nesemu/cpu/op.c

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

#include "op.h"
#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(system, 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, ACCUMULATOR) \
    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)

char *addr_mode_name(AddressingMode addr_mode) {
    switch (addr_mode) {
        case ADDR_MODE_ABSOLUTE:
            return "Absolute";
        case ADDR_MODE_ABSOLUTE_JUMP:
            return "Absolute Jump";
        case ADDR_MODE_ABSOLUTE_INDEXED_X:
            return "Absolute Indexed X";
        case ADDR_MODE_ABSOLUTE_INDEXED_Y:
            return "Absolute Indexed Y";
        case ADDR_MODE_ACCUMULATOR:
            return "Accumulator";
        case ADDR_MODE_IMMEDIATE:
            return "Immediate";
        case ADDR_MODE_IMPLICIT:
            return "Implicit";
        case ADDR_MODE_INDIRECT_X:
            return "Indirect X";
        case ADDR_MODE_INDIRECT_JUMP:
            return "Indirect Jump";
        case ADDR_MODE_INDIRECT_Y:
            return "Indirect Y";
        case ADDR_MODE_RELATIVE:
            return "Relative";
        case ADDR_MODE_ZERO_PAGE:
            return "Zero Page";
        case ADDR_MODE_ZERO_PAGE_INDEXED_X:
            return "Zero Page X";
        case ADDR_MODE_ZERO_PAGE_INDEXED_Y:
            return "Zero Page Y";
    }
}

address decode_operand_addr(System *system, AddressingMode addr_mode, bool *page_crossing) {
    CPU registers = system->cpu;
    address operand_addr;

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

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

        operand_addr = new_addr;
    } else if (addr_mode == ADDR_MODE_ABSOLUTE_INDEXED_Y) {
        word addr = cpu_get_next_word(system);
        word new_addr = addr + registers.y;

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

        operand_addr = new_addr;
    } else if (addr_mode == ADDR_MODE_INDIRECT_JUMP) {
        word addr = cpu_get_next_word(system);
        if ((addr & 0xff) == 0xff) {
            // Error in NES CPU for JMP op
            word result = mem_get_byte(system, addr);
            result += mem_get_byte(system, addr & 0xff00) << 8;
            operand_addr = result;
        } else {
            operand_addr = mem_get_word(system, addr);
        }
    } else if (addr_mode == ADDR_MODE_INDIRECT_X) {
        byte arg_addr = cpu_get_next_byte(system);

        word addr = mem_get_byte(system, (arg_addr + system->cpu.x) & 0xff);
        addr += mem_get_byte(system, (arg_addr + system->cpu.x + 1) & 0xff) << 8;
        operand_addr = addr;
    } else if (addr_mode == ADDR_MODE_INDIRECT_Y) {
        byte arg_addr = cpu_get_next_byte(system);
        word addr = mem_get_byte(system, arg_addr) + (mem_get_byte(system, (arg_addr + 1) & 0xff) << 8);
        word new_addr = addr + registers.y;

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

        operand_addr = new_addr;
    } else {
        assert(false);
    }

    log_trace("Operand address: %#02x, Addressing mode: %s", operand_addr, addr_mode_name(addr_mode));
    return operand_addr;
}

Operand decode_operand(System *system, 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(system);
        operand.is_page_crossing = false;
    } else {
        operand.type = OPERAND_TYPE_ADDRESS;
        operand.value = decode_operand_addr(system, addr_mode, &operand.is_page_crossing);
    }

    log_trace("Operand type: %s, value: %#02x", operand_name(&operand), operand.value);
    return operand;
}

byte read_operand(System *system, Operand operand) {
    switch (operand.type) {
        case OPERAND_TYPE_ACCUMULATOR:
            return system->cpu.accumulator;
        case OPERAND_TYPE_IMMEDIATE:
            return (byte) operand.value;
        case OPERAND_TYPE_ADDRESS:
            return mem_get_byte(system, operand.value);
        default:
            assert(false);
    }
}

void write_operand(System *system, Operand operand, byte value) {
    switch (operand.type) {
        case OPERAND_TYPE_ACCUMULATOR:
            system->cpu.accumulator = value;
            break;
        case OPERAND_TYPE_ADDRESS:
            mem_set_byte(system, 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_IMMEDIATE:
            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:
        case ADDR_MODE_ABSOLUTE_INDEXED_Y:
            return 7;
        case ADDR_MODE_INDIRECT_X:
        case ADDR_MODE_INDIRECT_Y:
            return 8;
        default:
            assert(false);
    }
}

