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_MS(this BitReader reader)
{
// read shorts until no high bit
var shorts = new Stack <short>();
short s;
do
{
s = reader.ReadShort();
shorts.Push((short)(s & 0x7FFF)); // only take the lowest 15 bits
} while ((s & 0x8000) != 0); // while high bit set
// re-create number
int result = 0;
while (shorts.Any())
{
result = (result << 15) + shorts.Pop();
}
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 short Read_RS(this BitReader reader)
{
return(reader.ReadShort());
}
