/// Frame::ComputeMCUSizes
// Compute the MCU sizes of the components from the subsampling values
void Frame::ComputeMCUSizes(void)
{
UBYTE i;
UWORD maxx,maxy;
// Compute the maximum MCU width and height.
assert(m_ppComponent[0]);
maxx = m_ppComponent[0]->SubXOf();
maxy = m_ppComponent[0]->SubYOf();
for(i = 1;i < m_ucDepth;i++) {
assert(m_ppComponent[i]);
maxx = m_ppComponent[i]->SubXOf() * maxx / gcd(m_ppComponent[i]->SubXOf(),maxx);
maxy = m_ppComponent[i]->SubYOf() * maxy / gcd(m_ppComponent[i]->SubYOf(),maxy);
if (maxx > MAX_UBYTE || maxy > MAX_UBYTE)
JPG_THROW(OVERFLOW_PARAMETER,"Frame::ComputeMCUSizes",
"the smallest common multiple of all subsampling factors must be smaller than 255");
}
m_ucMaxMCUWidth = maxx;
m_ucMaxMCUHeight = maxy;
for(i = 0;i < m_ucDepth;i++) {
m_ppComponent[i]->SetMCUSize(maxx,maxy);
}
//
// Check whether the scm is actually part of the MCU sizes written. If not,
// then JPEG cannot support this subsampling setting. Wierd.
for(i = 0;i < m_ucDepth;i++) {
if (m_ppComponent[i]->SubXOf() != m_ucMaxMCUWidth / m_ppComponent[i]->MCUWidthOf() ||
m_ppComponent[i]->SubYOf() != m_ucMaxMCUHeight / m_ppComponent[i]->MCUHeightOf())
JPG_THROW(INVALID_PARAMETER,"Frame::ComputeMCUSizes",
"the given set of subsampling parameters is not supported by JPEG");
}
}
/// HuffmanTemplate::ParseMarker
void HuffmanTemplate::ParseMarker(class ByteStream *io)
{
ULONG i,total = 0;
// A new decoder chain is required here.
delete m_pDecoder;
m_pDecoder = NULL;
delete m_pEncoder;
m_pEncoder = NULL;
// Read the number of huffman codes of length i-1
for(i = 0; i < 16U; i++) {
LONG cnt = io->Get();
if (cnt == ByteStream::EOF)
JPG_THROW(MALFORMED_STREAM,"HuffmanTemplate::ParseMarker","huffman table marker run out of data");
m_ucLengths[i] = cnt;
total += cnt;
}
m_ulCodewords = total;
assert(m_pucValues == NULL);
m_pucValues = (UBYTE *)m_pEnviron->AllocMem(sizeof(UBYTE) * total);
for(i = 0; i < total; i++) {
LONG v = io->Get();
if (v == ByteStream::EOF)
JPG_THROW(MALFORMED_STREAM,"HuffmanTemplate::ParseMarker","huffman table marker run out of data");
m_pucValues[i] = v;
}
}
/// Frame::DefineComponent
// Define a component for writing. Must be called exactly once per component for encoding.
// idx is the component index (not its label, which is generated automatically), and
// the component subsampling factors.
class Component *Frame::DefineComponent(UBYTE idx,UBYTE subx,UBYTE suby)
{
if (m_ucDepth == 0)
JPG_THROW(OBJECT_DOESNT_EXIST,"Frame::DefineComponent",
"Frame depth must be specified first before defining the component properties");
if (m_ucPrecision == 0)
JPG_THROW(OBJECT_DOESNT_EXIST,"Frame::DefineComponent",
"Frame precision must be specified first before defining the component properties");
if (idx >= m_ucDepth)
JPG_THROW(OVERFLOW_PARAMETER,"Frame::DefineComponent",
"component index is out of range, must be between 0 and depth-1");
if (m_ppComponent == NULL) {
m_ppComponent = (class Component **)m_pEnviron->AllocMem(sizeof(class Component *) * m_ucDepth);
memset(m_ppComponent,0,sizeof(class Component *) * m_ucDepth);
}
if (m_ppComponent[idx])
JPG_THROW(OBJECT_EXISTS,"Frame::DefineComponent",
"the indicated component is already defined");
m_ppComponent[idx] = new(m_pEnviron) Component(m_pEnviron,idx,m_ucPrecision,subx,suby);
return m_ppComponent[idx];
}
/// Tables::FindQuantizationTable
// Find the quantization table of the given index.
