private uint ReadFilterData(BitInput Inp)
{
uint ByteCount = (Inp.fgetbits() >> 14) + 1;
Inp.addbits(2);
uint Data = 0;
for (uint I = 0; I < ByteCount; I++)
{
Data += (Inp.fgetbits() >> 8) << (int)(I * 8);
Inp.addbits(8);
}
return(Data);
}
private uint DecodeNumber(BitInput Inp, DecodeTable Dec)
{
// Left aligned 15 bit length raw bit field.
uint BitField = Inp.getbits() & 0xfffe;
if (BitField < Dec.DecodeLen[Dec.QuickBits])
{
uint Code = BitField >> (int)(16 - Dec.QuickBits);
Inp.addbits(Dec.QuickLen[Code]);
return(Dec.QuickNum[Code]);
}
// Detect the real bit length for current code.
uint Bits = 15;
for (uint I = Dec.QuickBits + 1; I < 15; I++)
{
if (BitField < Dec.DecodeLen[I])
{
Bits = I;
break;
}
}
Inp.addbits(Bits);
// Calculate the distance from the start code for current bit length.
uint Dist = BitField - Dec.DecodeLen[Bits - 1];
// Start codes are left aligned, but we need the normal right aligned
// number. So we shift the distance to the right.
Dist >>= (int)(16 - Bits);
// Now we can calculate the position in the code list. It is the sum
// of first position for current bit length and right aligned distance
// between our bit field and start code for current bit length.
uint Pos = Dec.DecodePos[Bits] + Dist;
// Out of bounds safety check required for damaged archives.
if (Pos >= Dec.MaxNum)
{
Pos = 0;
}
// Convert the position in the code list to position in alphabet
// and return it.
return(Dec.DecodeNum[Pos]);
}
private bool ReadBlockHeader(BitInput Inp, ref UnpackBlockHeader Header)
{
Header.HeaderSize = 0;
if (!Inp.ExternalBuffer && Inp.InAddr > ReadTop - 7)
{
if (!UnpReadBuf())
{
return(false);
}
}
Inp.faddbits((uint)((8 - Inp.InBit) & 7));
byte BlockFlags = (byte)(Inp.fgetbits() >> 8);
Inp.faddbits(8);
uint ByteCount = (uint)(((BlockFlags >> 3) & 3) + 1); // Block size byte count.
if (ByteCount == 4)
{
return(false);
}
Header.HeaderSize = (int)(2 + ByteCount);
Header.BlockBitSize = (BlockFlags & 7) + 1;
byte SavedCheckSum = (byte)(Inp.fgetbits() >> 8);
Inp.faddbits(8);
int BlockSize = 0;
for (uint I = 0; I < ByteCount; I++)
{
BlockSize += (int)((Inp.fgetbits() >> 8) << (int)(I * 8));
Inp.addbits(8);
}
Header.BlockSize = BlockSize;
byte CheckSum = (byte)(0x5a ^ BlockFlags ^ BlockSize ^ (BlockSize >> 8) ^ (BlockSize >> 16));
if (CheckSum != SavedCheckSum)
{
return(false);
}
Header.BlockStart = Inp.InAddr;
ReadBorder = Math.Min(ReadBorder, Header.BlockStart + Header.BlockSize - 1);
Header.LastBlockInFile = (BlockFlags & 0x40) != 0;
Header.TablePresent = (BlockFlags & 0x80) != 0;
return(true);
}
private uint SlotToLength(BitInput Inp, uint Slot)
{
uint LBits, Length = 2;
if (Slot < 8)
{
LBits = 0;
Length += Slot;
}
else
{
LBits = Slot / 4 - 1;
Length += (4 | (Slot & 3)) << (int)LBits;
}
if (LBits > 0)
{
Length += Inp.getbits() >> (int)(16 - LBits);
Inp.addbits(LBits);
}
return(Length);
}
