(2);
}

void op_DEY(AddressingMode addr_mode) {
    byte y = cpu_get_registers()->y;

    byte result = y - 1;
    cpu_get_registers()->y = result;

    set_acl_flags(result);
    cpu_add_cycles(2);
}

void op_EOR(AddressingMode addr_mode) {
    Operand operand = decode_operand(addr_mode);
    byte value = read_operand(operand);
    byte acc = cpu_get_registers()->accumulator;

    acc ^= value;
    cpu_get_registers()->accumulator = acc;

    set_acl_flags(acc);
    cpu_add_cycles(get_cycle_count(operand, addr_mode));
}

void op_INC(AddressingMode addr_mode) {
    Operand operand = decode_operand(addr_mode);
    byte value = read_operand(operand);

    value += 1;
    write_operand(operand, value);

    set_acl_flags(value);
    cpu_add_cycles(get_shift_cycle_count(addr_mode));
}

void op_INX(AddressingMode addr_mode) {
    byte x = cpu_get_registers()->x;

    x += 1;
    cpu_get_registers()->x = x;

    set_acl_flags(x);
    cpu_add_cycles(2);
}

void op_INY(AddressingMode addr_mode) {
    byte y = cpu_get_registers()->y;

    y += 1;
    cpu_get_registers()->y = y;

    set_acl_flags(y);
    cpu_add_cycles(2);
}

void op_ISC(AddressingMode addr_mode) {
    assert(false);
}

void op_JMP(AddressingMode addr_mode) {
    Operand operand = decode_operand(addr_mode);
    byte addr = read_operand(operand);

    cpu_get_registers()->program_counter = addr;

    // TODO WN: Handle CPU bug?
    // > An original 6502 has does not correctly fetch the target address if the indirect vector falls on a page boundary (e.g. $xxFF where xx is any value from $00 to $FF).
    // > In this case fetches the LSB from $xxFF as expected but takes the MSB from $xx00.
    // > This is fixed in some later chips like the 65SC02 so for compatibility always ensure the indirect vector is not at the end of the page.
}

void op_JSR(AddressingMode addr_mode) {
    // Push the program counter on the stack
    address program_counter = cpu_get_registers()->program_counter - 1;
    cpu_stack_push(program_counter >> 8);
    cpu_stack_push(program_counter & 0xff);

    // Updates the program counter to the address in the operand
    address addr = decode_operand_addr(addr_mode, NULL);
    cpu_get_registers()->program_counter = addr;

    cpu_add_cycles(6);
}

void op_LAX(AddressingMode addr_mode) {
    assert(false);
}

void op_LDA(AddressingMode addr_mode) {
    Operand operand = decode_operand(addr_mode);
    byte value = read_operand(operand);

    cpu_get_registers()->accumulator = value;

    set_acl_flags(value);
    cpu_add_cycles(get_cycle_count(operand, addr_mode));
}

void op_LDX(AddressingMode addr_mode) {
    Operand operand = decode_operand(addr_mode);
    byte value = read_operand(operand);

    cpu_get_registers()->x = value;

    set_acl_flags(value);
    cpu_add_cycles(get_cycle_count(operand, addr_mode));
}

void op_LDY(AddressingMode addr_mode) {
    Operand operand = decode_operand(addr_mode);
    byte value = read_operand(operand);

    cpu_get_registers()->y = value;

    set_acl_flags(value);
    cpu_add_cycles(get_cycle_count(operand, addr_mode));
}

void op_LSR(AddressingMode addr_mode) {
    Operand operand = decode_operand(addr_mode);
    byte value = read_operand(operand);

    // Put bit 0 in the carry flag
    cpu_set_flag(value & 0x01, CPU_STATUS_CARRY_MASK);

    value >>= 1;
    write_operand(operand, value);

    set_acl_flags(value);
    cpu_add_cycles(get_shift_cycle_count(addr_mode));
}

void op_NOP(AddressingMode addr_mode) {
    cpu_add_cycles(2);
}

void op_ORA(AddressingMode addr_mode) {
    Operand operand = decode_operand(addr_mode);
    byte value = read_operand(operand);
    byte acc = cpu_get_registers()->accumulator;

    acc |= value;
    cpu_get_registers()->accumulator = acc;

    set_acl_flags(acc);
    cpu_add_cycles(get_cycle_count(operand, addr_mode));
}

void op_PHA(AddressingMode addr_mode) {
    byte acc = cpu_get_registers()->accumulator;
    cpu_stack_push(acc);