const UWORD *Tables::FindQuantizationTable(UBYTE idx) const
{
const UWORD *t;
if (m_pQuant == NULL)
JPG_THROW(OBJECT_DOESNT_EXIST,"Tables::FindQuantizationTable","DQT marker missing, no quantization table defined");
t = m_pQuant->QuantizationTable(idx);
if (t == NULL)
JPG_THROW(OBJECT_DOESNT_EXIST,"Tables::FindQuantizationTable","requested quantization matrix not defined");
return t;
}
/// Tables::FindACHuffmanTable
// Find the AC huffman table of the indicated index.
class HuffmanTemplate *Tables::FindACHuffmanTable(UBYTE idx,ScanType type,UBYTE depth,UBYTE hidden,bool residual) const
{
class HuffmanTemplate *t;
if (m_pHuffman == NULL)
JPG_THROW(OBJECT_DOESNT_EXIST,"Tables::FindACHuffmanTable","DHT marker missing for huffman encoded scan");
t = m_pHuffman->ACTemplateOf(idx,type,depth,hidden,residual);
if (t == NULL)
JPG_THROW(OBJECT_DOESNT_EXIST,"Tables::FindACHuffmanTable","requested AC huffman coding table not defined");
return t;
}
void BitStream<bitstuffing>::ReportError(void)
{
class Environ *m_pEnviron = m_pIO->EnvironOf();
if (m_bEOF)
JPG_THROW(UNEXPECTED_EOF,"BitStream::ReportError",
"invalid stream, found EOF within entropy coded segment");
if (m_bMarker)
JPG_THROW(UNEXPECTED_EOF,"BitStream::ReportError",
"invalid stream, found marker in entropy coded segment");
JPG_THROW(MALFORMED_STREAM,"BitStream::ReportError",
"invalid stream, found invalid huffman code in entropy coded segment");
}
/// ACTemplate::ParseACMarker
// Parse off an AC conditioning parameter.
void ACTemplate::ParseACMarker(class ByteStream *io)
{
LONG ac = io->Get();
if (ac == ByteStream::EOF)
JPG_THROW(MALFORMED_STREAM,"ACTemplate::ParseACMarker",
"unexpected EOF while parsing off the AC conditioning parameters");
if (ac < 1 || ac > 63)
JPG_THROW(MALFORMED_STREAM,"ACTemplate::ParseACMarker",
"AC conditoning parameter must be between 1 and 63");
m_ucBlockEnd = ac;
}
/// PredictorBase::CreatePredictorChain
// Create a prediction chain for the given neutral value and
// the given prediction mode. The mode "none" is used to
// indicate the differential mode.
// This requires an array of four predictors to be used for
// life-time management. The first element is the initial predictor.
void PredictorBase::CreatePredictorChain(class Environ *m_pEnviron,class PredictorBase *chain[4],
PredictionMode mode,UBYTE preshift,
LONG neutral)
{
if (preshift > 20)
JPG_THROW(OVERFLOW_PARAMETER,"PredictorBase::CreatePredictorChain",
"lossless predictive point transformation value is out of range, no code provisioned for it");
assert(chain[0] == NULL && chain[1] == NULL && chain[2] == NULL && chain[3] == NULL);
switch(mode) {
case None:
// This is differential. It only requires a single predictor.
chain[0] = CreatePredictor(m_pEnviron,mode,preshift,0);
assert(chain[0]);
// This predictor stays the same no matter how we move.
chain[0]->m_pNextRight = chain[0];
chain[0]->m_pNextDown = chain[0];
break;
case Left:
case Top:
case LeftTop:
case Linear:
case WeightA:
case WeightB:
case Diagonal:
// It starts with the neutral predictor top left.
chain[0] = CreatePredictor(m_pEnviron,Neutral,preshift,neutral);
chain[1] = CreatePredictor(m_pEnviron,Left ,preshift,0);
chain[2] = CreatePredictor(m_pEnviron,Top ,preshift,0);
chain[3] = CreatePredictor(m_pEnviron,mode ,preshift,0);
assert(chain[0] && chain[1] && chain[2] && chain[3]);
//
// Now link them in.
