exif_reader.cpp

#include <stdlib.h>

#include <QtGlobal>
#include <QList>
#include <QDebug>
#include <QByteArray>

#include "exif_reader.h"


rint8u readByte (QFile &file)
{
  char a;
  file.getChar (&a);
  return (rint8u)a;
}


//--------------------------------------------------------------------------
// Parse the marker stream until SOS or EOI is seen;
//--------------------------------------------------------------------------
int Exif::readJpegSections (QFile &file, int *Orientation)
{
  QByteArray *data;
  rint8u a = readByte (file);

  if (a != 0xff)
      return -1;
  else
      {
       rint8u b = readByte (file);
       if (b != M_SOI) 
          return -1;
      }

    //int SectionsRead=0;
   for (;;)
       {
        int itemlen;
        int prev;
        rint8u marker = 0;
        rint8u ll, lh;

        prev = 0;
        
        for (int i = 0; ; i++)
            {
             marker = readByte (file);
             if (marker != 0xff && prev == 0xff) 
                break;
             prev = marker;
            }

        // Read the length of the section.
        lh = readByte (file);
        ll = readByte (file);
        itemlen = (lh << 8) | ll;

        if (itemlen < 2) // Invalid marker
           return -1;
           
        data = new QByteArray (file.read (itemlen - 2)); // Read the whole section.
        if (data->isEmpty()) 
           return -1; // Could not allocate memory

        if(data->size() != itemlen - 2) 
           return -1; // Premature end of file?

        switch (marker)
               {
                case M_SOS:   // stop before hitting compressed data
                           return 0;

                case M_EOI:   // in case it's a tables-only JPEG stream
                           return -1;

                case M_COM: // Comment section
                            delete (data);
                            break;

                case M_JFIF:
                            // Regular jpegs always have this tag, exif images have the exif
                            // marker instead, althogh ACDsee will write images with both markers.
                            // this program will re-create this marker on absence of exif marker.
                            // hence no need to keep the copy from the file.
                            if (itemlen >= 16){ // if Jfif header not too short
                                               // skipped
                                              }

                            delete (data);
                            break;

                case M_EXIF:
                             // There can be different section using the same marker.
                            if (data->left(4) == "Exif")
                               {
                                processEXIF (data, itemlen, Orientation);
                                break;
                               }
                            // Oterwise, discard this section.
                            delete (data);
                            break;

                case M_IPTC:
                            delete (data);
                            break;

               default:
                    // Skip any other sections.
                    break;

        } // switch


    } // for(;;)

    return 0;
}


// Convert a 16 bit unsigned value from file's native byte order
int Get16u (const void * Short, int MotorolaOrder)
{
     if (MotorolaOrder)
        return (((uchar *)Short)[0] << 8) | ((uchar *)Short)[1];
     else
        return (((uchar *)Short)[1] << 8) | ((uchar *)Short)[0];
}


// Convert a 32 bit signed value from file's native byte order
int Get32s(const void * Long, int MotorolaOrder)
{
  if (MotorolaOrder)
     return  ((( char *)Long)[0] << 24) | (((uchar *)Long)[1] << 16)
             | (((uchar *)Long)[2] << 8 ) | (((uchar *)Long)[3] << 0 );
  else
      return  ((( char *)Long)[3] << 24) | (((uchar *)Long)[2] << 16)
              | (((uchar *)Long)[1] << 8 ) | (((uchar *)Long)[0] << 0 );
}

// Convert a 32 bit unsigned value from file's native byte order
unsigned Get32u (const void * Long, int MotorolaOrder)
{
  return (unsigned)Get32s(Long, MotorolaOrder) & 0xffffffff;
}

#define NUM_FORMATS 12
#define FMT_BYTE       1
#define FMT_STRING     2
#define FMT_USHORT     3
#define FMT_ULONG      4
#define FMT_URATIONAL  5
#define FMT_SBYTE      6
#define FMT_UNDEFINED  7
#define FMT_SSHORT     8
#define FMT_SLONG      9
#define FMT_SRATIONAL 10
#define FMT_SINGLE    11
#define FMT_DOUBLE    12


// Evaluate number, be it int, rational, or float from directory.
double ConvertAnyFormat (const void * ValuePtr, int Format, int MotorolaOrder)
{
  double Value = 0.0;

  switch (Format)
         {
          case FMT_SBYTE:     Value = *(signed char *)ValuePtr;
                              break;

          case FMT_BYTE:      Value = *(uchar *)ValuePtr;
                              break;

          case FMT_USHORT:    Value = Get16u(ValuePtr, MotorolaOrder);          break;
          case FMT_ULONG:     Value = Get32u(ValuePtr, MotorolaOrder);          break;

          case FMT_URATIONAL:
          case FMT_SRATIONAL:
                             {
                              int Num = Get32s(ValuePtr, MotorolaOrder);
                              int Den = Get32s(4+(char *)ValuePtr, MotorolaOrder);
                              if (Den == 0)
                                  Value = 0;
                              else
                                  Value = (double) Num / Den;

                              break;
                             }

         case FMT_SSHORT:    Value = (signed short)Get16u(ValuePtr, MotorolaOrder);
                             break;

         case FMT_SLONG:     Value = Get32s(ValuePtr, MotorolaOrder);
                             break;