    cpu_add_cycles(3);
}

void op_PHP(AddressingMode addr_mode) {
    byte status = cpu_get_registers()->status;
    cpu_stack_push(status);

    cpu_add_cycles(3);
}

void op_PLA(AddressingMode addr_mode) {
    byte value = cpu_stack_pop();
    cpu_get_registers()->accumulator = value;

    cpu_add_cycles(4);
}

void op_PLP(AddressingMode addr_mode) {
    byte value = cpu_stack_pop();
    cpu_get_registers()->status = value;

    cpu_add_cycles(4);
}

void op_RLA(AddressingMode addr_mode) {
    assert(false);
}

void op_ROL(AddressingMode addr_mode) {
    Operand operand = decode_operand(addr_mode);
    byte value = read_operand(operand);
    byte carry = cpu_get_flag(CPU_STATUS_CARRY_MASK);

    cpu_set_flag(value & 0x80, CPU_STATUS_CARRY_MASK);
    value = (value << 1) | carry;
    write_operand(operand, value);

    set_acl_flags(value);
    cpu_add_cycles(get_shift_cycle_count(addr_mode));
}

void op_ROR(AddressingMode addr_mode) {
    Operand operand = decode_operand(addr_mode);
    byte value = read_operand(operand);
    byte carry = cpu_get_flag(CPU_STATUS_CARRY_MASK);

    cpu_set_flag(value & 0x01, CPU_STATUS_CARRY_MASK);
    value = (value >> 1) | (carry << 7);
    write_operand(operand, value);

    set_acl_flags(value);
    cpu_add_cycles(get_shift_cycle_count(addr_mode));
}

void op_RRA(AddressingMode addr_mode) {
    assert(false);
}

void op_RTI(AddressingMode addr_mode) {
    cpu_stack_pop_context();
    cpu_add_cycles(6);
}

void op_RTS(AddressingMode addr_mode) {
    byte lo = cpu_stack_pop();
    address pc = cpu_stack_pop() << 8;
    pc += lo;

    cpu_get_registers()->program_counter = pc - 1;
    cpu_add_cycles(6);
}

void op_SAX(AddressingMode addr_mode) {
    assert(false);
}

void op_SBC(AddressingMode addr_mode) {
    Operand operand = decode_operand(addr_mode);
    byte value = read_operand(operand);

    add_with_carry(~value);

    cpu_add_cycles(get_cycle_count(operand, addr_mode));
}

void op_SEC(AddressingMode addr_mode) {
    cpu_set_flag(1, CPU_STATUS_CARRY_MASK);
    cpu_add_cycles(2);
}

void op_SED(AddressingMode addr_mode) {
    cpu_set_flag(1, CPU_STATUS_DECIMAL_MASK);
    cpu_add_cycles(2);
}

void op_SEI(AddressingMode addr_mode) {
    cpu_set_flag(1, CPU_STATUS_INTERRUPT_DISABLE_MASK);
    cpu_add_cycles(2);
}

void op_SHX(AddressingMode addr_mode) {
    assert(false);
}

void op_SHY(AddressingMode addr_mode) {
    assert(false);
}

void op_SLO(AddressingMode addr_mode) {
    assert(false);
}

void op_SRE(AddressingMode addr_mode) {
    assert(false);
}

void op_STA(AddressingMode addr_mode) {
    Operand operand = decode_operand(addr_mode);
    byte acc = cpu_get_registers()->accumulator;
    assert(operand.type == OPERAND_TYPE_ADDRESS);

    cpu_push_byte(acc, operand.value);

    operand.is_page_crossing = true;
    cpu_add_cycles(get_cycle_count(operand, addr_mode));
}

void op_STP(AddressingMode addr_mode) {
    assert(false);
}

void op_STX(AddressingMode addr_mode) {
    Operand operand = decode_operand(addr_mode);
    byte x = cpu_get_registers()->x;
    assert(operand.type == OPERAND_TYPE_ADDRESS);

    cpu_push_byte(x, operand.value);

    cpu_add_cycles(get_cycle_count(operand, addr_mode));
}

void op_STY(AddressingMode addr_mode) {
    Operand operand = decode_operand(addr_mode);
    byte y = cpu_get_registers()->y;
    assert(operand.type == OPERAND_TYPE_ADDRESS);

    cpu_push_byte(y, operand.value);

