//--------------------------------------------------------------------------
// Program to pull the information out of various types of EFIF digital
// camera files and show it in a reasonably consistent way
//
// This module parses the very complicated exif structures.
//
// Matthias Wandel,  Dec 1999 - August 2000
//--------------------------------------------------------------------------


#include "exif.h"
#include <qwmatrix.h>
#include <kglobal.h>


static unsigned char * LastExifRefd;
static int ExifSettingsLength;
static double FocalplaneXRes;
static double FocalplaneUnits;
static int MotorolaOrder = 0;
static int SectionsRead;
//static int HaveAll;

//--------------------------------------------------------------------------
// Table of Jpeg encoding process names

#define M_SOF0  0xC0            // Start Of Frame N
#define M_SOF1  0xC1            // N indicates which compression process
#define M_SOF2  0xC2            // Only SOF0-SOF2 are now in common use
#define M_SOF3  0xC3
#define M_SOF5  0xC5            // NB: codes C4 and CC are NOT SOF markers
#define M_SOF6  0xC6
#define M_SOF7  0xC7
#define M_SOF9  0xC9
#define M_SOF10 0xCA
#define M_SOF11 0xCB
#define M_SOF13 0xCD
#define M_SOF14 0xCE
#define M_SOF15 0xCF
#define M_SOI   0xD8            // Start Of Image (beginning of datastream)
#define M_EOI   0xD9            // End Of Image (end of datastream)
#define M_SOS   0xDA            // Start Of Scan (begins compressed data)
#define M_JFIF  0xE0            // Jfif marker
#define M_EXIF  0xE1            // Exif marker
#define M_COM   0xFE            // COMment


TagTable_t ProcessTable[] = {
    { M_SOF0,   "Baseline"},
    { M_SOF1,   "Extended sequential"},
    { M_SOF2,   "Progressive"},
    { M_SOF3,   "Lossless"},
    { M_SOF5,   "Differential sequential"},
    { M_SOF6,   "Differential progressive"},
    { M_SOF7,   "Differential lossless"},
    { M_SOF9,   "Extended sequential, arithmetic coding"},
    { M_SOF10,  "Progressive, arithmetic coding"},
    { M_SOF11,  "Lossless, arithmetic coding"},
    { M_SOF13,  "Differential sequential, arithmetic coding"},
    { M_SOF14,  "Differential progressive, arithmetic coding"},
    { M_SOF15,  "Differential lossless, arithmetic coding"},
    { 0,        "Unknown"}
};



//--------------------------------------------------------------------------
// Describes format descriptor
static int BytesPerFormat[] = {0,1,1,2,4,8,1,1,2,4,8,4,8};
#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

//--------------------------------------------------------------------------
// Describes tag values

#define TAG_EXIF_OFFSET       0x8769
#define TAG_INTEROP_OFFSET    0xa005

#define TAG_MAKE              0x010F
#define TAG_MODEL             0x0110
#define TAG_ORIENTATION       0x0112

#define TAG_EXPOSURETIME      0x829A
#define TAG_FNUMBER           0x829D

#define TAG_SHUTTERSPEED      0x9201
#define TAG_APERTURE          0x9202
#define TAG_MAXAPERTURE       0x9205
#define TAG_FOCALLENGTH       0x920A

#define TAG_DATETIME_ORIGINAL 0x9003
#define TAG_USERCOMMENT       0x9286

#define TAG_SUBJECT_DISTANCE  0x9206
#define TAG_FLASH             0x9209

#define TAG_FOCALPLANEXRES    0xa20E
#define TAG_FOCALPLANEUNITS   0xa210
#define TAG_EXIF_IMAGEWIDTH   0xA002
#define TAG_EXIF_IMAGELENGTH  0xA003

// the following is added 05-jan-2001 vcs
#define TAG_EXPOSURE_BIAS     0x9204
#define TAG_WHITEBALANCE      0x9208
#define TAG_METERING_MODE     0x9207
#define TAG_EXPOSURE_PROGRAM  0x8822
#define TAG_ISO_EQUIVALENT    0x8827
#define TAG_COMPRESSION_LEVEL 0x9102

