scripts/cpp/chip8_disasm.cpp

#include <cstdint>
#include <cstdio>

#include <string>
#include <vector>

#include <iostream>
#include <fstream>
#include <filesystem>

template<typename T>
std::uint8_t get_nibble(T value, int nr) {
    return ((value >> (nr * 4)) & 0xF);
}

template<typename T>
std::vector<T> get_file_vector(std::ifstream& file_stream) {
    file_stream.seekg(0, std::ios::end);
    const std::size_t file_size = file_stream.tellg();
    file_stream.seekg(0, std::ios::beg);

    std::vector<T> file_contents(file_size);
    file_stream.read((char*)&file_contents[0], file_size);

    return file_contents;
}

void disassemble(const std::vector<std::uint16_t>& program) {
    for (auto inst : program) {
        if (inst == 0) {
            break;
        }

        switch (get_nibble(inst, 3)) {
        case 0x0:
            if (inst == 0x00E0) {
                printf("CLS\n");
            } else if (inst == 0x00EE) {
                printf("RET\n");
            } else {
                printf("SYS %03x\n", inst & 0xFFF);
            } break;

        case 0x1:
            printf("JMP %03x\n", inst & 0xFFF);
            break;

        case 0x2:
            printf("CALL %03x\n", inst & 0xFFF);
            break;

        case 0x3:
            printf("SE V%X, %02x\n", get_nibble(inst, 2), inst & 0xFF);
            break;

        case 0x4:
            printf("SNE V%X, %02x\n", get_nibble(inst, 2), inst & 0xFF);
            break;

        case 0x5:
            printf("SE V%X, V%X\n", get_nibble(inst, 2), get_nibble(inst, 1));
            break;

        case 0x6:
            printf("LD V%X, %02x\n", get_nibble(inst, 2), inst & 0xFF);
            break;

        case 0x7:
            printf("ADD V%X, %02x\n", get_nibble(inst, 2), inst & 0xFF);
            break;

        case 0x8:
            switch (inst & 0xF) {
            case 0x0:
                printf("LD V%X, V%X\n", get_nibble(inst, 2), get_nibble(inst, 1));
                break;

            case 0x1:
                printf("OR V%X, V%X\n", get_nibble(inst, 2), get_nibble(inst, 1));
                break;

            case 0x2:
                printf("AND V%X, V%X\n", get_nibble(inst, 2), get_nibble(inst, 1));
                break;

            case 0x3:
                printf("XOR V%X, V%X\n", get_nibble(inst, 2), get_nibble(inst, 1));
                break;

            case 0x4:
                printf("ADD V%X, V%X\n", get_nibble(inst, 2), get_nibble(inst, 1));
                break;

            case 0x5:
                printf("SUB V%X, V%X\n", get_nibble(inst, 2), get_nibble(inst, 1));
                break;

            case 0x6:
                printf("SHR V%X {, V%X}\n", get_nibble(inst, 2), get_nibble(inst, 1));
                break;

            case 0x7:
                printf("SUBN V%X V%X\n", get_nibble(inst, 2), get_nibble(inst, 1));
                break;

            case 0xE:
                printf("SHL V%X {, V%X}\n", get_nibble(inst, 2), get_nibble(inst, 1));
                break;

            default:
                break;
            } break;
        
        case 0x9:
            if (get_nibble(inst, 0) == 0) {
                printf("SNE V%X, V%X\n", get_nibble(inst, 2), get_nibble(inst, 1));
            } break;
        
        case 0xA:
            printf("LD I, %03x\n", inst & 0xFFF);
            break;
        
        case 0xB:
            printf("JP V0, %03x\n", inst & 0xFFF);
            break;

        case 0xC:
            printf("RND V%X, %02x\n", get_nibble(inst, 2), inst & 0xFF);
            break;

        case 0xD:
            printf("DRW V%X, V%X, %x\n", get_nibble(inst, 2), get_nibble(inst, 1), get_nibble(inst, 0));
            break;
        
        case 0xE:
            switch (inst & 0xFF) {
            case 0x9E:
                printf("SKP V%X\n", get_nibble(inst, 2));
                break;

            case 0xA1:
                printf("SKNP V%X\n", get_nibble(inst, 2));
                break;

            default:
                break;
            } break;

        case 0xF:
            switch (inst & 0xFF) {
            case 0x07:
                printf("LD V%X, DT\n", get_nibble(inst, 2));
                break;

            case 0x0A:
                printf("LD V%X, K\n", get_nibble(inst, 2));
                break;

            case 0x15:
                printf("LD DT, V%X\n", get_nibble(inst, 2));
                break;

            case 0x18:
                printf("LD ST, V%X\n", get_nibble(inst, 2));
                break;

            case 0x1E:
                printf("ADD I, V%X\n", get_nibble(inst, 2));
                break;

            case 0x29:
                printf("LD F, V%X\n", get_nibble(inst, 2));
                break;

            case 0x33:
                printf("LD B, V%X\n", get_nibble(inst, 2));
                break;

            case 0x55:
                printf("LD [I], V%X\n", get_nibble(inst, 2));
                break;

            case 0x65:
                printf("LD V%X, [I]\n", get_nibble(inst, 2));

            default:
                break;

            } break;

        default:
            break;

        }
    }
}

int main(int argc, char* argv[]) {
    if (argc < 2) {
        std::cout << "Usage: " << argv[0] << " [CHIP8 ROM]" << std::endl;
        return 1;
    }

    const std::string file_path = argv[1];

    if (!std::filesystem::exists(file_path)) {
        std::cout << "Could not find file." << std::endl;
        return 1;
    }

    std::ifstream file_stream(file_path, std::ios::binary);

    if (!file_stream) {
        std::cout << "Could not open file." << std::endl;
        return 1;
    }

    const auto file_contents = get_file_vector<std::uint16_t>(file_stream);

    disassemble(file_contents);
}