    cpu_add_cycles(get_cycle_count(operand, addr_mode));
}

void op_TAS(AddressingMode addr_mode) {
    assert(false);
}

void op_TAX(AddressingMode addr_mode) {
    byte acc = cpu_get_registers()->accumulator;
    cpu_get_registers()->x = acc;

    set_acl_flags(acc);
    cpu_add_cycles(2);
}

void op_TAY(AddressingMode addr_mode) {
    byte acc = cpu_get_registers()->accumulator;
    cpu_get_registers()->y = acc;

    set_acl_flags(acc);
    cpu_add_cycles(2);
}

void op_TSX(AddressingMode addr_mode) {
    byte value = cpu_stack_pop();
    cpu_get_registers()->x = value;

    set_acl_flags(value);
    cpu_add_cycles(2);
}

void op_TXA(AddressingMode addr_mode) {
    byte x = cpu_get_registers()->x;
    cpu_get_registers()->accumulator = x;

    set_acl_flags(x);
    cpu_add_cycles(2);
}

void op_TXS(AddressingMode addr_mode) {
    byte x = cpu_get_registers()->x;
    cpu_stack_push(x);

    cpu_add_cycles(2);
}

void op_TYA(AddressingMode addr_mode) {
    byte y = cpu_get_registers()->y;
    cpu_get_registers()->accumulator = y;

    set_acl_flags(y);
    cpu_add_cycles(2);
}

void op_XAA(AddressingMode addr_mode) {
    assert(false);
}

void process_op_code(int op) {
    switch (op) {
        // CTRL
        IS_OP_CODE(BRK, 0x00)
        IS_OP_CODE(PHP, 0x08)
        IS_OP_CODE(CLC, 0x18)
        IS_OP_CODE(PLP, 0x28)
        IS_OP_CODE(SEC, 0x38)
        IS_OP_CODE(RTI, 0x40)
        IS_OP_CODE(PHA, 0x48)
        IS_OP_CODE(CLI, 0x58)
        IS_OP_CODE(RTS, 0x60)
        IS_OP_CODE(PLA, 0x68)
        IS_OP_CODE(SEI, 0x78)
        IS_OP_CODE(DEY, 0x88)
        IS_OP_CODE(TYA, 0x98)
        IS_OP_CODE(TAY, 0xa8)
        IS_OP_CODE(CLV, 0xb8)
        IS_OP_CODE(INY, 0xc8)
        IS_OP_CODE(CLD, 0xd8)
        IS_OP_CODE(INX, 0xe8)
        IS_OP_CODE(SED, 0xf8)

        IS_OP_CODE_MODE(JSR, 0x20, ABSOLUTE)
        IS_OP_CODE_MODE(BIT, 0x24, ZERO_PAGE)
        IS_OP_CODE_MODE(BIT, 0x2c, ABSOLUTE)
        IS_OP_CODE_MODE(JMP, 0x4c, ABSOLUTE)
        IS_OP_CODE_MODE(JMP, 0x6c, ABSOLUTE_JUMP)
        IS_OP_CODE_MODE(STY, 0x84, ZERO_PAGE)
        IS_OP_CODE_MODE(STY, 0x8c, ABSOLUTE)
        IS_OP_CODE_MODE(STY, 0x94, ZERO_PAGE_INDEXED_X)
        IS_OP_CODE_MODE(SHY, 0x9c, ABSOLUTE_INDEXED_X)
        IS_OP_CODE_MODE(LDY, 0xa0, IMMEDIATE)
        IS_OP_CODE_MODE(LDY, 0xa4, ZERO_PAGE)
        IS_OP_CODE_MODE(LDY, 0xac, ABSOLUTE)
        IS_OP_CODE_MODE(LDY, 0xb4, ZERO_PAGE_INDEXED_X)
        IS_OP_CODE_MODE(LDY, 0xbc, ABSOLUTE_INDEXED_X)
        IS_OP_CODE_MODE(CPY, 0xc0, IMMEDIATE)
        IS_OP_CODE_MODE(CPY, 0xc4, ZERO_PAGE)
        IS_OP_CODE_MODE(CPY, 0xcc, ABSOLUTE)
        IS_OP_CODE_MODE(CPX, 0xe0, IMMEDIATE)
        IS_OP_CODE_MODE(CPX, 0xe4, ZERO_PAGE)
        IS_OP_CODE_MODE(CPX, 0xec, ABSOLUTE)

