private BufferPtr NextLine()
{
var pbRet = BufferPtr.FromPtr(_pbBitsOutCur);
_pbBitsOutCur.Incr(_cbStride); // f*****g upside down dibs!
_linesLeft--;
return(pbRet);
}
public void Decompress(out byte[] data, out int length)
{
int fc;
// Initialize for decoding a new image...
const int size = 8;
InitExp(size);
// Initialize in case they forgot to put in a clear code.
// (This shouldn't happen, but we'll try and decode it anyway...)
var oc = fc = 0;
// Allocate space for the decode buffer
var buf = NextLine();
// Set up the stack pointer and decode buffer pointer
var sp = new BufferPtr(_stack);
var bufPtr = BufferPtr.FromPtr(buf);
var bufCnt = _width;
// This is the main loop. For each code we get we pass through the
// linked list of prefix codes, pushing the corresponding "character" for
// each code onto the stack. When the list reaches a single "character"
// we push that on the stack too, and then start unstacking each
// character for output in the correct order. Special handling is
// included for the clear code, and the whole thing ends when we get
// an ending code.
var c = GetNextCode();
while (c != _ending)
{
// If we had a file error, return without completing the decode
if (c < 0)
{
break;
}
// If the code is a clear code, reinitialize all necessary items.
if (c == _clear)
{
_currSize = size + 1;
_slot = _newCodes;
_topSlot = 1 << _currSize;
// Continue reading codes until we get a non-clear code
// (Another unlikely, but possible case...)
c = GetNextCode();
while (c == _clear)
{
c = GetNextCode();
}
// If we get an ending code immediately after a clear code
// (Yet another unlikely case), then break out of the loop.
if (c == _ending)
{
break;
}
// Finally, if the code is beyond the range of already set codes,
// (This one had better NOT happen... I have no idea what will
// result from this, but I doubt it will look good...) then set it
// to color zero.
if (c >= _slot)
{
c = 0;
}
oc = fc = c;
// And var us not forget to put the char into the buffer... And
// if, on the off chance, we were exactly one pixel from the end
// of the line, we have to send the buffer to the out_line()
// routine...
bufPtr.Set((byte)c);
bufPtr.Incr();
if (--bufCnt == 0)
{
buf = NextLine();
bufPtr = BufferPtr.FromPtr(buf);
bufCnt = _width;
}
}
else
{
// In this case, it's not a clear code or an ending code, so
// it must be a code code... So we can now decode the code into
// a stack of character codes. (Clear as mud, right?)
var code = c;
// Here we go again with one of those off chances... If, on the
// off chance, the code we got is beyond the range of those already
// set up (Another thing which had better NOT happen...) we trick
// the decoder into thinking it actually got the last code read.
// (Hmmn... I'm not sure why this works... But it does...)
if (code >= _slot)
{
if (code > _slot)
{
++_badCodeCount;
}
code = oc;
sp.Set((byte)fc);
sp.Incr();
}
// Here we scan back along the linked list of prefixes, pushing
// helpless characters (ie. suffixes) onto the stack as we do so.
while (code >= _newCodes)
{
sp.Set(_suffix[code]);
sp.Incr();
code = _prefix[code];
}
// Push the last character on the stack, and set up the new
// prefix and suffix, and if the required slot number is greater
// than that allowed by the current bit size, increase the bit
// size. (NOTE - If we are all full, we *don't* save the new
// suffix and prefix... I'm not certain if this is correct...
// it might be more proper to overwrite the last code...
sp.Set((byte)code);
sp.Incr();
if (_slot < _topSlot)
{
fc = code;
_suffix[_slot] = (byte)fc; // = code;
_prefix[_slot++] = oc;
oc = c;
}
if (_slot >= _topSlot)
{
if (_currSize < 12)
{
_topSlot <<= 1;
++_currSize;
}
}
// Now that we've pushed the decoded string (in reverse order)
// onto the stack, lets pop it off and put it into our decode
// buffer... And when the decode buffer is full, write another
// line...
while (sp.GetPos() > 0)
{
sp.Decr();
bufPtr.Set(sp.Get());
bufPtr.Incr();
if (--bufCnt == 0)
{
buf = NextLine();
bufPtr = buf;
bufCnt = _width;
}
}
}
c = GetNextCode();
}
data = _pbBitsOutCur.GetBuffer();
length = _pstm.GetPos();
}