path: root/src/chip8.cpp

#include "chip8.hpp"
#include "platform.hpp"

#include <fstream>
#include <iostream>
#include <cstdint>
#include <thread>
#include <mutex>

const uint32_t FONTSET_START_ADDRESS = 0x050;
const uint32_t ROM_START_ADDRESS = 0x200;

const uint32_t FONTSET_SIZE = 0x0a0 - FONTSET_START_ADDRESS;

uint8_t fontset[FONTSET_SIZE] = {
	0xF0, 0x90, 0x90, 0x90, 0xF0, // 0
	0x20, 0x60, 0x20, 0x20, 0x70, // 1
	0xF0, 0x10, 0xF0, 0x80, 0xF0, // 2
	0xF0, 0x10, 0xF0, 0x10, 0xF0, // 3
	0x90, 0x90, 0xF0, 0x10, 0x10, // 4
	0xF0, 0x80, 0xF0, 0x10, 0xF0, // 5
	0xF0, 0x80, 0xF0, 0x90, 0xF0, // 6
	0xF0, 0x10, 0x20, 0x40, 0x40, // 7
	0xF0, 0x90, 0xF0, 0x90, 0xF0, // 8
	0xF0, 0x90, 0xF0, 0x10, 0xF0, // 9
	0xF0, 0x90, 0xF0, 0x90, 0x90, // A
	0xE0, 0x90, 0xE0, 0x90, 0xE0, // B
	0xF0, 0x80, 0x80, 0x80, 0xF0, // C
	0xE0, 0x90, 0x90, 0x90, 0xE0, // D
	0xF0, 0x80, 0xF0, 0x80, 0xF0, // E
	0xF0, 0x80, 0xF0, 0x80, 0x80  // F
};

Chip8::Chip8() {
  pc = ROM_START_ADDRESS;

  for (uint32_t i = 0; i < FONTSET_SIZE; i++) {
    memory[FONTSET_START_ADDRESS + i] = fontset[i];
  }

  randGen = std::default_random_engine(
              std::chrono::system_clock::now()
                .time_since_epoch()
                .count()
            );
  randByte = std::uniform_int_distribution<uint8_t>(0, 255U);

  SetupTable();
}

void Chip8::SetupTable() {
  for (size_t i = 0; i <= sizeof(table0) / sizeof(table0[0]); i++) {
    table0[i] = &Chip8::OP_NULL;
    table8[i] = &Chip8::OP_NULL;
    tableE[i] = &Chip8::OP_NULL;
  }

  for (size_t i = 0; i <= sizeof(tableF) / sizeof(tableF[0]); i++) {
    tableF[i] = &Chip8::OP_NULL;
  }

  table[0x0] = &Chip8::Table0;
  table[0x1] = &Chip8::OP_1nnn;
  table[0x2] = &Chip8::OP_2nnn;
  table[0x3] = &Chip8::OP_3xkk;
  table[0x4] = &Chip8::OP_4xkk;
  table[0x5] = &Chip8::OP_5xy0;
  table[0x6] = &Chip8::OP_6xkk;
  table[0x7] = &Chip8::OP_7xkk;
  table[0x8] = &Chip8::Table8;
  table[0x9] = &Chip8::OP_9xy0;
  table[0xA] = &Chip8::OP_Annn;
  table[0xB] = &Chip8::OP_Bnnn;
  table[0xC] = &Chip8::OP_Cxkk;
  table[0xD] = &Chip8::OP_Dxyn;
  table[0xE] = &Chip8::TableE;
  table[0xF] = &Chip8::TableF;

  table0[0x0] = &Chip8::OP_00E0;
  table0[0xE] = &Chip8::OP_00EE;

  table8[0x0] = &Chip8::OP_8xy0;
  table8[0x1] = &Chip8::OP_8xy1;
  table8[0x2] = &Chip8::OP_8xy2;
  table8[0x3] = &Chip8::OP_8xy3;
  table8[0x4] = &Chip8::OP_8xy4;
  table8[0x5] = &Chip8::OP_8xy5;
  table8[0x6] = &Chip8::OP_8xy6;
  table8[0x7] = &Chip8::OP_8xy7;
  table8[0xE] = &Chip8::OP_8xyE;

  tableE[0x1] = &Chip8::OP_ExA1;
  tableE[0xE] = &Chip8::OP_Ex9E;