        IS_OP_CODE_MODE(BPL, 0x10, RELATIVE)
        IS_OP_CODE_MODE(BMI, 0x30, RELATIVE)
        IS_OP_CODE_MODE(BVC, 0x50, RELATIVE)
        IS_OP_CODE_MODE(BVS, 0x70, RELATIVE)
        IS_OP_CODE_MODE(BCC, 0x90, RELATIVE)
        IS_OP_CODE_MODE(BCS, 0xb0, RELATIVE)
        IS_OP_CODE_MODE(BNE, 0xd0, RELATIVE)
        IS_OP_CODE_MODE(BEQ, 0xf0, RELATIVE)

        IS_OP_CODE_MODE(NOP, 0x04, ZERO_PAGE)
        IS_OP_CODE_MODE(NOP, 0x0c, ABSOLUTE)
        IS_OP_CODE_MODE(NOP, 0x14, ZERO_PAGE_INDEXED_X)
        IS_OP_CODE_MODE(NOP, 0x1c, ABSOLUTE_INDEXED_X)
        IS_OP_CODE_MODE(NOP, 0x34, ZERO_PAGE_INDEXED_X)
        IS_OP_CODE_MODE(NOP, 0x3c, ABSOLUTE_INDEXED_X)
        IS_OP_CODE_MODE(NOP, 0x44, ZERO_PAGE)
        IS_OP_CODE_MODE(NOP, 0x54, ZERO_PAGE_INDEXED_X)
        IS_OP_CODE_MODE(NOP, 0x5c, ABSOLUTE_INDEXED_X)
        IS_OP_CODE_MODE(NOP, 0x64, ZERO_PAGE)
        IS_OP_CODE_MODE(NOP, 0x74, ZERO_PAGE_INDEXED_X)
        IS_OP_CODE_MODE(NOP, 0x7c, ZERO_PAGE_INDEXED_X)
        IS_OP_CODE_MODE(NOP, 0x80, IMMEDIATE)
        IS_OP_CODE_MODE(NOP, 0xd4, ZERO_PAGE_INDEXED_X)
        IS_OP_CODE_MODE(NOP, 0xdc, ABSOLUTE_INDEXED_X)
        IS_OP_CODE_MODE(NOP, 0xf4, ZERO_PAGE_INDEXED_X)
        IS_OP_CODE_MODE(NOP, 0xfc, ABSOLUTE_INDEXED_X)

        // ALU
        IS_ALU_OP_CODE(ORA)
        IS_ALU_OP_CODE(AND)
        IS_ALU_OP_CODE(EOR)
        IS_ALU_OP_CODE(ADC)
        IS_ALU_OP_CODE_NO_IMMEDIATE(STA)
        IS_ALU_OP_CODE(LDA)
        IS_ALU_OP_CODE(CMP)
        IS_ALU_OP_CODE(SBC)

        // RMW
        IS_RMW_OP_CODE(ASL, ORA)
        IS_RMW_OP_CODE(ROL, AND)
        IS_RMW_OP_CODE(LSR, EOR)
        IS_RMW_OP_CODE(ROR, ADC)

        IS_OP_CODE(STP, 0x02)
        IS_OP_CODE(STP, 0x12)
        IS_OP_CODE(NOP, 0x1a)
        IS_OP_CODE(STP, 0x22)
        IS_OP_CODE(STP, 0x32)
        IS_OP_CODE(NOP, 0x3a)
        IS_OP_CODE(STP, 0x42)
        IS_OP_CODE(STP, 0x52)
        IS_OP_CODE(NOP, 0x5a)
        IS_OP_CODE(STP, 0x62)
        IS_OP_CODE(STP, 0x72)
        IS_OP_CODE(NOP, 0x7a)

        IS_OP_CODE_MODE(NOP, 0x82, IMMEDIATE)
        IS_OP_CODE_MODE(STX, 0x86, ZERO_PAGE)
        IS_OP_CODE(TXA, 0x8a)
        IS_OP_CODE_MODE(STX, 0x8e, ABSOLUTE)
        IS_OP_CODE(STP, 0x92)
        IS_OP_CODE_MODE(STX, 0x96, ZERO_PAGE_INDEXED_Y)
        IS_OP_CODE(TSX, 0x9a)
        IS_OP_CODE_MODE(SHX, 0x9e, ABSOLUTE_INDEXED_Y)

