-
-
-void gdcmHeader::FixFoundLength(ElValue * ElVal, guint32 FoundLength) {
- // Heuristic: a final fix.
- if ( FoundLength == 0xffffffff)
- FoundLength = 0;
- ElVal->SetLength(FoundLength);
-}
-
-guint32 gdcmHeader::FindLengthOB(void) {
- // See PS 3.5-2001, section A.4 p. 49 on encapsulation of encoded pixel data.
- guint16 g;
- guint16 n;
- long PositionOnEntry = ftell(fp);
- bool FoundSequenceDelimiter = false;
- guint32 TotalLength = 0;
- guint32 ItemLength;
-
- while ( ! FoundSequenceDelimiter) {
- g = ReadInt16();
- n = ReadInt16();
- TotalLength += 4; // We even have to decount the group and element
- if ( g != 0xfffe ) {
- dbg.Verbose(1, "gdcmHeader::FindLengthOB: ",
- "wrong group for an item sequence.");
- throw Error::FileReadError(fp, "gdcmHeader::FindLengthOB");
- }
- if ( n == 0xe0dd )
- FoundSequenceDelimiter = true;
- else if ( n != 0xe000) {
- dbg.Verbose(1, "gdcmHeader::FindLengthOB: ",
- "wrong element for an item sequence.");
- throw Error::FileReadError(fp, "gdcmHeader::FindLengthOB");
- }
- ItemLength = ReadInt32();
- TotalLength += ItemLength + 4; // We add 4 bytes since we just read
- // the ItemLength with ReadInt32
- SkipBytes(ItemLength);
- }
- fseek(fp, PositionOnEntry, SEEK_SET);
- return TotalLength;
-}
-
-void gdcmHeader::FindLength(ElValue * ElVal) {
- guint16 element = ElVal->GetElement();
- string vr = ElVal->GetVR();
- guint16 length16;
-
- if ( (filetype == ExplicitVR) && ! ElVal->IsImplicitVr() ) {
-
- if ( (vr=="OB") || (vr=="OW") || (vr=="SQ") || (vr=="UN") ) {
- // The following reserved two bytes (see PS 3.5-2001, section
- // 7.1.2 Data element structure with explicit vr p27) must be
- // skipped before proceeding on reading the length on 4 bytes.
- fseek(fp, 2L, SEEK_CUR);
- guint32 length32 = ReadInt32();
- if ( (vr == "OB") && (length32 == 0xffffffff) ) {
- ElVal->SetLength(FindLengthOB());
- return;
- }
- FixFoundLength(ElVal, length32);
- return;
- }
-
- // Length is encoded on 2 bytes.
- length16 = ReadInt16();
-
- // We can tell the current file is encoded in big endian (like
- // Data/US-RGB-8-epicard) when we find the "Transfer Syntax" tag
- // and it's value is the one of the encoding of a big endian file.
- // In order to deal with such big endian encoded files, we have
- // (at least) two strategies:
- // * when we load the "Transfer Syntax" tag with value of big endian
- // encoding, we raise the proper flags. Then we wait for the end
- // of the META group (0x0002) among which is "Transfer Syntax",
- // before switching the swap code to big endian. We have to postpone
- // the switching of the swap code since the META group is fully encoded
- // in little endian, and big endian coding only starts at the next
- // group. The corresponding code can be hard to analyse and adds
- // many additional unnecessary tests for regular tags.
- // * the second strategy consist in waiting for trouble, that shall appear
- // when we find the first group with big endian encoding. This is
- // easy to detect since the length of a "Group Length" tag (the
- // ones with zero as element number) has to be of 4 (0x0004). When we
- // encouter 1024 (0x0400) chances are the encoding changed and we
- // found a group with big endian encoding.
- // We shall use this second strategy. In order make sure that we
- // can interpret the presence of an apparently big endian encoded
- // length of a "Group Length" without committing a big mistake, we
- // add an additional check: we look in the allready parsed elements
- // for the presence of a "Transfer Syntax" whose value has to be "big
- // endian encoding". When this is the case, chances are we got our
- // hands on a big endian encoded file: we switch the swap code to
- // big endian and proceed...
- if ( (element == 0x000) && (length16 == 0x0400) ) {
- if ( ! IsExplicitVRBigEndianTransferSyntax() )
- throw Error::FileReadError(fp, "gdcmHeader::FindLength");
- length16 = 4;
- SwitchSwapToBigEndian();
- // Restore the unproperly loaded values i.e. the group, the element
- // and the dictionary entry depending on them.
- guint16 CorrectGroup = SwapShort(ElVal->GetGroup());
- guint16 CorrectElem = SwapShort(ElVal->GetElement());
- gdcmDictEntry * NewTag = IsInDicts(CorrectGroup, CorrectElem);
- if (!NewTag) {
- // This correct tag is not in the dictionary. Create a new one.
- NewTag = new gdcmDictEntry(CorrectGroup, CorrectElem);
- }
- // FIXME this can create a memory leaks on the old entry that be
- // left unreferenced.
- ElVal->SetDictEntry(NewTag);
- }
-
- // Heuristic: well some files are really ill-formed.
- if ( length16 == 0xffff) {
- length16 = 0;
- dbg.Verbose(0, "gdcmHeader::FindLength",
- "Erroneous element length fixed.");
- }
- FixFoundLength(ElVal, (guint32)length16);
- return;
- }
-
- // Either implicit VR or a non DICOM conformal (see not below) explicit
- // VR that ommited the VR of (at least) this element. Farts happen.
- // [Note: according to the part 5, PS 3.5-2001, section 7.1 p25
- // on Data elements "Implicit and Explicit VR Data Elements shall
- // not coexist in a Data Set and Data Sets nested within it".]
- // Length is on 4 bytes.
- FixFoundLength(ElVal, ReadInt32());
-}