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

byte get_branch_cycle_count(System *system, bool branching, char offset) {
    address target = system->cpu.program_counter;
    byte cycle_count = 2;

    if (branching) {
        cycle_count += 1;

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

    return cycle_count;
}

__attribute__((unused))
void op_branch(System *system, bool branching) {
    char offset = (char) cpu_get_next_byte(system);

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

    cpu_add_cycles(system, get_branch_cycle_count(system, branching, offset));
}

void add_with_carry(System *system, byte value) {
    byte acc = system->cpu.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(system, CPU_STATUS_CARRY_MASK);
    if (result < addition) {
        overflow = true;
    }

    system->cpu.accumulator = result;

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

    set_acl_flags(system, result);
}

__attribute__((unused))
void op_ADC(System *system, AddressingMode addr_mode) {
    Operand operand = decode_operand(system, addr_mode);

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

    cpu_add_cycles(system, get_cycle_count(operand, addr_mode));
}

__attribute__((unused))
void op_AHX(System *system, AddressingMode addr_mode) {
    assert(false);
}

__attribute__((unused))
void op_ALR(System *system, AddressingMode addr_mode) {
    assert(false);
}

__attribute__((unused))
void op_ANC(System *system, AddressingMode addr_mode) {
    assert(false);
}

__attribute__((unused))
void op_AND(System *system, AddressingMode addr_mode) {
    Operand operand = decode_operand(system, addr_mode);
    byte value = read_operand(system, operand);
    byte acc = system->cpu.accumulator;

    byte result = acc & value;
    system->cpu.accumulator = result;

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

__attribute__((unused))
void op_ARR(System *system, AddressingMode addr_mode) {
    assert(false);
}

__attribute__((unused))
void op_ASL(System *system, AddressingMode addr_mode) {
    Operand operand = decode_operand(system, addr_mode);
    byte value = read_operand(system, operand);

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

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

__attribute__((unused))
void op_AXS(System *system, AddressingMode addr_mode) {
    assert(false);
}

__attribute__((unused))
void op_BCC(System *system, AddressingMode addr_mode) {
    op_branch(system, !cpu_get_flag(system, CPU_STATUS_CARRY_MASK));
}

__attribute__((unused))
void op_BCS(System *system, AddressingMode addr_mode) {
    op_branch(system, cpu_get_flag(system, CPU_STATUS_CARRY_MASK));
}

__attribute__((unused))
void op_BEQ(System *system, AddressingMode addr_mode) {
    op_branch(system, cpu_get_flag(system, CPU_STATUS_ZERO_MASK));
}

__attribute__((unused))
void op_BIT(System *system, AddressingMode addr_mode) {
    Operand operand = decode_operand(system, addr_mode);
    byte value = read_operand(system, operand);
    byte acc = system->cpu.accumulator;

    byte result = value & acc;

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

__attribute__((unused))
void op_BMI(System *system, AddressingMode addr_mode) {
    op_branch(system, cpu_get_flag(system, CPU_STATUS_NEGATIVE_MASK));
}

__attribute__((unused))
void op_BNE(System *system, AddressingMode addr_mode) {
    op_branch(system, !cpu_get_flag(system, CPU_STATUS_ZERO_MASK));
}

__attribute__((unused))
void op_BPL(System *system, AddressingMode addr_mode) {
    op_branch(system, !cpu_get_flag(system, CPU_STATUS_NEGATIVE_MASK));
}

// Stops program execution, useful for debugging
__attribute__((unused))
void op_BRK(System *system, AddressingMode addr_mode) {
    cpu_stack_push_context(system);