        IS_OP_CODE_MODE(LDX, 0xa2, IMMEDIATE)
        IS_OP_CODE_MODE(LDX, 0xa6, ZERO_PAGE)
        IS_OP_CODE(TAX, 0xaa)
        IS_OP_CODE_MODE(LDX, 0xae, ABSOLUTE)
        IS_OP_CODE(STP, 0xb2)
        IS_OP_CODE_MODE(LDX, 0xb6, ZERO_PAGE_INDEXED_Y)
        IS_OP_CODE(TSX, 0xba)
        IS_OP_CODE_MODE(LDX, 0xbe, ABSOLUTE_INDEXED_Y)

        IS_OP_CODE_MODE(NOP, 0xc2, IMMEDIATE)
        IS_OP_CODE_MODE(DEC, 0xc6, ZERO_PAGE)
        IS_OP_CODE(DEX, 0xca)
        IS_OP_CODE_MODE(DEC, 0xce, ABSOLUTE)
        IS_OP_CODE(STP, 0xd2)
        IS_OP_CODE_MODE(DEC, 0xd6, ZERO_PAGE_INDEXED_Y)
        IS_OP_CODE(NOP, 0xda)
        IS_OP_CODE_MODE(DEC, 0xde, ABSOLUTE_INDEXED_Y)

        IS_OP_CODE_MODE(NOP, 0xe2, IMMEDIATE)
        IS_OP_CODE_MODE(INC, 0xe6, ZERO_PAGE)
        IS_OP_CODE(NOP, 0xea)   // The official NOP
        IS_OP_CODE_MODE(INC, 0xee, ABSOLUTE)
        IS_OP_CODE(STP, 0xf2)
        IS_OP_CODE_MODE(INC, 0xf6, ZERO_PAGE_INDEXED_Y)
        IS_OP_CODE(NOP, 0xfa)
        IS_OP_CODE_MODE(INC, 0xfe, ABSOLUTE_INDEXED_X)

        // Unofficial
        IS_UNOFFICIAL_OP_CODE(SLO, ORA)
        IS_UNOFFICIAL_OP_CODE(RLA, AND)
        IS_UNOFFICIAL_OP_CODE(SRE, EOR)
        IS_UNOFFICIAL_OP_CODE(RRA, ADC)
        IS_UNOFFICIAL_OP_CODE(DCP, CMP)
        IS_UNOFFICIAL_OP_CODE(ISC, SBC)

        IS_OP_CODE_MODE(ANC, 0x0b, IMMEDIATE)
        IS_OP_CODE_MODE(ANC, 0x2b, IMMEDIATE)
        IS_OP_CODE_MODE(ALR, 0x4b, IMMEDIATE)
        IS_OP_CODE_MODE(ARR, 0x6b, IMMEDIATE)
        IS_OP_CODE_MODE(AXS, 0xcb, IMMEDIATE)
        IS_OP_CODE_MODE(SBC, 0xeb, IMMEDIATE)

        IS_OP_CODE_MODE(SAX, 0x83, INDIRECT_X)
        IS_OP_CODE_MODE(SAX, 0x87, ZERO_PAGE)
        IS_OP_CODE_MODE(XAA, 0x8b, IMMEDIATE)
        IS_OP_CODE_MODE(SAX, 0x8f, ABSOLUTE)
        IS_OP_CODE_MODE(AHX, 0x93, INDIRECT_Y)
        IS_OP_CODE_MODE(SAX, 0x97, ZERO_PAGE_INDEXED_Y)
        IS_OP_CODE_MODE(TAS, 0x9b, ABSOLUTE_INDEXED_Y)
        IS_OP_CODE_MODE(AHX, 0x9f, ABSOLUTE_INDEXED_Y)

        IS_OP_CODE_MODE(LAX, 0xa3, INDIRECT_X)
        IS_OP_CODE_MODE(LAX, 0xa7, ZERO_PAGE)
        IS_OP_CODE_MODE(LAX, 0xab, IMMEDIATE)
        IS_OP_CODE_MODE(LAX, 0xaf, ABSOLUTE)
        IS_OP_CODE_MODE(LAX, 0xb3, INDIRECT_Y)
        IS_OP_CODE_MODE(LAX, 0xb7, ZERO_PAGE_INDEXED_Y)
        IS_OP_CODE_MODE(LAX, 0xbb, ABSOLUTE_INDEXED_Y)
        IS_OP_CODE_MODE(LAX, 0xbf, ABSOLUTE_INDEXED_Y)
    }
}