chain[0]->m_pNextRight = chain[1];
chain[1]->m_pNextRight = chain[1];
chain[0]->m_pNextDown = chain[2];
chain[1]->m_pNextDown = chain[3];
chain[2]->m_pNextRight = chain[3];
chain[2]->m_pNextDown = chain[2];
chain[3]->m_pNextRight = chain[3];
chain[3]->m_pNextDown = chain[3];
break;
default:
JPG_THROW(INVALID_PARAMETER,"PredictorBase::CreatePredictorChain",
"unable to initiate a lossless predictive scan, invalid prediction mode specified");
break;
}
}
/// Frame::StartMeasureScan
// Start a measurement scan
class Scan *Frame::StartMeasureScan(void)
{
if (m_pCurrent == NULL)
JPG_THROW(OBJECT_DOESNT_EXIST,"Frame::StartMeasureScan",
"scan parameters have not been defined yet");
if (m_pImage == NULL)
JPG_THROW(OBJECT_DOESNT_EXIST,"Frame::StartMeasureScan",
"frame is currently not available for measurements");
//
// Create a compatible image buffer and put it into BitmapCtrl,
// or re-use it.
m_pCurrent->StartMeasureScan(m_pImage);
return m_pCurrent;
}
/// RestartIntervalMarker::ParseMarker
// Parse the marker from the stream.
void RestartIntervalMarker::ParseMarker(class ByteStream *io)
{
LONG len = io->GetWord();
if (len != 4)
JPG_THROW(MALFORMED_STREAM,"RestartIntervalMarker::ParseMarker",
"DRI restart interval definition marker size is invalid");
len = io->GetWord();
if (len == ByteStream::EOF)
JPG_THROW(UNEXPECTED_EOF,"RestartIntervalMarker::ParseMarker",
"DRI restart interval definition marker run out of data");
m_usRestartInterval = UWORD(len);
}
/// NameSpace::AllocateMatrixID
// Allocate an ID for a nonlinarity.
UBYTE NameSpace::AllocateMatrixID(void) const
{
UBYTE idx = MergingSpecBox::FreeForm;
if (m_ppPrimaryList) {
const class Box *box = *m_ppPrimaryList;
while(box) {
const class MatrixBox *matrix = dynamic_cast<const MatrixBox *>(box);
if (matrix) {
if (matrix->IdOf() >= idx)
idx = matrix->IdOf() + 1;
}
box = box->NextOf();
}
}
if (m_ppSecondaryList) {
const class Box *box = *m_ppSecondaryList;
while(box) {
const class MatrixBox *matrix = dynamic_cast<const MatrixBox *>(box);
if (matrix) {
if (matrix->IdOf() >= idx)
idx = matrix->IdOf() + 1;
}
box = box->NextOf();
}
}
if (idx > 15)
JPG_THROW(OVERFLOW_PARAMETER,"NameSpace::AllocateNonlinearityID",
"cannot create more than 11 linear transformations");
return idx;
}
/// NameSpace::AllocateNonlinearityID
// Allocate an ID for a nonlinarity.
UBYTE NameSpace::AllocateNonlinearityID(void) const
{
UBYTE idx = 0;
if (m_ppPrimaryList) {
const class Box *box = *m_ppPrimaryList;
while(box) {
const class ToneMapperBox *tmo = dynamic_cast<const ToneMapperBox *>(box);
if (tmo) {
if (tmo->TableDestinationOf() >= idx)
idx = tmo->TableDestinationOf() + 1;
}
box = box->NextOf();
}
}
if (m_ppSecondaryList) {
const class Box *box = *m_ppSecondaryList;
while(box) {
const class ToneMapperBox *tmo = dynamic_cast<const ToneMapperBox *>(box);
if (tmo) {
if (tmo->TableDestinationOf() >= idx)
idx = tmo->TableDestinationOf() + 1;
}
box = box->NextOf();
}
}
if (idx > 15)
JPG_THROW(OVERFLOW_PARAMETER,"NameSpace::AllocateNonlinearityID",
"cannot create more than 16 nonlinear point transformations");
return idx;
}
/// ACRefinementScan::StartWriteScan
void ACRefinementScan::StartWriteScan(class ByteStream *io,class Checksum *chk,class BufferCtrl *ctrl)
{
#if ACCUSOFT_CODE
int i;
for(i = 0;i < m_ucCount;i++) {
m_ulX[i] = 0;
}
m_Context.Init();
assert(!ctrl->isLineBased());
m_pBlockCtrl = dynamic_cast<BlockCtrl *>(ctrl);
m_pBlockCtrl->ResetToStartOfScan(m_pScan);
//
// Actually, always:
m_bMeasure = false;
EntropyParser::StartWriteScan(io,chk,ctrl);
m_pScan->WriteMarker(io);
m_Coder.OpenForWrite(io,chk);
#else
NOREF(io);
NOREF(chk);
NOREF(ctrl);
JPG_THROW(NOT_IMPLEMENTED,"ACRefinementScan::StartWriteScan",