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

    assert(false);

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

__attribute__((unused))
void op_BVC(System *system, AddressingMode addr_mode) {
    op_branch(system, !cpu_get_flag(system, CPU_STATUS_OVERFLOW_MASK));
}

__attribute__((unused))
void op_BVS(System *system, AddressingMode addr_mode) {
    op_branch(system, cpu_get_flag(system, CPU_STATUS_OVERFLOW_MASK));
}

__attribute__((unused))
void op_CLC(System *system, AddressingMode addr_mode) {
    cpu_set_flag(system, CPU_STATUS_CARRY_MASK, false);
    cpu_add_cycles(system, 2);
}

__attribute__((unused))
void op_CLD(System *system, AddressingMode addr_mode) {
    cpu_set_flag(system, CPU_STATUS_DECIMAL_MASK, false);
    cpu_add_cycles(system, 2);
}

__attribute__((unused))
void op_CLI(System *system, AddressingMode addr_mode) {
    cpu_set_flag(system, CPU_STATUS_INTERRUPT_DISABLE_MASK, false);
    cpu_add_cycles(system, 2);
}

__attribute__((unused))
void op_CLV(System *system, AddressingMode addr_mode) {
    cpu_set_flag(system, CPU_STATUS_OVERFLOW_MASK, false);
    cpu_add_cycles(system, 2);
}

__attribute__((unused))
void op_CMP(System *system, AddressingMode addr_mode) {
    Operand operand = decode_operand(system, addr_mode);
    byte value = read_operand(system, operand);
    byte acc = system->cpu.accumulator;

    byte result = acc - value;

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

    cpu_add_cycles(system, get_cycle_count(operand, addr_mode));
}

__attribute__((unused))
void op_CPX(System *system, AddressingMode addr_mode) {
    Operand operand = decode_operand(system, addr_mode);
    byte value = read_operand(system, operand);
    byte x = system->cpu.x;

    byte result = x - value;

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

    cpu_add_cycles(system, get_cycle_count(operand, addr_mode));
}

__attribute__((unused))
void op_CPY(System *system, AddressingMode addr_mode) {
    Operand operand = decode_operand(system, addr_mode);
    byte value = read_operand(system, operand);
    byte y = system->cpu.y;

    byte result = y - value;

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

    cpu_add_cycles(system, get_cycle_count(operand, addr_mode));
}

__attribute__((unused))
void op_DCP(System *system, AddressingMode addr_mode) {
    Operand operand = decode_operand(system, addr_mode);
    byte value = read_operand(system, operand);
    byte acc = system->cpu.accumulator;

    byte result = value - 1;
    byte cmp_result = acc - result;

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

    write_operand(system, operand, result);

    byte cycle_count;
    switch (addr_mode) {
        case ADDR_MODE_ZERO_PAGE:
            cycle_count = 5;
            break;
        case ADDR_MODE_ZERO_PAGE_INDEXED_X:
        case ADDR_MODE_ABSOLUTE:
            cycle_count = 6;
            break;
        case ADDR_MODE_ABSOLUTE_INDEXED_X:
        case ADDR_MODE_ABSOLUTE_INDEXED_Y:
            cycle_count = 7;
            break;
        case ADDR_MODE_INDIRECT_X:
        case ADDR_MODE_INDIRECT_Y:
            cycle_count = 8;
            break;
        default:
            assert(false);
    }
    cpu_add_cycles(system, cycle_count);
}

__attribute__((unused))
void op_DEC(System *system, AddressingMode addr_mode) {
    Operand operand = decode_operand(system, addr_mode);
    byte value = read_operand(system, operand);

    byte result = value - 1;