#define TAG_THUMBNAIL_OFFSET  0x0201
#define TAG_THUMBNAIL_LENGTH  0x0202


/*static TagTable_t TagTable[] = {
  {   0x100,   "ImageWidth"},
  {   0x101,   "ImageLength"},
  {   0x102,   "BitsPerSample"},
  {   0x103,   "Compression"},
  {   0x106,   "PhotometricInterpretation"},
  {   0x10A,   "FillOrder"},
  {   0x10D,   "DocumentName"},
  {   0x10E,   "ImageDescription"},
  {   0x10F,   "Make"},
  {   0x110,   "Model"},
  {   0x111,   "StripOffsets"},
  {   0x112,   "Orientation"},
  {   0x115,   "SamplesPerPixel"},
  {   0x116,   "RowsPerStrip"},
  {   0x117,   "StripByteCounts"},
  {   0x11A,   "XResolution"},
  {   0x11B,   "YResolution"},
  {   0x11C,   "PlanarConfiguration"},
  {   0x128,   "ResolutionUnit"},
  {   0x12D,   "TransferFunction"},
  {   0x131,   "Software"},
  {   0x132,   "DateTime"},
  {   0x13B,   "Artist"},
  {   0x13E,   "WhitePoint"},
  {   0x13F,   "PrimaryChromaticities"},
  {   0x156,   "TransferRange"},
  {   0x200,   "JPEGProc"},
  {   0x201,   "ThumbnailOffset"},
  {   0x202,   "ThumbnailLength"},
  {   0x211,   "YCbCrCoefficients"},
  {   0x212,   "YCbCrSubSampling"},
  {   0x213,   "YCbCrPositioning"},
  {   0x214,   "ReferenceBlackWhite"},
  {   0x828D,  "CFARepeatPatternDim"},
  {   0x828E,  "CFAPattern"},
  {   0x828F,  "BatteryLevel"},
  {   0x8298,  "Copyright"},
  {   0x829A,  "ExposureTime"},
  {   0x829D,  "FNumber"},
  {   0x83BB,  "IPTC/NAA"},
  {   0x8769,  "ExifOffset"},
  {   0x8773,  "InterColorProfile"},
  {   0x8822,  "ExposureProgram"},
  {   0x8824,  "SpectralSensitivity"},
  {   0x8825,  "GPSInfo"},
  {   0x8827,  "ISOSpeedRatings"},
  {   0x8828,  "OECF"},
  {   0x9000,  "ExifVersion"},
  {   0x9003,  "DateTimeOriginal"},
  {   0x9004,  "DateTimeDigitized"},
  {   0x9101,  "ComponentsConfiguration"},
  {   0x9102,  "CompressedBitsPerPixel"},
  {   0x9201,  "ShutterSpeedValue"},
  {   0x9202,  "ApertureValue"},
  {   0x9203,  "BrightnessValue"},
  {   0x9204,  "ExposureBiasValue"},
  {   0x9205,  "MaxApertureValue"},
  {   0x9206,  "SubjectDistance"},
  {   0x9207,  "MeteringMode"},
  {   0x9208,  "LightSource"},
  {   0x9209,  "Flash"},
  {   0x920A,  "FocalLength"},
  {   0x927C,  "MakerNote"},
  {   0x9286,  "UserComment"},
  {   0x9290,  "SubSecTime"},
  {   0x9291,  "SubSecTimeOriginal"},
  {   0x9292,  "SubSecTimeDigitized"},
  {   0xA000,  "FlashPixVersion"},
  {   0xA001,  "ColorSpace"},
  {   0xA002,  "ExifImageWidth"},
  {   0xA003,  "ExifImageLength"},
  {   0xA005,  "InteroperabilityOffset"},
  {   0xA20B,  "FlashEnergy"},                 // 0x920B in TIFF/EP
  {   0xA20C,  "SpatialFrequencyResponse"},  // 0x920C    -  -
  {   0xA20E,  "FocalPlaneXResolution"},     // 0x920E    -  -
  {   0xA20F,  "FocalPlaneYResolution"},      // 0x920F    -  -
  {   0xA210,  "FocalPlaneResolutionUnit"},  // 0x9210    -  -
  {   0xA214,  "SubjectLocation"},             // 0x9214    -  -
  {   0xA215,  "ExposureIndex"},            // 0x9215    -  -
  {   0xA217,  "SensingMethod"},            // 0x9217    -  -
  {   0xA300,  "FileSource"},
  {   0xA301,  "SceneType"},
  {      0, NULL}
} ;
*/


