gdcmdocument.cxx

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      // 0xffff means that we deal with 'No Length' Sequence 
      //        or 'No Length' SQItem
      if ( length16 == 0xffff) 
      {           
         length16 = 0;
      }
      FixDocEntryFoundLength( entry, (uint32_t)length16 );
      return;
   }
   else
   {
      // Either implicit VR or a non DICOM conformal (see note 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.

     // Well ... group 0002 is always coded in 'Explicit VR Litle Endian'
     // even if Transfer Syntax is 'Implicit VR ...'
     // --> Except for 'Implicit VR Big Endian Transfer Syntax GE Private' 

      FixDocEntryFoundLength( entry, ReadInt32() );
      return;
   }
}

/**
 * \brief  Find the Length till the next sequence delimiter
 * \warning NOT end user intended method !
 * @return 
 */
uint32_t Document::FindDocEntryLengthOBOrOW()
   throw( FormatUnexpected )
{
   // See PS 3.5-2001, section A.4 p. 49 on encapsulation of encoded pixel data.
   long positionOnEntry = Fp->tellg(); // Only for OB,OW DataElements

   bool foundSequenceDelimiter = false;
   uint32_t totalLength = 0;

   while ( !foundSequenceDelimiter )
   {
      uint16_t group;
      uint16_t elem;
      try
      {
         group = ReadInt16();
         elem  = ReadInt16();   
      }
      catch ( FormatError )
      {
         throw FormatError("Unexpected end of file encountered during ",
                           "Document::FindDocEntryLengthOBOrOW()");
      }
      // We have to decount the group and element we just read
      totalLength += 4;     
      if ( group != 0xfffe || ( ( elem != 0xe0dd ) && ( elem != 0xe000 ) ) )
      {
         gdcmWarningMacro( 
              "Neither an Item tag nor a Sequence delimiter tag on :" 
           << std::hex << group << " , " << elem 
           << ")" );
  
         Fp->seekg(positionOnEntry, std::ios::beg); // Once per fragment (if any) of OB,OW DataElements
         throw FormatUnexpected( 
               "Neither an Item tag nor a Sequence delimiter tag.");
      }
      if ( elem == 0xe0dd )
      {
         foundSequenceDelimiter = true;
      }
      uint32_t itemLength = ReadInt32();
      // We add 4 bytes since we just read the ItemLength with ReadInt32
      totalLength += itemLength + 4;
      SkipBytes(itemLength);
      
      if ( foundSequenceDelimiter )
      {
         break;
      }
   }
   Fp->seekg( positionOnEntry, std::ios::beg); // Only for OB,OW DataElements
   return totalLength;
}

/**
 * \brief     Find the Value Representation of the current Dicom Element.
 * @return    Value Representation of the current Entry
 */
std::string Document::FindDocEntryVR()
{
   if ( Filetype != ExplicitVR )
      return GDCM_UNKNOWN;

   long positionOnEntry = Fp->tellg();
   // Warning: we believe this is explicit VR (Value Representation) because
   // we used a heuristic that found "UL" in the first tag. Alas this
   // doesn't guarantee that all the tags will be in explicit VR. In some
   // cases (see e-film filtered files) one finds implicit VR tags mixed
   // within an explicit VR file. Hence we make sure the present tag
   // is in explicit VR and try to fix things if it happens not to be
   // the case.

   char vr[3];
   Fp->read (vr, (size_t)2);
   vr[2] = 0;

   if ( !CheckDocEntryVR(vr) )
   {
      Fp->seekg(positionOnEntry, std::ios::beg);
      return GDCM_UNKNOWN;
   }
   return vr;
}

/**
 * \brief     Check the correspondance between the VR of the header entry
 *            and the taken VR. If they are different, the header entry is 
 *            updated with the new VR.
 * @param     vr    Dicom Value Representation
 * @return    false if the VR is incorrect or if the VR isn't referenced
 *            otherwise, it returns true
*/
bool Document::CheckDocEntryVR(VRKey vr)
{
   if ( !Global::GetVR()->IsValidVR(vr) )
      return false;

   return true; 
}

/**
 * \brief   Get the transformed value of the header entry. The VR value 
 *          is used to define the transformation to operate on the value
 * \warning NOT end user intended method !
 * @param   entry entry to tranform
 * @return  Transformed entry value
 */
std::string Document::GetDocEntryValue(DocEntry *entry)
{
   if ( IsDocEntryAnInteger(entry) && entry->IsImplicitVR() )
   {
      std::string val = ((ValEntry *)entry)->GetValue();
      std::string vr  = entry->GetVR();
      uint32_t length = entry->GetLength();
      itksys_ios::ostringstream s;
      int nbInt;