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

__attribute__((unused))
void op_DEX(System *system, AddressingMode addr_mode) {
    byte x = system->cpu.x;

    byte result = x - 1;
    system->cpu.x = result;

    set_acl_flags(system, result);
    cpu_add_cycles(system, 2);
}

__attribute__((unused))
void op_DEY(System *system, AddressingMode addr_mode) {
    byte y = system->cpu.y;

    byte result = y - 1;
    system->cpu.y = result;

    set_acl_flags(system, result);
    cpu_add_cycles(system, 2);
}

__attribute__((unused))
void op_EOR(System *system, AddressingMode addr_mode) {
    Operand operand = decode_operand(system, addr_mode);
    byte value = read_operand(system, operand);
    byte acc = system->cpu.accumulator;

    acc ^= value;
    system->cpu.accumulator = acc;

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

__attribute__((unused))
void op_INC(System *system, AddressingMode addr_mode) {
    Operand operand = decode_operand(system, addr_mode);
    byte value = read_operand(system, operand);

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

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

__attribute__((unused))
void op_INX(System *system, AddressingMode addr_mode) {
    byte x = system->cpu.x;

    x += 1;
    system->cpu.x = x;

    set_acl_flags(system, x);
    cpu_add_cycles(system, 2);
}

__attribute__((unused))
void op_INY(System *system, AddressingMode addr_mode) {
    byte y = system->cpu.y;

    y += 1;
    system->cpu.y = y;

    set_acl_flags(system, y);
    cpu_add_cycles(system, 2);
}

__attribute__((unused))
void op_ISC(System *system, AddressingMode addr_mode) {
    Operand operand = decode_operand(system, addr_mode);
    byte value = read_operand(system, operand);

    value += 1;
    write_operand(system, operand, value);
    add_with_carry(system, ~value);

    cpu_add_cycles(system, get_shift_cycle_count(addr_mode));
}

__attribute__((unused))
void op_JMP(System *system, AddressingMode addr_mode) {
    word addr = decode_operand_addr(system, addr_mode, NULL);

    system->cpu.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.

    int cycle_count = 3;
    if (addr_mode == ADDR_MODE_INDIRECT_JUMP) {
        cycle_count = 5;
    }

    cpu_add_cycles(system, cycle_count);
}

__attribute__((unused))
void op_JSR(System *system, AddressingMode addr_mode) {
    // Push the program counter on the stack
    address program_counter = system->cpu.program_counter + 1;
    cpu_stack_push(system, program_counter >> 8);
    cpu_stack_push(system, program_counter & 0xff);

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

    cpu_add_cycles(system, 6);
}

__attribute__((unused))
void op_LAS(System *system, AddressingMode addr_mode) {
    assert(false);
}

__attribute__((unused))
void op_LAX(System *system, AddressingMode addr_mode) {
    Operand operand = decode_operand(system, addr_mode);
    byte value = read_operand(system, operand);

    system->cpu.accumulator = value;
    system->cpu.x = value;

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

__attribute__((unused))
void op_LDA(System *system, AddressingMode addr_mode) {
    Operand operand = decode_operand(system, addr_mode);
    byte value = read_operand(system, operand);

    system->cpu.accumulator = value;

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

__attribute__((unused))
void op_LDX(System *system, AddressingMode addr_mode) {
    Operand operand = decode_operand(system, addr_mode);
    byte value = read_operand(system, operand);

    system->cpu.x = value;

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

__attribute__((unused))
void op_LDY(System *system, AddressingMode addr_mode) {
    Operand operand = decode_operand(system, addr_mode);
    byte value = read_operand(system, operand);

    system->cpu.y = value;

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

__attribute__((unused))
void op_LSR(System *system, AddressingMode addr_mode) {
    Operand operand = decode_operand(system, addr_mode);
    byte value = read_operand(system, operand);

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

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

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

__attribute__((unused))
void op_NOP(System *system, AddressingMode addr_mode) {
    if (addr_mode != ADDR_MODE_IMPLICIT) {
        Operand operand = decode_operand(system, addr_mode);
        cpu_add_cycles(system, get_cycle_count(operand, addr_mode));
    } else {
        cpu_add_cycles(system, 2);
    }
}

__attribute__((unused))
void op_ORA(System *system, AddressingMode addr_mode) {
    Operand operand = decode_operand(system, addr_mode);
    byte value = read_operand(system, operand);
    byte acc = system->cpu.accumulator;

    acc |= value;
    system->cpu.accumulator = acc;