"Lossless JPEG not available in your code release, please contact Accusoft for a full version");
#endif
}
/// LosslessScan::StartWriteScan
void LosslessScan::StartWriteScan(class ByteStream *io,class Checksum *chk,class BufferCtrl *ctrl)
{
#if ACCUSOFT_CODE
int i;
FindComponentDimensions();
for(i = 0;i < m_ucCount;i++) {
m_pDCCoder[i] = m_pScan->DCHuffmanCoderOf(i);
m_pDCStatistics[i] = NULL;
}
assert(ctrl->isLineBased());
m_pLineCtrl = dynamic_cast<LineBuffer *>(ctrl);
m_pLineCtrl->ResetToStartOfScan(m_pScan);
EntropyParser::StartWriteScan(io,chk,ctrl);
m_pScan->WriteMarker(io);
m_Stream.OpenForWrite(io,chk);
m_bMeasure = false;
#else
NOREF(io);
NOREF(chk);
NOREF(ctrl);
JPG_THROW(NOT_IMPLEMENTED,"LosslessScan::StartWriteScan",
"Lossless JPEG not available in your code release, please contact Accusoft for a full version");
#endif
}
/// Frame::BuildImage
// Build the image buffer type fitting to the frame type.
class BitmapCtrl *Frame::BuildImage(void)
{
switch(m_Type) {
case Baseline: // also sequential
case Sequential:
case Progressive:
case ACSequential:
case ACProgressive:
{
if (m_pTables->ResidualDataOf()) {
m_pBlockHelper = new(m_pEnviron) class ResidualBlockHelper(this);
}
class BlockBitmapRequester *bb = new(m_pEnviron) class BlockBitmapRequester(this);
bb->SetBlockHelper(m_pBlockHelper);
return bb;
}
case Lossless:
case ACLossless:
case DifferentialLossless:
case ACDifferentialLossless:
case JPEG_LS:
return new(m_pEnviron) class LineBitmapRequester(this);
case Dimensions:
return new(m_pEnviron) class HierarchicalBitmapRequester(this);
default:
break; // Everything else is part of a hierarchical scan and does not have a full image buffer by itself.
}
JPG_THROW(MALFORMED_STREAM,"Frame::BuildLineAdapter","found illegal or unsupported frame type");
return NULL;
}
/// Frame::BuildLineAdapter
// Build the line adapter fitting to the frame type.
class LineAdapter *Frame::BuildLineAdapter(void)
{
switch(m_Type) {
case Baseline: // also sequential
case Sequential:
case Progressive:
case DifferentialSequential:
case DifferentialProgressive:
case ACSequential:
case ACProgressive:
case ACDifferentialSequential:
case ACDifferentialProgressive:
case Residual:
case ACResidual:
return new(m_pEnviron) class BlockLineAdapter(this); // all block based.
case Lossless:
case ACLossless:
case DifferentialLossless:
case ACDifferentialLossless:
case JPEG_LS:
return new(m_pEnviron) class LineLineAdapter(this); // all line based.
case Dimensions:
break;
}
JPG_THROW(INVALID_PARAMETER,"Frame::BuildLineAdapter","found illegal or unsupported frame type");
return NULL;
}
//
// Buffer the original data unaltered. Required for residual coding, for some modes of
// it at least.
virtual void RGB2RGB(const RectAngle<LONG> &,const struct ImageBitMap *const *,
Buffer)
{
// This does not implement residual coding, code should not go here.
JPG_THROW(INVALID_PARAMETER,"LSLosslessTrafo::RGB2RGB",
"JPEG LS lossless color transformation does not allow residual coding");
}
/// Frame::NextScan
class Scan *Frame::NextScan(void)
{
if (m_pCurrent == NULL)
JPG_THROW(OBJECT_DOESNT_EXIST,"Frame::NextScan","no scan iteration has been started, cannot advance the scan");
return m_pCurrent = m_pCurrent->NextOf();
}
/// Frame::WriteFrameType
// Write the marker that identifies this type of frame, and all the scans within it.
void Frame::WriteFrameType(class ByteStream *io) const
{
if (m_pScan == NULL)
JPG_THROW(OBJECT_DOESNT_EXIST,"Frame::WriteFrameType",
"frame parameters have not yet been installed, cannot write frame type");
m_pScan->WriteFrameType(io);
}
/// ACRefinementScan::StartMeasureScan
// Measure scan statistics.
void ACRefinementScan::StartMeasureScan(class BufferCtrl *)
{
//
// This is not required.