  tableF[0x07] = &Chip8::OP_Fx07;
  tableF[0x0A] = &Chip8::OP_Fx0A;
  tableF[0x15] = &Chip8::OP_Fx15;
  tableF[0x18] = &Chip8::OP_Fx18;
  tableF[0x1E] = &Chip8::OP_Fx1E;
  tableF[0x29] = &Chip8::OP_Fx29;
  tableF[0x33] = &Chip8::OP_Fx33;
  tableF[0x55] = &Chip8::OP_Fx55;
  tableF[0x65] = &Chip8::OP_Fx65;
}

void Chip8::Table0() {
  ((*this).*(table0[opcode & 0x000Fu]))();
}

void Chip8::Table8() {
  ((*this).*(table8[opcode & 0x000Fu]))();
}

void Chip8::TableE() {
  ((*this).*(tableE[opcode & 0x000Fu]))();
}

void Chip8::TableF() {
  ((*this).*(tableF[opcode & 0x00FFu]))();
}

void Chip8::Cycle() {
  // Fetch
  opcode = (memory[pc] << 8u) | memory[pc + 1];
  pc += 2;

  // Decode and Execute
  ((*this).*(table[(opcode & 0xF000u) >> 12u]))();
}

void Chip8::TimerUpdateThread(Platform* platform) {
    while (true) {
        std::this_thread::sleep_for(std::chrono::milliseconds(16));

        std::lock_guard<std::mutex> lock(timerMutex);
        if (delayTimer > 0) {
            delayTimer--;
        }

        if (soundTimer > 0) {
            soundTimer--;
            platform->StartBeep();
        } else {
          platform->StopBeep();
        }
    }
}

void Chip8::LoadROM(const char* filename) {
  // Open file as binary stream and seek to the end
  std::ifstream file(filename, std::ios::binary | std::ios::ate);

  if (file.is_open()) {
    // Get file size
    std::streampos size = file.tellg();
    // Allocate buffer
    char* buffer = new char[size];

    // Seek to the beginning
    file.seekg(0, std::ios::beg);
    // Populate the buffer
    file.read(buffer, size);
    file.close();

    // Load ROM contents into Chip8's memory, from 0x200
    for (uint64_t i = 0; i < size; i++) {
      memory[ROM_START_ADDRESS + i] = buffer[i];
    }

    // Free the buffer
    delete[] buffer;
  } else {
    std::cerr << "Error: Unable to open " << filename << std::endl;
    std::exit(1);
  }
}

// NULL: NOP
// Do nothing
void Chip8::OP_NULL() {}

// 00E0: CLS
// Clear the display
void Chip8::OP_00E0() {
  video.reset();
};

// 00EE: RET
// Return from a subroutine
void Chip8::OP_00EE() {
  sp--;
  pc = stack[sp];
}

// 1nnn: JP addr
// Jump to location nnn
void Chip8::OP_1nnn() {
  uint16_t address = opcode & 0x0FFFu;
  pc = address;
}

// 2nnn: CALL addr
// Call subroutine at nnn
void Chip8::OP_2nnn() {
  uint16_t address = opcode & 0x0FFFu;
  stack[sp] = pc;
  sp++;
  pc = address;
}

// 3xkk: SE Vx, byte
// Skip next instruction if Vx = kk
void Chip8::OP_3xkk() {
  uint8_t Vx = (opcode & 0x0F00u) >> 8u;
  uint8_t byte = opcode & 0x00FFu;

  if (registers[Vx] == byte)
    pc += 2;
}

// 4xkk: SNE Vx, byte
// Skip next instruction if Vx != kk
void Chip8::OP_4xkk() {
  uint8_t Vx = (opcode & 0x0F00u) >> 8u;
  uint8_t byte = opcode & 0x00FFu;

  if (registers[Vx] != byte)
    pc += 2;
}

// 5xy0: SE Vx, Vy
// Skip next instruction if Vx == Vy
void Chip8::OP_5xy0() {
  uint8_t Vx = (opcode & 0x0F00u) >> 8u;
  uint8_t Vy = (opcode & 0x00FFu) >> 4u;

  if (registers[Vx] == registers[Vy])
    pc += 2;
}

// 6xkk: LD Vx, byte
// Set Vx = kk
void Chip8::OP_6xkk() {
  uint8_t Vx = (opcode & 0x0F00u) >> 8u;
  uint8_t byte = opcode & 0x00FFu;

  registers[Vx] = byte;
}

// 7xkk: ADD Vx, byte
// Set Vx += kk
void Chip8::OP_7xkk() {
  uint8_t Vx = (opcode & 0x0F00u) >> 8u;
  uint8_t byte = opcode & 0x00FFu;