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

__attribute__((unused))
void op_PHA(System *system, AddressingMode addr_mode) {
    byte acc = system->cpu.accumulator;
    cpu_stack_push(system, acc);

    cpu_add_cycles(system, 3);
}

__attribute__((unused))
void op_PHP(System *system, AddressingMode addr_mode) {
    byte status = system->cpu.status;
    cpu_stack_push(system, status);

//    cpu_set_flag(system, CPU_STATUS_B_MASK, true);

    cpu_add_cycles(system, 3);
}

__attribute__((unused))
void op_PLA(System *system, AddressingMode addr_mode) {
    byte value = cpu_stack_pop(system);
    system->cpu.accumulator = value;

    set_acl_flags(system, value);

    cpu_add_cycles(system, 4);
}

__attribute__((unused))
void op_PLP(System *system, AddressingMode addr_mode) {
    byte value = cpu_stack_pop(system);

    value &= 0xef;  // The B mask cannot be set as it is a CPU signal
    value |= 0x20;  // This value is always set

    system->cpu.status = value;

    cpu_add_cycles(system, 4);
}

__attribute__((unused))
void op_RLA(System *system, AddressingMode addr_mode) {
    Operand operand = decode_operand(system, addr_mode);
    byte value = read_operand(system, operand);
    byte carry = cpu_get_flag(system, CPU_STATUS_CARRY_MASK);
    byte acc = system->cpu.accumulator;

    cpu_set_flag(system, CPU_STATUS_CARRY_MASK, value & 0x80);

    value = (value << 1) | carry;
    byte and_result = acc & value;
    system->cpu.accumulator = and_result;

    write_operand(system, operand, value);

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

__attribute__((unused))
void op_ROL(System *system, AddressingMode addr_mode) {
    Operand operand = decode_operand(system, addr_mode);
    byte value = read_operand(system, operand);
    byte carry = cpu_get_flag(system, CPU_STATUS_CARRY_MASK);

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

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

__attribute__((unused))
void op_ROR(System *system, AddressingMode addr_mode) {
    Operand operand = decode_operand(system, addr_mode);
    byte value = read_operand(system, operand);
    byte carry = cpu_get_flag(system, CPU_STATUS_CARRY_MASK);

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

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

__attribute__((unused))
void op_RRA(System *system, AddressingMode addr_mode) {
    Operand operand = decode_operand(system, addr_mode);
    byte value = read_operand(system, operand);
    byte carry = cpu_get_flag(system, CPU_STATUS_CARRY_MASK);

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

//    set_acl_flags(system, value);
    cpu_add_cycles(system, get_shift_cycle_count(addr_mode));
}

__attribute__((unused))
void op_RTI(System *system, AddressingMode addr_mode) {
    cpu_stack_pop_context(system);
    cpu_add_cycles(system, 6);
}

__attribute__((unused))
void op_RTS(System *system, AddressingMode addr_mode) {
    byte lo = cpu_stack_pop(system);
    address pc = cpu_stack_pop(system) << 8;
    pc += lo;

    system->cpu.program_counter = pc + 1;
    cpu_add_cycles(system, 6);
}

__attribute__((unused))
void op_SAX(System *system, AddressingMode addr_mode) {
    Operand operand = decode_operand(system, addr_mode);

    byte x = system->cpu.x;
    byte acc = system->cpu.accumulator;

    byte result = acc & x;
    write_operand(system, operand, result);

    cpu_add_cycles(system, get_cycle_count(operand, addr_mode));
}

__attribute__((unused))
void op_SBC(System *system, AddressingMode addr_mode) {
    Operand operand = decode_operand(system, addr_mode);
    byte value = read_operand(system, operand);

    add_with_carry(system, ~value);

    cpu_add_cycles(system, get_cycle_count(operand, addr_mode));
}

__attribute__((unused))
void op_SEC(System *system, AddressingMode addr_mode) {
    cpu_set_flag(system, CPU_STATUS_CARRY_MASK, true);
    cpu_add_cycles(system, 2);
}

