chip8.h

#pragma once

#include <iostream>
#include <array>
#include <map>
#include <random>

using onebyte = unsigned char;
using twobyte = unsigned short;

/* memory map of the system:
0x000 - 0x1FF: Chip 8 interpreter (contains font set in emu)
0x050 - 0x0A0: Used for the built in 4x5 pixel font set (0 - F)
0x200 - 0xFFF: Program ROM and work RAM

Original                 Implemented
+-+-+-+-+                +-+-+-+-+
|1|2|3|C|                |1|2|3|4|
+-+-+-+-+                +-+-+-+-+
|4|5|6|D|                |Q|W|E|R|
+-+-+-+-+       =>       +-+-+-+-+
|7|8|9|E|                |A|S|D|F|
+-+-+-+-+                +-+-+-+-+
|A|0|B|F|                |Z|X|C|V|
+-+-+-+-+                +-+-+-+-+ */

class Chip8 {
    using funcptr = void (Chip8::*)();

    static constexpr int MEM_SIZE = 4096;
    static constexpr int GFX_SIZE = 128*64;//64*32;
    static constexpr int REG_SIZE = 16;
    static constexpr int STK_SIZE = 16;
    static constexpr int KEY_SIZE = 16;
    static constexpr int FNT_SIZE = 80;
    //static constexpr int RPL_SIZE = 8;

    private:
    twobyte opcode = 0; // operation code, specifies the operation to be performed
    twobyte pc = 0x200; // program counter. increased by 2 because every instruction is 2 bytes long (except on jump or subroutine call)
    twobyte I = 0; // index register
    twobyte sp = 0; // stack pointer, holds the current level of the stack
    onebyte delayTimer = '\0', soundTimer = '\0'; // timers that count at 60 Hz
    bool waitForKey = false;

    std::array<onebyte, MEM_SIZE> memory{};
    std::array<onebyte, REG_SIZE> V{}; // CPU registers, V0-VE are general purpose and VF is the 'carry flag'
    std::array<onebyte, GFX_SIZE> gfx{}; // graphics (black and white, so 1 and 0)
    std::array<onebyte, KEY_SIZE> key{}; // current state of the HEX based keypad (0x0 - 0xF)
    std::array<twobyte, STK_SIZE> stack{}; // remembers the starting location before a subroutine call

    std::map<twobyte, funcptr> opMap; // maps the opcodes to their respective function

    std::random_device rd;
    std::mt19937 mt;
    std::uniform_int_distribution<int> dist;

    //bool extendedScreen = false;
    //bool forceExit = false;

    //std::array<onebyte, RPL_SIZE> rpl{}}; // RPL user flags

    public:
    bool drawFlag = true;

    public:
    Chip8() = default;
    Chip8(const Chip8& rhs) = delete;
    Chip8& operator=(const Chip8& rhs) = delete;
    ~Chip8() = default;

    onebyte gfxValueAt(unsigned int index) const;
    void mapKey(unsigned int index, onebyte value);
    //bool extendedScreenEnabled() const { return extendedScreen; };
    //bool forceExitEnabled() const { return forceExit; };

    void initialize();
    bool loadGame(const std::string& name);
    void emulateCycle();
    void updateTimers();

    private:
    void initOpMap();
    void fetchOpcode();
    void executeOpcode();

    // opcodes
    void CLS();
    void RET();
    //void EXIT();
    //void LOW();
    //void HIGH();
    void JP();
    void CALL();
    void SE();
    void SNE();
    void LD();
    void ADD();
    void OR();
    void AND();
    void XOR();
    void SUB();
    void SHR();
    void SUBN();
    void SHL();
    void RND();
    void DRW();
    void SKP();
    void SKNP();
};