public SpanReader ReadAsSubReader(int length)
{
var reader = new SpanReader(_span.Slice(0, length));
Advance(length);
return(reader);
}
private void ReadTrainer(ref SpanReader span)
{
if (HasTrainer)
{
Trainer = span.ReadAsByteArray(512);
}
}
private void Load(byte[] content)
{
var span = new SpanReader(content);
ReadHeader(ref span);
ReadTrainer(ref span);
ReadPrgRom(ref span);
ReadChrRom(ref span);
Debug.Assert(span.IsCosumed, "nes not consumed.");
}
private void ReadHeader(ref SpanReader span)
{
if (span.ReadAsUnsignedInt() != _magicNumber)
{
throw new InvalidDataException("Invalid nes file.");
}
PrgRomSize = span.ReadAsByte() * 16u * 1024;
ChrRomSize = span.ReadAsByte() * 8u * 1024;
var flag6 = span.ReadAsByte();
MirroringMode = (MirroringMode)(flag6 & 0b1);
HasTrainer = (flag6 & 0b001) != 0;
var flag7 = span.ReadAsByte();
PrgRamSize = Math.Max((byte)1, span.ReadAsByte()) * 8u * 1024;
var flag9 = span.ReadAsByte();
var flag10 = span.ReadAsByte();
span.Advance(5);
}
private void ReadPrgRom(ref SpanReader span)
{
PrgRom = span.ReadAsByteArray((int)PrgRomSize);
}
private void ReadChrRom(ref SpanReader span)
{
ChrRom = span.ReadAsByteArray((int)ChrRomSize);
}