//--------------------------------------------------------------------------
// Parse the marker stream until SOS or EOI is seen;
//--------------------------------------------------------------------------
int ExifData::ReadJpegSections (QFile & infile, ReadMode_t ReadMode)
{
    int a;

    a = infile.getch();

    if (a != 0xff || infile.getch() != M_SOI) {
        SectionsRead = 0;
        return false;
    }
    for(SectionsRead = 0; SectionsRead < MAX_SECTIONS-1; ){
        int marker = 0;
        int got;
        unsigned int ll,lh;
        unsigned int itemlen;
        uchar * Data;

        for (a=0;a<7;a++){
            marker = infile.getch();
            if (marker != 0xff) break;

            if (a >= 6){

                kdDebug(7034) << "too many padding bytes\n";
                return false;

            }
        }

        if (marker == 0xff){
            // 0xff is legal padding, but if we get that many, something's wrong.
            throw FatalError("too many padding bytes!");
        }

        Sections[SectionsRead].Type = marker;

        // Read the length of the section.
        lh = (uchar) infile.getch();
        ll = (uchar) infile.getch();

        itemlen = (lh << 8) | ll;

        if (itemlen < 2) {
            throw FatalError("invalid marker");
        }

        Sections[SectionsRead].Size = itemlen;

        Data = (uchar *)malloc(itemlen+1); // Add 1 to allow sticking a 0 at the end.
        Sections[SectionsRead].Data = Data;

        // Store first two pre-read bytes.
        Data[0] = (uchar)lh;
        Data[1] = (uchar)ll;

        got = infile.readBlock((char*)Data+2, itemlen-2); // Read the whole section.
        if (( unsigned ) got != itemlen-2){
            throw FatalError("reading from file");
        }
        SectionsRead++;

        switch(marker){

            case M_SOS:   // stop before hitting compressed data
                // If reading entire image is requested, read the rest of the data.
                if (ReadMode & READ_IMAGE){
                    unsigned long size;

                    size = kMax( 0ul, infile.size()-infile.at() );
                    Data = (uchar *)malloc(size);
                    if (Data == NULL){
                        throw FatalError("could not allocate data for entire image");
                    }

                    got = infile.readBlock((char*)Data,  size);
                    if (( unsigned ) got != size){
                        throw FatalError("could not read the rest of the image");
                    }

                    Sections[SectionsRead].Data = Data;
                    Sections[SectionsRead].Size = size;
                    Sections[SectionsRead].Type = PSEUDO_IMAGE_MARKER;
                    SectionsRead ++;
                    //HaveAll = 1;
                }
                return true;

            case M_EOI:   // in case it's a tables-only JPEG stream
                kdDebug(7034) << "No image in jpeg!\n";
                return false;

            case M_COM: // Comment section
		// pieczy 2002-02-12
		// now the User comment goes to UserComment
		// so we can store a Comment section also in READ_EXIF mode
		process_COM(Data, itemlen);
                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.
                free(Sections[--SectionsRead].Data);
                break;

            case M_EXIF:
                // Seen files from some 'U-lead' software with Vivitar scanner
                // that uses marker 31 for non exif stuff.  Thus make sure
                // it says 'Exif' in the section before treating it as exif.
                if ((ReadMode & READ_EXIF) && memcmp(Data+2, "Exif", 4) == 0){
                    process_EXIF((uchar *)Data, itemlen); // FIXME: This call
			// requires Data to be array of at least 8 bytes. Code
			// above only checks for itemlen < 2.
                }else{
                    // Discard this section.
                    free(Sections[--SectionsRead].Data);
                }
                break;

            case M_SOF0:
            case M_SOF1:
            case M_SOF2:
            case M_SOF3:
            case M_SOF5:
            case M_SOF6:
            case M_SOF7:
            case M_SOF9:
            case M_SOF10:
            case M_SOF11:
            case M_SOF13:
            case M_SOF14:
            case M_SOF15:
                process_SOFn(Data, marker); //FIXME: This call requires Data to
		// be array of at least 8 bytes. Code above only checks for 
		// itemlen < 2.
            default:
                break;
                break;
        }
    }
    return true;
}


//--------------------------------------------------------------------------
// Discard read data.
//--------------------------------------------------------------------------
void ExifData::DiscardData(void)
{
    for (int a=0; a < SectionsRead; a++)
        free(Sections[a].Data);
    SectionsRead = 0;
}

//--------------------------------------------------------------------------
// Convert a 16 bit unsigned value from file's native byte order
//--------------------------------------------------------------------------
int ExifData::Get16u(void * Short)
{
    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 ExifData::Get32s(void * Long)
{
    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 ExifData::Get32u(void * Long)
{
    return (unsigned)Get32s(Long) & 0xffffffff;
}