      // When short integer(s) are expected, read and convert the following
      // n * 2 bytes properly i.e. as a multivaluated strings
      // (each single value is separated fromthe next one by '\'
      // as usual for standard multivaluated filels
      // Elements with Value Multiplicity > 1
      // contain a set of short integers (not a single one) 
   
      if ( vr == "US" || vr == "SS" )
      {
         uint16_t newInt16;

         nbInt = length / 2;
         for (int i=0; i < nbInt; i++) 
         {
            if ( i != 0 )
            {
               s << '\\';
            }
            newInt16 = ( val[2*i+0] & 0xFF ) + ( ( val[2*i+1] & 0xFF ) << 8);
            newInt16 = SwapShort( newInt16 );
            s << newInt16;
         }
      }

      // When integer(s) are expected, read and convert the following 
      // n * 4 bytes properly i.e. as a multivaluated strings
      // (each single value is separated fromthe next one by '\'
      // as usual for standard multivaluated filels
      // Elements with Value Multiplicity > 1
      // contain a set of integers (not a single one) 
      else if ( vr == "UL" || vr == "SL" )
      {
         uint32_t newInt32;

         nbInt = length / 4;
         for (int i=0; i < nbInt; i++) 
         {
            if ( i != 0)
            {
               s << '\\';
            }
            newInt32 = ( val[4*i+0] & 0xFF )
                    + (( val[4*i+1] & 0xFF ) <<  8 )
                    + (( val[4*i+2] & 0xFF ) << 16 )
                    + (( val[4*i+3] & 0xFF ) << 24 );
            newInt32 = SwapLong( newInt32 );
            s << newInt32;
         }
      }
#ifdef GDCM_NO_ANSI_STRING_STREAM
      s << std::ends; // to avoid oddities on Solaris
#endif //GDCM_NO_ANSI_STRING_STREAM
      return s.str();
   }
   return ((ValEntry *)entry)->GetValue();
}

/**
 * \brief   Get the reverse transformed value of the header entry. The VR 
 *          value is used to define the reverse transformation to operate on
 *          the value
 * \warning NOT end user intended method !
 * @param   entry Entry to reverse transform
 * @return  Reverse transformed entry value
 */
std::string Document::GetDocEntryUnvalue(DocEntry *entry)
{
   if ( IsDocEntryAnInteger(entry) && entry->IsImplicitVR() )
   {
      std::string vr = entry->GetVR();
      std::vector<std::string> tokens;
      itksys_ios::ostringstream s;

      if ( vr == "US" || vr == "SS" )
      {
         uint16_t newInt16;

         tokens.erase( tokens.begin(), tokens.end()); // clean any previous value
         Util::Tokenize (((ValEntry *)entry)->GetValue(), tokens, "\\");
         for (unsigned int i=0; i<tokens.size(); i++) 
         {
            newInt16 = atoi(tokens[i].c_str());
            s << (  newInt16        & 0xFF ) 
              << (( newInt16 >> 8 ) & 0xFF );
         }
         tokens.clear();
      }
      if ( vr == "UL" || vr == "SL")
      {
         uint32_t newInt32;

         tokens.erase(tokens.begin(),tokens.end()); // clean any previous value
         Util::Tokenize (((ValEntry *)entry)->GetValue(), tokens, "\\");
         for (unsigned int i=0; i<tokens.size();i++) 
         {
            newInt32 = atoi(tokens[i].c_str());
            s << (char)(  newInt32         & 0xFF ) 
              << (char)(( newInt32 >>  8 ) & 0xFF )
              << (char)(( newInt32 >> 16 ) & 0xFF )
              << (char)(( newInt32 >> 24 ) & 0xFF );
         }
         tokens.clear();
      }

#ifdef GDCM_NO_ANSI_STRING_STREAM
      s << std::ends; // to avoid oddities on Solaris
#endif //GDCM_NO_ANSI_STRING_STREAM
      return s.str();
   }

   return ((ValEntry *)entry)->GetValue();
}

/**
 * \brief   Skip a given Header Entry 
 * \warning NOT end user intended method !
 * @param   entry entry to skip
 */
void Document::SkipDocEntry(DocEntry *entry) 
{
   SkipBytes(entry->GetLength());
}

/**
 * \brief   Skips to the beginning of the next Header Entry 
 * \warning NOT end user intended method !
 * @param   currentDocEntry entry to skip
 */
void Document::SkipToNextDocEntry(DocEntry *currentDocEntry) 
{
   long l = currentDocEntry->GetReadLength();
   if ( (uint32_t)l == (uint32_t)-1 ) // length = 0xffff shouldn't appear here ...
                  // ... but PMS imagers happen !
      return;
   Fp->seekg((size_t)(currentDocEntry->GetOffset()), std::ios::beg); //FIXME :each DocEntry
   if (currentDocEntry->GetGroup() != 0xfffe)  // for fffe pb
   {
      Fp->seekg( l,std::ios::cur);                                 //FIXME :each DocEntry
   }
}

