// Decode PKWare Compression Library stream.
public static byte[] Decompress(byte[] src)
{
var br = new BitReader(src);
// Are literals coded?
var coded = br.ReadBits(8);
if (coded < 0 || coded > 1)
{
throw new NotImplementedException("Invalid data stream");
}
var encodedLiterals = coded == 1;
// log2(dictionary size) - 6
var dict = br.ReadBits(8);
if (dict < 4 || dict > 6)
{
throw new InvalidDataException("Invalid dictionary size");
}
// output state
ushort next = 0; // index of next write location in out[]
var first = true; // true to check distances (for first 4K)
var outBuffer = new byte[MAXWIN]; // output buffer and sliding window
var ms = new MemoryStream();
// decode literals and length/distance pairs
do
{
// length/distance pair
if (br.ReadBits(1) == 1)
{
// Length
var symbol = Decode(lencode, br);
var len = lengthbase[symbol] + br.ReadBits(extra[symbol]);
// Magic number for "done"
if (len == 519)
{
for (var i = 0; i < next; i++)
{
ms.WriteByte(outBuffer[i]);
}
break;
}
// Distance
symbol = len == 2 ? 2 : dict;
var dist = Decode(distcode, br) << symbol;
dist += br.ReadBits(symbol);
dist++;
if (first && dist > next)
{
throw new InvalidDataException("Attempt to jump before data");
}
// copy length bytes from distance bytes back
do
{
var dest = next;
var source = dest - dist;
var copy = MAXWIN;
if (next < dist)
{
source += copy;
copy = dist;
}
copy -= next;
if (copy > len)
{
copy = len;
}
len -= copy;
next += (ushort)copy;
// copy with old-fashioned memcpy semantics
// in case of overlapping ranges. this is NOT
// the same as Array.Copy()
while (copy-- > 0)
{
outBuffer[dest++] = outBuffer[source++];
}
// Flush window to outstream
if (next == MAXWIN)
{
for (var i = 0; i < next; i++)
{
ms.WriteByte(outBuffer[i]);
}
next = 0;
first = false;
}
} while (len != 0);
}
else
{
// literal value
var symbol = encodedLiterals ? Decode(litcode, br) : br.ReadBits(8);
outBuffer[next++] = (byte)symbol;
if (next == MAXWIN)
{
for (var i = 0; i < next; i++)
{
ms.WriteByte(outBuffer[i]);
}
next = 0;
first = false;
}
}
} while (true);
return(ms.ToArray());
}
