internal static DwgFileHeader Parse(BitReader reader) { reader.StartCrcCheck(); var versionString = reader.ReadStringAscii(6); var version = DwgVersionIdExtensions.VersionIdFromString(versionString); var unknown1 = reader.ReadBytes(6); var maintVer = 0; if (version == DwgVersionId.R14) { maintVer = unknown1[5]; } var marker = reader.ReadByte(); if (marker != 1) { throw new DwgReadException("Expected value of 1 at offset 13."); } var imagePointer = reader.ReadInt(); var unknown2 = reader.ReadBytes(2); var codePage = reader.ReadShort(); var header = new DwgFileHeader(version, maintVer, imagePointer, codePage); var recordLocatorCount = reader.ReadInt(); for (int i = 0; i < recordLocatorCount; i++) { var locator = DwgSectionLocator.Parse(reader); switch (i) { case 0: header.HeaderVariablesLocator = locator; break; case 1: header.ClassSectionLocator = locator; break; case 2: header.ObjectMapLocator = locator; break; case 3: header.UnknownSection_R13C3AndLaterLocator = locator; break; case 4: header.UnknownSection_PaddingLocator = locator; break; } } ushort crcXorValue; switch (recordLocatorCount) { case 0: case 1: case 2: crcXorValue = 0; break; case 3: crcXorValue = 0xAD98; break; case 4: crcXorValue = 0x8101; break; case 5: crcXorValue = 0x3CC4; break; case 6: crcXorValue = 0x8461; break; default: throw new DwgReadException("Unsupported record locator count."); } reader.ValidateCrc(xorValue: crcXorValue); reader.ValidateSentinel(HeaderSentinel); return(header); }