/**
 * \brief   When the length of an element value is obviously wrong (because
 *          the parser went Jabberwocky) one can hope improving things by
 *          applying some heuristics.
 * @param   entry entry to check
 * @param   foundLength first assumption about length    
 */
void Document::FixDocEntryFoundLength(DocEntry *entry,
                                      uint32_t foundLength)
{
   entry->SetReadLength( foundLength );// will be updated only if a bug is found
   if ( foundLength == 0xffffffff)
   {
      foundLength = 0;
   }
   
   uint16_t gr   = entry->GetGroup();
   uint16_t elem = entry->GetElement(); 
     
   if ( foundLength % 2)
   {
      gdcmWarningMacro( "Warning : Tag with uneven length " << foundLength
        <<  " in x(" << std::hex << gr << "," << elem <<")");
   }
      
   //////// Fix for some naughty General Electric images.
   // Allthough not recent many such GE corrupted images are still present
   // on Creatis hard disks. Hence this fix shall remain when such images
   // are no longer in use (we are talking a few years, here)...
   // Note: XMedCon probably uses such a trick since it is able to read
   //       those pesky GE images ...
   if ( foundLength == 13)
   {
      // Only happens for this length !
      if ( gr != 0x0008 || ( elem != 0x0070 && elem != 0x0080 ) )
      {
         foundLength = 10;
         entry->SetReadLength(10); // a bug is to be fixed !?
      }
   }

   //////// Fix for some brain-dead 'Leonardo' Siemens images.
   // Occurence of such images is quite low (unless one leaves close to a
   // 'Leonardo' source. Hence, one might consider commenting out the
   // following fix on efficiency reasons.
   else if ( gr == 0x0009 && ( elem == 0x1113 || elem == 0x1114 ) )
   {
      // Ideally we should check we are in Explicit and double check
      // that VR=UL... this is done properly in gdcm2
      if( foundLength == 6 )
      {
         gdcmWarningMacro( "Replacing Length from 6 into 4" );
         foundLength = 4;
         entry->SetReadLength(4); // a bug is to be fixed !
      }
      else if ( foundLength%4 )
      {
         gdcmErrorMacro( "This looks like to a buggy Siemens DICOM file."
          "The length of this tag seems to be wrong" );
      }
   } 
 
   else if ( entry->GetVR() == "SQ" )
   {
      foundLength = 0;      // ReadLength is unchanged 
   } 
    
   //////// We encountered a 'delimiter' element i.e. a tag of the form 
   // "fffe|xxxx" which is just a marker. Delimiters length should not be
   // taken into account.
   else if ( gr == 0xfffe )
   {    
     // According to the norm, fffe|0000 shouldn't exist. BUT the Philips
     // image gdcmData/gdcm-MR-PHILIPS-16-Multi-Seq.dcm happens to
     // causes extra troubles...
     if ( entry->GetElement() != 0x0000 )
     {
        foundLength = 0;
     }
   }
   entry->SetLength(foundLength);
}

/**
 * \brief   Apply some heuristics to predict whether the considered 
 *          element value contains/represents an integer or not.
 * @param   entry The element value on which to apply the predicate.
 * @return  The result of the heuristical predicate.
 */
bool Document::IsDocEntryAnInteger(DocEntry *entry)
{
   uint16_t elem         = entry->GetElement();
   uint16_t group        = entry->GetGroup();
   (void)group;
   const std::string &vr = entry->GetVR();
   uint32_t length       = entry->GetLength();

   // When we have some semantics on the element we just read, and if we
   // a priori know we are dealing with an integer, then we shall be
   // able to swap it's element value properly.
   if ( elem == 0 )  // This is the group length of the group
   {  
      if ( length == 4 )
      {
         return true;
      }
      else 
      {
         // Although this should never happen, still some images have a
         // corrupted group length [e.g. have a glance at offset x(8336) of
         // gdcmData/gdcm-MR-PHILIPS-16-Multi-Seq.dcm.
         // Since for dicom compliant and well behaved headers, the present
         // test is useless (and might even look a bit paranoid), when we
         // encounter such an ill-formed image, we simply display a warning
         // message and proceed on parsing (while crossing fingers).
         long filePosition = Fp->tellg(); // Only when elem 0x0000 length is not 4 (?!?)
         (void)filePosition;
         gdcmWarningMacro( "Erroneous Group Length element length  on : ("