__attribute__((unused))
void op_SED(System *system, AddressingMode addr_mode) {
    cpu_set_flag(system, CPU_STATUS_DECIMAL_MASK, true);
    cpu_add_cycles(system, 2);
}

__attribute__((unused))
void op_SEI(System *system, AddressingMode addr_mode) {
    cpu_set_flag(system, CPU_STATUS_INTERRUPT_DISABLE_MASK, true);
    cpu_add_cycles(system, 2);
}

__attribute__((unused))
void op_SHX(System *system, AddressingMode addr_mode) {
    assert(false);
}

__attribute__((unused))
void op_SHY(System *system, AddressingMode addr_mode) {
    assert(false);
}

__attribute__((unused))
void op_SLO(System *system, AddressingMode addr_mode) {
    Operand operand = decode_operand(system, addr_mode);
    byte value = read_operand(system, operand);
    byte acc = system->cpu.accumulator;

    byte result = value << 1;
    acc |= result;
    system->cpu.accumulator = acc;

    write_operand(system, operand, result);

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

__attribute__((unused))
void op_SRE(System *system, AddressingMode addr_mode) {
    Operand operand = decode_operand(system, addr_mode);
    byte value = read_operand(system, operand);
    byte acc = system->cpu.accumulator;

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

    value >>= 1;
    acc ^= value;
    system->cpu.accumulator = acc;
    write_operand(system, operand, value);

    set_acl_flags(system, acc);
    cpu_add_cycles(system, get_shift_cycle_count(addr_mode));
}

__attribute__((unused))
void op_STA(System *system, AddressingMode addr_mode) {
    Operand operand = decode_operand(system, addr_mode);
    byte acc = system->cpu.accumulator;
    assert(operand.type == OPERAND_TYPE_ADDRESS);

    mem_set_byte(system, operand.value, acc);

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

__attribute__((unused))
void op_STP(System *system, AddressingMode addr_mode) {
    assert(false);
}

__attribute__((unused))
void op_STX(System *system, AddressingMode addr_mode) {
    Operand operand = decode_operand(system, addr_mode);
    byte x = system->cpu.x;
    assert(operand.type == OPERAND_TYPE_ADDRESS);

    mem_set_byte(system, operand.value, x);

    cpu_add_cycles(system, get_cycle_count(operand, addr_mode));
}

__attribute__((unused))
void op_STY(System *system, AddressingMode addr_mode) {
    Operand operand = decode_operand(system, addr_mode);
    byte y = system->cpu.y;
    assert(operand.type == OPERAND_TYPE_ADDRESS);

    mem_set_byte(system, operand.value, y);

    cpu_add_cycles(system, get_cycle_count(operand, addr_mode));
}

__attribute__((unused))
void op_TAS(System *system, AddressingMode addr_mode) {
    assert(false);
}

__attribute__((unused))
void op_TAX(System *system, AddressingMode addr_mode) {
    byte acc = system->cpu.accumulator;
    system->cpu.x = acc;

    set_acl_flags(system, acc);
    cpu_add_cycles(system, 2);
}

__attribute__((unused))
void op_TAY(System *system, AddressingMode addr_mode) {
    byte acc = system->cpu.accumulator;
    system->cpu.y = acc;

    set_acl_flags(system, acc);
    cpu_add_cycles(system, 2);
}

__attribute__((unused))
void op_TSX(System *system, AddressingMode addr_mode) {
    byte value = system->cpu.stack_pointer;
    system->cpu.x = value;

    set_acl_flags(system, value);
    cpu_add_cycles(system, 2);
}

__attribute__((unused))
void op_TXA(System *system, AddressingMode addr_mode) {
    byte x = system->cpu.x;
    system->cpu.accumulator = x;

    set_acl_flags(system, x);
    cpu_add_cycles(system, 2);
}

__attribute__((unused))
void op_TXS(System *system, AddressingMode addr_mode) {
    byte x = system->cpu.x;
    system->cpu.stack_pointer = x;