//--------------------------------------------------------------------------
// Evaluate number, be it int, rational, or float from directory.
//--------------------------------------------------------------------------
double ExifData::ConvertAnyFormat(void * ValuePtr, int Format)
{
    double Value;
    Value = 0;

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

        case FMT_USHORT:    Value = Get16u(ValuePtr);          break;

        case FMT_ULONG:     Value = Get32u(ValuePtr);          break;

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

        case FMT_SSHORT:    Value = (signed short)Get16u(ValuePtr);  break;
        case FMT_SLONG:     Value = Get32s(ValuePtr);                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;
    }
    return Value;
}

//--------------------------------------------------------------------------
// Process one of the nested EXIF directories.
//--------------------------------------------------------------------------
void ExifData::ProcessExifDir(unsigned char * DirStart, unsigned char * OffsetBase, unsigned ExifLength)
{
    int de;
    int a;
    int NumDirEntries;
    unsigned ThumbnailOffset = 0;
    unsigned ThumbnailSize = 0;

    NumDirEntries = Get16u(DirStart);
    #define DIR_ENTRY_ADDR(Start, Entry) (Start+2+12*(Entry))

    {
        unsigned char * DirEnd;
        DirEnd = DIR_ENTRY_ADDR(DirStart, NumDirEntries);
        if (DirEnd+4 > (OffsetBase+ExifLength)){
            if (DirEnd+2 == OffsetBase+ExifLength || DirEnd == OffsetBase+ExifLength){
                // Version 1.3 of jhead would truncate a bit too much.
                // This also caught later on as well.
            }else{
                // Note: Files that had thumbnails trimmed with jhead 1.3 or earlier
                // might trigger this.
                throw FatalError("Illegally sized directory");
            }
        }
        if (DirEnd < LastExifRefd) LastExifRefd = DirEnd;
    }

    for (de=0;de<NumDirEntries;de++){
        int Tag, Format, Components;
        unsigned char * ValuePtr;
        int ByteCount;
        char * DirEntry;
        DirEntry = (char *)DIR_ENTRY_ADDR(DirStart, de);

        Tag = Get16u(DirEntry);
        Format = Get16u(DirEntry+2);
        Components = Get32u(DirEntry+4);

        if ((Format-1) >= NUM_FORMATS) {
            // (-1) catches illegal zero case as unsigned underflows to positive large.
            throw FatalError("Illegal format code in EXIF dir");
        }

        ByteCount = Components * BytesPerFormat[Format];

        if (ByteCount > 4){
            unsigned OffsetVal;
            OffsetVal = Get32u(DirEntry+8);
            // If its bigger than 4 bytes, the dir entry contains an offset.
            if (OffsetVal+ByteCount > ExifLength){
                // Bogus pointer offset and / or bytecount value
                //printf("Offset %d bytes %d ExifLen %d\n",OffsetVal, ByteCount, ExifLength);

                throw FatalError("Illegal pointer offset value in EXIF");
            }
            ValuePtr = OffsetBase+OffsetVal;
        }else{
            // 4 bytes or less and value is in the dir entry itself
            ValuePtr = (unsigned char *)DirEntry+8;
        }

        if (LastExifRefd < ValuePtr+ByteCount){
            // Keep track of last byte in the exif header that was actually referenced.
            // That way, we know where the discardable thumbnail data begins.
            LastExifRefd = ValuePtr+ByteCount;
        }

        // Extract useful components of tag
        switch(Tag){

            case TAG_MAKE:
                ExifData::CameraMake = QString((char*)ValuePtr);
                break;

            case TAG_MODEL:
                ExifData::CameraModel = QString((char*)ValuePtr);
		break;

            case TAG_ORIENTATION:
                Orientation = (int)ConvertAnyFormat(ValuePtr, Format);
                break;

            case TAG_DATETIME_ORIGINAL:
		DateTime = QString((char*)ValuePtr);
                break;

            case TAG_USERCOMMENT:
                // Olympus has this padded with trailing spaces.  Remove these first.
                for (a=ByteCount;;){
                    a--;
                    if ((ValuePtr)[a] == ' '){
                        (ValuePtr)[a] = '\0';
                    }else{
                        break;
                    }
                    if (a == 0) break;
                }