  registers[Vx] += byte;
}

// 8xy0: LD Vx, Vy
// Set Vx = Vy
void Chip8::OP_8xy0() {
  uint8_t Vx = (opcode & 0x0F00u) >> 8u;
  uint8_t Vy = (opcode & 0x00FFu) >> 4u;

  registers[Vx] = registers[Vy];
}

// 8xy1: OR Vx, Vy
// Set Vx = Vx OR Vy
void Chip8::OP_8xy1() {
  uint8_t Vx = (opcode & 0x0F00u) >> 8u;
  uint8_t Vy = (opcode & 0x00FFu) >> 4u;

  registers[Vx] |= registers[Vy];
}

// 8xy2: AND Vx, Vy
// Set Vx = Vx AND Vy
void Chip8::OP_8xy2() {
  uint8_t Vx = (opcode & 0x0F00u) >> 8u;
  uint8_t Vy = (opcode & 0x00FFu) >> 4u;

  registers[Vx] &= registers[Vy];
}

// 8xy3: XOR Vx, Vy
// Set Vx = Vx XOR Vy
void Chip8::OP_8xy3() {
  uint8_t Vx = (opcode & 0x0F00u) >> 8u;
  uint8_t Vy = (opcode & 0x00FFu) >> 4u;

  registers[Vx] ^= registers[Vy];
}

// 8xy4: ADD Vx, Vy
// Set Vx += Vy, set VF = carry
void Chip8::OP_8xy4() {
  uint8_t Vx = (opcode & 0x0F00u) >> 8u;
  uint8_t Vy = (opcode & 0x00FFu) >> 4u;

  uint16_t sum = registers[Vx] + registers[Vy];

  if (sum > 255u) {
    registers[0xF] = 1;
  } else {
    registers[0xF] = 0;
  }

  registers[Vx] = sum & 0xFFu;
}

// 8xy5: SUB Vx, Vy
// Set Vx -= Vy, set VF = NOT borrow
void Chip8::OP_8xy5() {
  uint8_t Vx = (opcode & 0x0F00u) >> 8u;
  uint8_t Vy = (opcode & 0x00FFu) >> 4u;

  if (registers[Vx] > registers[Vy]) {
    registers[0xF] = 1;
  } else {
    registers[0xF] = 0;
  }

  registers[Vx] -= registers[Vy];
}

// 8xy6: SHR Vx
// Set Vx = Vx SHR 1
void Chip8::OP_8xy6() {
  uint8_t Vx = (opcode & 0x0F00u) >> 8u;

  // Save LSB in VF
  registers[0xF] = (registers[Vx] & 0x1u);

  registers[Vx] >>= 1;
}

// 8xy7: SUBN Vx, Vy
// Set Vy -= Vx, set VF = NOT borrow
void Chip8::OP_8xy7() {
  uint8_t Vx = (opcode & 0x0F00u) >> 8u;
  uint8_t Vy = (opcode & 0x00FFu) >> 4u;

  if (registers[Vy] > registers[Vx]) {
    registers[0xF] = 1;
  } else {
    registers[0xF] = 0;
  }

  registers[Vx] = registers[Vy] - registers[Vx];
}

// 8xyE: SHL Vx
// Set Vx = Vx SHL 1
void Chip8::OP_8xyE() {
  uint8_t Vx = (opcode & 0x0F00u) >> 8u;

  // Save LSB in VF
  registers[0xF] = (registers[Vx] & 0x80u) >> 7u;

  registers[Vx] <<= 1;
}

// 9xy0: SNE Vx, Vy
// Skip next instruction if Vx != Vy
void Chip8::OP_9xy0() {
  uint8_t Vx = (opcode & 0x0F00u) >> 8u;
  uint8_t Vy = (opcode & 0x00FFu) >> 4u;

  if (registers[Vx] != registers[Vy])
    pc += 2;
}

// Annn: LD I, addr
// Set I = nnn
void Chip8::OP_Annn() {
  uint16_t address = opcode & 0x0FFFu;
  index = address;
}

// Bnnn: JP V0, addr
// Jump to location nnn + V0
void Chip8::OP_Bnnn() {
  uint16_t address = opcode & 0x0FFFu;
  pc = registers[0x0] + address;
}

// Cxkk: RND Vx, byte
// Set Vx = random byte AND kk
void Chip8::OP_Cxkk() {
  uint8_t Vx = (opcode & 0x0F00u) >> 8u;
  uint8_t byte = opcode & 0x00FFu;

  registers[Vx] = randByte(randGen) & byte;
}

// Dxyn: DRW Vx, Vy, nibble
// Display n-byte sprite starting at memory location I at (Vx, Vy), set VF = collision
void Chip8::OP_Dxyn() {
    uint8_t Vx = (opcode & 0x0F00u) >> 8u;
    uint8_t Vy = (opcode & 0x00F0u) >> 4u;
    uint8_t height = opcode & 0x000Fu;

