public static DwgSectionLocator Parse(BitReader reader)
{
var recordNumber = reader.ReadByte();
var pointer = reader.ReadInt();
var length = reader.ReadInt();
return(new DwgSectionLocator(recordNumber, pointer, length));
}
public static void ValidateBytes(this BitReader reader, byte[] expectedBytes)
{
for (int i = 0; i < expectedBytes.Length; i++)
{
var b = reader.ReadByte();
if (b != expectedBytes[i])
{
throw new DwgReadException($"Invalid sentinel byte. Expected: 0x{expectedBytes[i]:X}, Actual: 0x{b:X}");
}
}
}
public static string Read_T(this BitReader reader)
{
var length = reader.Read_BS();
var sb = new StringBuilder();
for (int i = 0; i < length; i++)
{
sb.Append((char)reader.ReadByte());
}
return(sb.ToString());
}
public static DwgHandleReference Read_H(this BitReader reader)
{
var code = reader.ReadBits(4);
var counter = reader.ReadBits(4);
var offset = 0;
for (int i = 0; i < counter; i++)
{
var b = reader.ReadByte();
offset = (offset << 8) + b;
}
return(new DwgHandleReference((DwgHandleReferenceCode)code, offset));
}
public static int Read_BL(this BitReader reader)
{
var twoBits = reader.Read_BB();
switch (twoBits)
{
case 0b00:
return(reader.ReadInt());
case 0b01:
return(reader.ReadByte());
case 0b10:
return(0);
default:
throw new DwgReadException("Unsupported bit code.");
}
}
public static short Read_BS(this BitReader reader)
{
var twoBits = reader.Read_BB();
switch (twoBits)
{
case 0b00:
return(reader.ReadShort());
case 0b01:
return(reader.ReadByte());
case 0b10:
return(0);
default:
return(256);
}
}
public static int Read_MC(this BitReader reader, bool allowNegation = true)
{
// read bytes until no high bit
var bytes = new Stack <byte>();
byte b;
do
{
b = reader.ReadByte();
bytes.Push((byte)(b & 0x7F)); // only take lowest 7 bits
} while ((b & 0x80) != 0); // while high bit set
bool negate = false;
if (allowNegation && (b & 0x40) != 0)
{
negate = true;
bytes.Pop();
bytes.Push((byte)(b & 0x3F));
}
// re-create number
int result = 0;
while (bytes.Any())
{
result = (result << 7) + bytes.Pop();
}
if (negate)
{
result *= -1;
}
return(result);
}
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);
}
public static byte Read_RC(this BitReader reader)
{
return(reader.ReadByte());
}
