GameBoy\Core::memoryRead PHP Method

    public function memoryRead($address)
    {
        if ($address < 0x4000) {
            return $this->memory[$address];
        } elseif ($address < 0x8000) {
            return $this->ROM[$this->currentROMBank + $address];
        } elseif ($address >= 0x8000 && $address < 0xa000) {
            if ($this->cGBC) {
                //CPU Side Reading The VRAM (Optimized for GameBoy Color)
                return $this->lcdController->modeSTAT > 2 ? 0xff : ($this->currVRAMBank == 0 ? $this->memory[$address] : $this->VRAM[$address - 0x8000]);
            }
            //CPU Side Reading The VRAM (Optimized for classic GameBoy)
            return $this->lcdController->modeSTAT > 2 ? 0xff : $this->memory[$address];
        } elseif ($address >= 0xa000 && $address < 0xc000) {
            if ($this->numRAMBanks == 1 / 16 && $address < 0xa200 || $this->numRAMBanks >= 1) {
                if (!$this->cMBC3) {
                    //memoryReadMBC
                    //Switchable RAM
                    if ($this->MBCRAMBanksEnabled || Settings::$overrideMBC) {
                        return $this->MBCRam[$address + $this->currMBCRAMBankPosition];
                    }
                    //cout("Reading from disabled RAM.", 1);
                    return 0xff;
                } else {
                    //MBC3 RTC + RAM:
                    //memoryReadMBC3
                    //Switchable RAM
                    if ($this->MBCRAMBanksEnabled || Settings::$overrideMBC) {
                        switch ($this->currMBCRAMBank) {
                            case 0x0:
                            case 0x1:
                            case 0x2:
                            case 0x3:
                                return $this->MBCRam[$address + $this->currMBCRAMBankPosition];
                                break;
                            case 0x8:
                                return $this->latchedSeconds;
                                break;
                            case 0x9:
                                return $this->latchedMinutes;
                                break;
                            case 0xa:
                                return $this->latchedHours;
                                break;
                            case 0xb:
                                return $this->latchedLDays;
                                break;
                            case 0xc:
                                return ($this->RTCDayOverFlow ? 0x80 : 0) + ($this->RTCHALT ? 0x40 : 0) + $this->latchedHDays;
                        }
                    }
                    //cout("Reading from invalid or disabled RAM.", 1);
                    return 0xff;
                }
            } else {
                return 0xff;
            }
        } elseif ($address >= 0xc000 && $address < 0xe000) {
            if (!$this->cGBC || $address < 0xd000) {
                return $this->memory[$address];
            } else {
                //memoryReadGBCMemory
                return $this->GBCMemory[$address + $this->gbcRamBankPosition];
            }
        } elseif ($address >= 0xe000 && $address < 0xfe00) {
            if (!$this->cGBC || $address < 0xf000) {
                //memoryReadECHONormal
                return $this->memory[$address - 0x2000];
            } else {
                //memoryReadECHOGBCMemory
                return $this->GBCMemory[$address + $this->gbcRamBankPositionECHO];
            }
        } elseif ($address < 0xfea0) {
            //memoryReadOAM
            return $this->lcdController->modeSTAT > 1 ? 0xff : $this->memory[$address];
        } elseif ($this->cGBC && $address >= 0xfea0 && $address < 0xff00) {
            //memoryReadNormal
            return $this->memory[$address];
        } elseif ($address >= 0xff00) {
            switch ($address) {
                case 0xff00:
                    return 0xc0 | $this->memory[0xff00];
                    //Top nibble returns as set.
                    break;
                case 0xff01:
                    return ($this->memory[0xff02] & 0x1) == 0x1 ? 0xff : $this->memory[0xff01];
                    break;
                case 0xff02:
                    if ($this->cGBC) {
                        return 0x7c | $this->memory[0xff02];
                    } else {
                        return 0x7e | $this->memory[0xff02];
                    }
                    break;
                case 0xff07:
                    return 0xf8 | $this->memory[0xff07];
                    break;
                case 0xff0f:
                    return 0xe0 | $this->memory[0xff0f];
                    break;
                case 0xff10:
                    return 0x80 | $this->memory[0xff10];
                    break;
                case 0xff11:
                    return 0x3f | $this->memory[0xff11];
                    break;
                case 0xff14:
                    return 0xbf | $this->memory[0xff14];
                    break;
                case 0xff16:
                    return 0x3f | $this->memory[0xff16];
                    break;
                case 0xff19:
                    return 0xbf | $this->memory[0xff19];
                    break;
                case 0xff1a:
                    return 0x7f | $this->memory[0xff1a];
                    break;
                case 0xff1b:
                    return 0xff;
                    break;
                case 0xff1c:
                    return 0x9f | $this->memory[0xff1c];
                    break;
                case 0xff1e:
                    return 0xbf | $this->memory[0xff1e];
                    break;
                case 0xff20:
                    return 0xff;
                    break;
                case 0xff23:
                    return 0xbf | $this->memory[0xff23];
                    break;
                case 0xff26:
                    return 0x70 | $this->memory[0xff26];
                    break;
                case 0xff30:
                case 0xff31:
                case 0xff32:
                case 0xff33:
                case 0xff34:
                case 0xff35:
                case 0xff36:
                case 0xff37:
                case 0xff38:
                case 0xff39:
                case 0xff3a:
                case 0xff3b:
                case 0xff3c:
                case 0xff3d:
                case 0xff3e:
                case 0xff3f:
                    return ($this->memory[0xff26] & 0x4) == 0x4 ? 0xff : $this->memory[$address];
                    break;
                case 0xff41:
                    return 0x80 | $this->memory[0xff41] | $this->lcdController->modeSTAT;
                    break;
                case 0xff44:
                    return $this->lcdController->LCDisOn ? $this->memory[0xff44] : 0;
                    break;
                case 0xff4f:
                    return $this->currVRAMBank;
                    break;
                default:
                    //memoryReadNormal
                    return $this->memory[$address];
            }
        } else {
            //memoryReadBAD
            return 0xff;
        }
    }

 /**
  * Opcode #0xFE.
  *
  * CP n
  *
  * @param Core $core
  */
 public static function opcode254(Core $core)
 {
     $dirtySum = $core->registerA - $core->memoryRead($core->programCounter);
     $core->FHalfCarry = ($core->unsbtub($dirtySum) & 0xf) > ($core->registerA & 0xf);
     $core->FCarry = $dirtySum < 0;
     $core->FZero = $dirtySum == 0;
     $core->programCounter = $core->programCounter + 1 & 0xffff;
     $core->FSubtract = true;
 }