JPG_THROW(NOT_IMPLEMENTED,"ACRefinementScan::StartMeasureScan",
"arithmetic coding is always adaptive and does not require "
"to measure the statistics");
}
/// ACTemplate::ParseDCMarker
// Parse off DC conditioning parameters.
void ACTemplate::ParseDCMarker(class ByteStream *io)
{
LONG dc = io->Get();
UBYTE l,u;
if (dc == ByteStream::EOF)
JPG_THROW(MALFORMED_STREAM,"ACTemplate::ParseDCMarker",
"unexpected EOF while parsing off the AC conditioning parameters");
l = dc & 0x0f;
u = dc >> 4;
if (u < l)
JPG_THROW(MALFORMED_STREAM,"ACTemplate::ParseDCMarker",
"upper DC conditioning parameter must be larger or equal to the lower one");
m_ucLower = l;
m_ucUpper = u;
}
/// Thresholds::ParseMarker
// Parse the marker contents of a LSE marker.
void Thresholds::ParseMarker(class ByteStream *io,UWORD len)
{
if (len != 13)
JPG_THROW(MALFORMED_STREAM,"Thresholds::ParseMarker","LSE marker length is invalid");
m_usMaxVal = io->GetWord();
m_usT1 = io->GetWord();
m_usT2 = io->GetWord();
m_usT3 = io->GetWord();
m_usReset = io->GetWord();
}
/// Frame::FindComponent
// Find a component by a component identifier. Throws if the component does not exist.
class Component *Frame::FindComponent(UBYTE id) const
{
int i;
for(i = 0;i < m_ucDepth;i++) {
if (m_ppComponent[i]->IDOf() == id)
return m_ppComponent[i];
}
JPG_THROW(OBJECT_DOESNT_EXIST,"Frame::FindComponent","found a component ID that does not exist");
return NULL; // dummy.
}
/// EXIFMarker::ParseMarker
// Parse the adobe marker from the stream
// This will throw in case the marker is not
// recognized. The caller will have to catch
// the exception.
void EXIFMarker::ParseMarker(class ByteStream *io,UWORD len)
{
if (len < 2 + 4 + 2 + 2 + 2 + 4 + 2 + 4)
JPG_THROW(MALFORMED_STREAM,"EXIFMarker::ParseMarker","misformed EXIF marker");
//
// The exif header has already been parsed off.
len -= 2 + 4 + 2;
// Skip the rest of the marker.
if (len > 0)
io->SkipBytes(len);
}
/// EntropyParser::ParseDNLMarker
// Parse the DNL marker, update the frame height. If
// the result is true, the marker has been found.
bool EntropyParser::ParseDNLMarker(class ByteStream *io)
{
LONG dt;
if (m_bDNLFound)
return true;
dt = io->PeekWord();
while(dt == 0xffff) {
// A filler byte followed by the marker (hopefully). Skip the
// filler and try again.
io->Get();
dt = io->PeekWord();
}
if (dt == 0xffdc) {
dt = io->GetWord();
dt = io->GetWord();
if (dt != 4)
JPG_THROW(MALFORMED_STREAM,"EntropyParser::ParseDNLMarker",
"DNL marker size is out of range, must be exactly four bytes long");
dt = io->GetWord();
if (dt == ByteStream::EOF)
JPG_THROW(UNEXPECTED_EOF,"EntropyParser::ParseDNLMarker",
"stream is truncated, could not read the DNL marker");
if (dt == 0)
JPG_THROW(MALFORMED_STREAM,"EntropyParser::ParseDNLMarker",
"frame height as indicated by the DNL marker is corrupt, must be > 0");
m_pFrame->PostImageHeight(dt);
m_bDNLFound = true;
return true;
} else {
return false;
}
}
/// BitmapCtrl::RequestUserData
// Request data from the user through the indicated bitmap hook
// for the given rectangle. The rectangle is first clipped to
// range (as appropriate, if the height is already known) and
// then the desired n'th component of the scan (not the component
// index) is requested.