         // Not sure if this is correct (never seen float used in Exif format)
         case FMT_SINGLE:    Value = (double)*(float *)ValuePtr;
                             break;

         case FMT_DOUBLE:    Value = *(double *)ValuePtr;
                            break;

         default: Value = 100;// Illegal format code
        }

  return Value;
}



#define TAG_ORIENTATION        0x0112
#define TAG_INTEROP_OFFSET     0xA005
#define TAG_EXIF_OFFSET        0x8769
#define DIR_ENTRY_ADDR(Start, Entry) (Start+2+12*(Entry))

const int BytesPerFormat[] = {0,1,1,2,4,8,1,1,2,4,8,4,8};


// Process one of the nested EXIF directories.
int Exif::processEXIFDir (const char *DirStart, const char *OffsetBase, rint32u exifSize, rint32u nesting, int MotorolaOrder, int *NumOrientations, int *Orientation)
{
  int numDirEntries;

  if(nesting > 4)
    return -1; // Maximum Exif directory nesting exceeded (corrupt Exif header)

  numDirEntries = Get16u (DirStart, MotorolaOrder);
    //qDebug() << "num entries: " << numDirEntries;


  for (int de=0; de<numDirEntries; de++)
      {
       const char *ValuePtr;

       //const char *DirEntry = DIR_ENTRY_ADDR(DirStart, de);
       const char *DirEntry = DirStart + 2 + (12 * de);

       int Tag        = Get16u(DirEntry,   MotorolaOrder);
       int Format     = Get16u(DirEntry+2, MotorolaOrder);
       int Components = Get32u(DirEntry+4, MotorolaOrder);
        //qDebug() << "tag:" << Tag << "format:" << Format << "components:" << Components;

       if (Format-1 >= NUM_FORMATS)
           continue; // (-1) catches illegal zero case as unsigned underflows to positive large.

       if ((unsigned)Components > 0x10000)
           continue; // Too many components

        int ByteCount = Components * BytesPerFormat[Format];
        //qDebug() << "byte count" << ByteCount;

        if (ByteCount > 4)
           { // If its bigger than 4 bytes, the dir entry contains an offset.
            unsigned OffsetVal = Get32u (DirEntry + 8, MotorolaOrder);

            if (OffsetVal+ByteCount > exifSize)
               continue; // Bogus pointer offset and / or bytecount value

             ValuePtr = OffsetBase + OffsetVal;
           }
        else // 4 bytes or less and value is in the dir entry itself
            ValuePtr = DirEntry+8;



        // Extract useful components of tag
        switch (Tag) {
                      case TAG_ORIENTATION:
                                           if (*NumOrientations >= 2)
                            // Can have another orientation tag for the thumbnail, but if there's
                            // a third one, things are stringae.
                                              break;


                                           if (*NumOrientations == 0)
                                              *Orientation = (int)ConvertAnyFormat(ValuePtr, Format, MotorolaOrder);
                    //qDebug() << "orientation:" << *Orientation;

                                           if (*Orientation < 0 || *Orientation > 8)
                                  // Undefined rotation value
                                               *Orientation = 0;

                                           *NumOrientations += 1;
                                           break;

                       case TAG_EXIF_OFFSET:

                       case TAG_INTEROP_OFFSET:
                                                const char *SubdirStart = OffsetBase + Get32u(ValuePtr, MotorolaOrder);
                                                if (SubdirStart < OffsetBase || SubdirStart > OffsetBase+ exifSize)
                                                   ;                    // Illegal Exif or interop ofset directory link
                                                else
                                                    processEXIFDir (SubdirStart, OffsetBase, exifSize, nesting+ 1, MotorolaOrder, NumOrientations, Orientation);

        }
    }

    return 0;
}


// Process a EXIF marker
// Describes all the drivel that most digital cameras include...
int Exif::processEXIF(QByteArray *data, int itemlen, int *Orientation)
{
  int MotorolaOrder = 0;

   // Check the EXIF header component
  if (data->left(6) == "Exif\0\0")
      qDebug() << data->left(4);


  if(data->mid(6,2) == "II") // Exif section in Intel order
     //qDebug() << data->mid(6,2);
     MotorolaOrder = 0;
  else
      {
       if(data->mid(6,2) == "II") // Exif section in Motorola order
         //qDebug() << data->mid(6,2);
         MotorolaOrder = 1;
       else
           return -1; // Invalid Exif alignment marker.
      }

    // get first offset
  QByteArray ttt (data->mid (10, 4));
  const char *ttt2 = ttt.constData();
  rint32u FirstOffset = Get32u (ttt2, MotorolaOrder);
    //qDebug() << "fist offset: " << FirstOffset;
  if (FirstOffset < 8 || FirstOffset > 16)
     if (FirstOffset < 16 || int (FirstOffset) > itemlen - 16)
         return -1;  // invalid offset for first Exif IFD value ;


  const char *dirStart = data->constData();
  const char *offsetBase = data->constData();

  dirStart   += 6 + FirstOffset;
  offsetBase += 6;
  int numOrientations = 0;
    // First directory starts 16 bytes in.  All offset are relative to 8 bytes in.
  processEXIFDir (dirStart, offsetBase, itemlen - 8, 0, MotorolaOrder, &numOrientations, Orientation);
    //qDebug() << "num orientations:" << numOrientations;

  return 0;
}


int Exif::readJpegFile (QFile &file, int *Orientation)
{
  readJpegSections (file, Orientation);
  return 0;
}


int Exif::getExifOrientation (QFile &file)
{
  int r = 0;
  readJpegFile (file, &r);
  return r;
}


int get_exif_orientation (const QString &fname)
{
  Exif exif;
  int o = 0;
  QFile file (fname);
  if (file.open(QIODevice::ReadOnly))
     {
      o = exif.getExifOrientation(file/*, &o*/);
      file.close();
     }
     
  return o;    
}