    cpu_add_cycles(system, 2);
}

__attribute__((unused))
void op_TYA(System *system, AddressingMode addr_mode) {
    byte y = system->cpu.y;
    system->cpu.accumulator = y;

    set_acl_flags(system, y);
    cpu_add_cycles(system, 2);
}

__attribute__((unused))
void op_XAA(System *system, AddressingMode addr_mode) {
    assert(false);
}

void process_op_code(System *system, byte 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_JUMP)
        IS_OP_CODE_MODE(JMP, 0x6c, INDIRECT_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, ABSOLUTE_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(TXS, 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_X)
        IS_OP_CODE(NOP, 0xda)
        IS_OP_CODE_MODE(DEC, 0xde, ABSOLUTE_INDEXED_X)

        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_X)
        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(LAS, 0xbb, ABSOLUTE_INDEXED_Y)
        IS_OP_CODE_MODE(LAX, 0xbf, ABSOLUTE_INDEXED_Y)

        default:
            assert(false);
    }
}

char *get_op_code_name(byte op) {
    switch (op) {
        case 0x00:
            return "BRK";
        case 0x08:
            return "PHP";
        case 0x0b:
        case 0x2b:
            return "ANC";
        case 0x10:
            return "BPL";
        case 0x18:
            return "CLC";
        case 0x20:
            return "JSR";
        case 0x24:
        case 0x2c:
            return "BIT";
        case 0x28:
            return "PLP";
        case 0x30:
            return "BMI";
        case 0x38:
            return "SEC";
        case 0x40:
            return "RTI";
        case 0x48:
            return "PHA";
        case 0x4c:
        case 0x6c:
            return "JMP";
        case 0x50:
            return "BVC";
        case 0x58:
            return "CLI";
        case 0x60:
            return "RTS";
        case 0x68:
            return "PLA";
        case 0x70:
            return "BVS";
        case 0x78:
            return "SEI";
        case 0x84:
        case 0x8c:
        case 0x94:
            return "STY";
        case 0x88:
            return "DEY";
        case 0x90:
            return "BCC";
        case 0x98:
            return "TYA";
        case 0x9c:
            return "SHY";
        case 0xa0:
        case 0xa4:
        case 0xac:
        case 0xb4:
        case 0xbc:
            return "LDY";
        case 0xa8:
            return "TAY";
        case 0xb0:
            return "BCS";
        case 0xb8:
            return "CLV";
        case 0xc0:
        case 0xc4:
        case 0xcc:
            return "CPY";
        case 0xc8:
            return "INY";
        case 0xd0:
            return "BNE";
        case 0xd8:
            return "CLD";
        case 0xe0:
        case 0xe4:
        case 0xec:
            return "CPX";
        case 0xe8:
            return "INX";
        case 0xf0:
            return "BEQ";
        case 0xf8:
            return "SED";

        case 0x01:
        case 0x05:
        case 0x09:
        case 0x0d:
        case 0x11:
        case 0x15:
        case 0x19:
        case 0x1d:
            return "ORA";
        case 0x21:
        case 0x25:
        case 0x29:
        case 0x2d:
        case 0x31:
        case 0x35:
        case 0x39:
        case 0x3d:
            return "AND";
        case 0x41:
        case 0x45:
        case 0x49:
        case 0x4d:
        case 0x51:
        case 0x55:
        case 0x59:
        case 0x5d:
            return "EOR";
        case 0x61:
        case 0x65:
        case 0x69:
        case 0x6d:
        case 0x71:
        case 0x75:
        case 0x79:
        case 0x7d:
            return "ADC";
        case 0x81:
        case 0x85:
        case 0x8d:
        case 0x91:
        case 0x95:
        case 0x99:
        case 0x9d:
            return "STA";
        case 0xa1:
        case 0xa5:
        case 0xa9:
        case 0xad:
        case 0xb1:
        case 0xb5:
        case 0xb9:
        case 0xbd:
            return "LDA";
        case 0xc1:
        case 0xc5:
        case 0xc9:
        case 0xcd:
        case 0xd1:
        case 0xd5:
        case 0xd9:
        case 0xdd:
            return "CMP";
        case 0xe1:
        case 0xe5:
        case 0xe9:
        case 0xed:
        case 0xf1:
        case 0xf5:
        case 0xf9:
        case 0xfd:
            return "SBC";