    // Wrap if going beyond screen boundaries
    uint8_t xPos = registers[Vx] % VIDEO_WIDTH;
    uint8_t yPos = registers[Vy] % VIDEO_HEIGHT;

    registers[0xF] = 0;

    for (uint32_t row = 0; row < height; ++row) {
        uint8_t spriteByte = memory[index + row];
        for (uint32_t col = 0; col < 8; ++col) {
            uint8_t spritePixel = spriteByte & (0x80u >> col);

            // Calculate the coordinates in the video bitset
            int x = (xPos + col) % VIDEO_WIDTH;
            int y = (yPos + row) % VIDEO_HEIGHT;

            // Check collision and update the video bitset
            if (spritePixel) {
                if (video[y * VIDEO_WIDTH + x]) {
                    registers[0xF] = 1;
                }
                video[y * VIDEO_WIDTH + x].flip();
            }
        }
    }
}

// Ex9E: SKP Vx
// Skip next instruction if key with the value of Vx is pressed
void Chip8::OP_Ex9E() {
  uint8_t Vx = (opcode & 0x0F00u) >> 8u;
  uint8_t key = registers[Vx];

  if (keypad[key])
    pc += 2;
}

// ExA1: SKNP Vx
// Skip next instruction if key with the value of Vx is not pressed
void Chip8::OP_ExA1() {
  uint8_t Vx = (opcode & 0x0F00u) >> 8u;
  uint8_t key = registers[Vx];

  if (!keypad[key])
    pc += 2;
}

// Fx07: LD Vx, DT
// Set Vx = delay timer value
void Chip8::OP_Fx07() {
  uint8_t Vx = (opcode & 0x0F00u) >> 8u;
  registers[Vx] = delayTimer;
}

// Fx0A: LD Vx, K
// Wait for a key press, store the value of the key in Vx
void Chip8::OP_Fx0A() {
  uint8_t Vx = (opcode & 0x0F00u) >> 8u;
  for (uint16_t i = 0; i < 16; i++) {
    if (keypad[i]) {
      registers[Vx] = static_cast<uint8_t>(i);
      return;
    }
  }

  pc -= 2;
}

// Fx15: LD DT, Vx
// Set delay timer value = Vx
void Chip8::OP_Fx15() {
  uint8_t Vx = (opcode & 0x0F00u) >> 8u;
  delayTimer = registers[Vx];
}

// Fx18: LD ST, Vx
// Set sound timer value = Vx
void Chip8::OP_Fx18() {
  uint8_t Vx = (opcode & 0x0F00u) >> 8u;
  soundTimer = registers[Vx];
}

// Fx1E: ADD I, Vx
// Set I += Vx
void Chip8::OP_Fx1E() {
  uint8_t Vx = (opcode & 0x0F00u) >> 8u;
  index += registers[Vx];
}

// Fx29: LD F, Vx
// Set I = location of sprite for digit Vx
void Chip8::OP_Fx29() {
  uint8_t Vx = (opcode & 0x0F00u) >> 8u;
  uint8_t digit = registers[Vx];

  index = FONTSET_START_ADDRESS + (5 * digit);
}

// Fx33: LD B, Vx
// Store BCD representation of Vx in memory locations I, I+1, and I+2
void Chip8::OP_Fx33() {
  uint8_t Vx = (opcode & 0x0F00u) >> 8u;
  uint8_t value = registers[Vx];
  
  // Ones-place
  memory[index + 2] = value % 10;
  value /= 10;

  // Tens-place
  memory[index + 1] = value % 10;
  value /= 10;

  // Hundreds-place
  memory[index] = value % 10;
}

// Fx55: LD [I], Vx
// Store registers V0 through Vx in memory starting at location I
void Chip8::OP_Fx55() {
  uint8_t Vx = (opcode & 0x0F00u) >> 8u;
  
  for (uint8_t i = 0; i <= Vx; ++i) {
    memory[index + i] = registers[i];
  }
}

// Fx65: LD Vx, [I]
// Read registers V0 through Vx in memory starting at location I
void Chip8::OP_Fx65() {
  uint8_t Vx = (opcode & 0x0F00u) >> 8u;
  
  for (uint8_t i = 0; i <= Vx; ++i) {
    registers[i] = memory[index + i];
  }
}