void BitmapCtrl::RequestUserData(class BitMapHook *bmh,const RectAngle<LONG> &r,UBYTE comp)
{
assert(comp < m_ucCount && bmh);
bmh->RequestClientData(r,m_ppBitmap[comp],m_pFrame->ComponentOf(comp));
if (m_ucPixelType == 0) { // Not yet defined
m_ucPixelType = m_ppBitmap[comp]->ibm_ucPixelType;
} else if (m_ppBitmap[comp]->ibm_ucPixelType) {
if (m_ucPixelType != m_ppBitmap[comp]->ibm_ucPixelType) {
JPG_THROW(INVALID_PARAMETER,"BitmapCtrl::RequestUserData","pixel types must be consistent accross components");
}
}
}
/// Component::ParseMarker
void Component::ParseMarker(class ByteStream *io)
{
LONG data;
data = io->Get();
if (data == ByteStream::EOF)
JPG_THROW(MALFORMED_STREAM,"Component::ParseMarker","frame marker incomplete, no component identifier found");
m_ucID = data;
data = io->Get();
if (data == ByteStream::EOF)
JPG_THROW(MALFORMED_STREAM,"Component::ParseMarker","frame marker incomplete, subsamling information missing");
m_ucMCUWidth = data >> 4;
m_ucMCUHeight = data & 0x0f;
data = io->Get();
if (data < 0 || data > 3)
JPG_THROW(MALFORMED_STREAM,"Component::ParseMarker","quantization table identifier corrupt, must be >= 0 and <= 3");
m_ucQuantTable = data;
}
/// HuffmanTemplate::BuildDecoder
// Build the huffman decoder given the template data.
void HuffmanTemplate::BuildDecoder(void)
{
class HuffmanDecoder *prev = NULL;
ULONG i,lastbits = 0;
UBYTE *values;
ULONG code = 0;
assert(m_pDecoder == NULL);
if (m_pucValues) {
// If the decoder is not used, do not build it.
assert(m_ucLengths);
for(i = 0,values = m_pucValues; i < 16U; i++) {
if (m_ucLengths[i]) {
if (values + m_ucLengths[i] > m_pucValues + m_ulCodewords)
JPG_THROW(MALFORMED_STREAM,"HuffmanTemplate::ParseMarker","Huffman table marker depends on undefined data");
// There are codes of this lengths.
code += m_ucLengths[i];
if (code >= 1UL << (i + 1))
JPG_THROW(MALFORMED_STREAM,"HuffmanTemplate::ParseMarker",
"Huffman table corrupt - entry depends on more bits than available for the bit length");
class HuffmanDecoder *huff = new(m_pEnviron) class HuffmanDecoder(values,i+1-lastbits,
m_ucLengths[i]);
if (prev) {
prev->ExtendBy(huff);
} else {
assert(m_pDecoder == NULL);
m_pDecoder = huff;
}
prev = huff;
values += m_ucLengths[i];
lastbits = i+1;
}
code <<= 1;
}
}
}
/// Frame::PostImageHeight
// Define the image size if it is not yet known here. This is
// called whenever the DNL marker is parsed in.
void Frame::PostImageHeight(ULONG height)
{
assert(height > 0 && m_pImage);
if (m_ulHeight == 0) {
m_ulHeight = height;
m_pImage->PostImageHeight(height);
} else if (m_ulHeight == height) {
JPG_WARN(MALFORMED_STREAM,"Frame::PostImageHeight",
"found a double DNL marker for a frame, frame size is known already");
} else {
JPG_THROW(MALFORMED_STREAM,"Frame::PostImageHeight",
"found a double DNL marker for a frame, indicating an inconsistent frame height");
}
}
/// ChecksumBox::ParseBoxContent
// Second level parsing stage: This is called from the first level
// parser as soon as the data is complete. Must be implemented
// by the concrete box. Returns true in case the contents is
// parsed and the stream can go away.
bool ChecksumBox::ParseBoxContent(class ByteStream *stream,UQUAD boxsize)
{
LONG pack1,pack2;
if (boxsize != 4)
JPG_THROW(MALFORMED_STREAM,"ChecksumBox::ParseBoxContent",
"Malformed JPEG stream, the checksum box size is invalid");
pack1 = stream->GetWord();
pack2 = stream->GetWord();
m_ulCheck = ULONG(pack1 << 16) | ULONG(pack2);
return true;
}