        case 0x03:
        case 0x07:
        case 0x0f:
        case 0x13:
        case 0x17:
        case 0x1b:
        case 0x1f:
            return "SLO";
        case 0x23:
        case 0x27:
        case 0x2f:
        case 0x33:
        case 0x37:
        case 0x3b:
        case 0x3f:
            return "RLA";
        case 0x43:
        case 0x47:
        case 0x4f:
        case 0x53:
        case 0x57:
        case 0x5b:
        case 0x5f:
            return "SRE";
        case 0x4b:
            return "ALR";
        case 0x63:
        case 0x67:
        case 0x6f:
        case 0x73:
        case 0x77:
        case 0x7b:
        case 0x7f:
            return "RRA";
        case 0x6b:
            return "ARR";
        case 0x83:
        case 0x87:
        case 0x8f:
        case 0x97:
            return "SAX";
        case 0x8b:
            return "XAA";
        case 0x93:
        case 0x9f:
            return "AHX";
        case 0x9b:
            return "TAS";
        case 0xa3:
        case 0xa7:
        case 0xab:
        case 0xaf:
        case 0xb3:
        case 0xb7:
        case 0xbb:
        case 0xbf:
            return "LAX";
        case 0xc3:
        case 0xc7:
        case 0xcf:
        case 0xd3:
        case 0xd7:
        case 0xdb:
        case 0xdf:
            return "DCP";
        case 0xcb:
            return "AXS";
        case 0xe3:
        case 0xe7:
        case 0xef:
        case 0xf3:
        case 0xf7:
        case 0xfb:
        case 0xff:
            return "ISC";
        case 0xeb:
            return "SBC";

        case 0x06:
        case 0x0a:
        case 0x0e:
        case 0x16:
        case 0x1e:
            return "ASL";
        case 0x26:
        case 0x2a:
        case 0x2e:
        case 0x36:
        case 0x3e:
            return "ROL";
        case 0x46:
        case 0x4a:
        case 0x4e:
        case 0x56:
        case 0x5e:
            return "LSR";
        case 0x66:
        case 0x6a:
        case 0x6e:
        case 0x76:
        case 0x7e:
            return "ROR";
        case 0x86:
        case 0x8e:
        case 0x96:
            return "STX";
        case 0x8a:
            return "TXA";
        case 0x9a:
        case 0xba:
            return "TSX";
        case 0x9e:
            return "SHX";
        case 0xa2:
        case 0xa6:
        case 0xae:
        case 0xb6:
        case 0xbe:
            return "LDX";
        case 0xaa:
            return "TAX";
        case 0xc6:
        case 0xca:
        case 0xce:
        case 0xd6:
        case 0xde:
            return "DEC";
        case 0xe6:
        case 0xee:
        case 0xf6:
        case 0xfe:
            return "INC";

        case 0x02:
        case 0x12:
        case 0x22:
        case 0x32:
        case 0x42:
        case 0x52:
        case 0x62:
        case 0x72:
        case 0x92:
        case 0xb2:
        case 0xd2:
        case 0xf2:
            return "STP";
        case 0x04:
        case 0x0c:
        case 0x14:
        case 0x1c:
        case 0x1a:
        case 0x34:
        case 0x3a:
        case 0x3c:
        case 0x44:
        case 0x54:
        case 0x5a:
        case 0x5c:
        case 0x64:
        case 0x74:
        case 0x7a:
        case 0x7c:
        case 0x80:
        case 0x82:
        case 0x89:
        case 0xc2:
        case 0xd4:
        case 0xda:
        case 0xdc:
        case 0xe2:
        case 0xea:
        case 0xf4:
        case 0xfa:
        case 0xfc:
            return "NOP";

        default:
            assert(false);
    }
}