                // Copy the comment
                if (memcmp(ValuePtr, "ASCII",5) == 0){
                    for (a=5;a<10;a++){
                        int c;
                        c = (ValuePtr)[a];
                        if (c != '\0' && c != ' '){
                            //strncpy(ImageInfo.Comments, (const char*)(a+ValuePtr), 199);
                            UserComment.sprintf("%s", (const char*)(a+ValuePtr));
                            break;
                        }
                    }
                }else{
                    //strncpy(ImageInfo.Comments, (const char*)ValuePtr, 199);
                    UserComment.sprintf("%s", (const char*)ValuePtr);
                }
                break;

            case TAG_FNUMBER:
                // Simplest way of expressing aperture, so I trust it the most.
                // (overwrite previously computd value if there is one)
		ExifData::ApertureFNumber = (float)ConvertAnyFormat(ValuePtr, Format);
                break;

            case TAG_APERTURE:
            case TAG_MAXAPERTURE:
                // More relevant info always comes earlier, so only use this field if we don't
                // have appropriate aperture information yet.
                if (ExifData::ApertureFNumber == 0){
                    ExifData::ApertureFNumber
                        = (float)exp(ConvertAnyFormat(ValuePtr, Format)*log(2.0)*0.5);
                }
                break;

            case TAG_FOCALLENGTH:
                // Nice digital cameras actually save the focal length as a function
                // of how far they are zoomed in.
                ExifData::FocalLength = (float)ConvertAnyFormat(ValuePtr, Format);
                break;

            case TAG_SUBJECT_DISTANCE:
                // Inidcates the distacne the autofocus camera is focused to.
                // Tends to be less accurate as distance increases.
                ExifData::Distance = (float)ConvertAnyFormat(ValuePtr, Format);
                break;

            case TAG_EXPOSURETIME:
                // Simplest way of expressing exposure time, so I trust it most.
                // (overwrite previously computd value if there is one)
                ExifData::ExposureTime = (float)ConvertAnyFormat(ValuePtr, Format);
                break;

            case TAG_SHUTTERSPEED:
                // More complicated way of expressing exposure time, so only use
                // this value if we don't already have it from somewhere else.
                if (ExifData::ExposureTime == 0){
                    ExifData::ExposureTime
                        = (float)(1/exp(ConvertAnyFormat(ValuePtr, Format)*log(2.0)));
                }
                break;

            case TAG_FLASH:
		ExifData::FlashUsed = (int)ConvertAnyFormat(ValuePtr, Format);
                break;

            case TAG_EXIF_IMAGELENGTH:
                ExifImageLength = (int)ConvertAnyFormat(ValuePtr, Format);
                break;

            case TAG_EXIF_IMAGEWIDTH:
                ExifImageWidth = (int)ConvertAnyFormat(ValuePtr, Format);
                break;

            case TAG_FOCALPLANEXRES:
                FocalplaneXRes = ConvertAnyFormat(ValuePtr, Format);
                break;

            case TAG_FOCALPLANEUNITS:
                switch((int)ConvertAnyFormat(ValuePtr, Format)){
                    case 1: FocalplaneUnits = 25.4; break; // inch
                    case 2:
                        // According to the information I was using, 2 means meters.
                        // But looking at the Cannon powershot's files, inches is the only
                        // sensible value.
                        FocalplaneUnits = 25.4;
                        break;

                    case 3: FocalplaneUnits = 10;   break;  // centimeter
                    case 4: FocalplaneUnits = 1;    break;  // milimeter
                    case 5: FocalplaneUnits = .001; break;  // micrometer
                }
                break;

                // Remaining cases contributed by: Volker C. Schoech (schoech@gmx.de)

            case TAG_EXPOSURE_BIAS:
	    	ExifData::ExposureBias = (float)ConvertAnyFormat(ValuePtr, Format);
		break;

            case TAG_WHITEBALANCE:
                 ExifData::Whitebalance = (int)ConvertAnyFormat(ValuePtr, Format);
		 break;

            case TAG_METERING_MODE:
                ExifData::MeteringMode = (int)ConvertAnyFormat(ValuePtr, Format);
                break;

            case TAG_EXPOSURE_PROGRAM:
                ExifData::ExposureProgram = (int)ConvertAnyFormat(ValuePtr, Format);
                break;

            case TAG_ISO_EQUIVALENT:
                ExifData::ISOequivalent = (int)ConvertAnyFormat(ValuePtr, Format);
                if ( ExifData::ISOequivalent < 50 ) ExifData::ISOequivalent *= 200;
                break;

            case TAG_COMPRESSION_LEVEL:
                ExifData::CompressionLevel = (int)ConvertAnyFormat(ValuePtr, Format);
                break;

            case TAG_THUMBNAIL_OFFSET:
                ThumbnailOffset = (unsigned)ConvertAnyFormat(ValuePtr, Format);
                break;

            case TAG_THUMBNAIL_LENGTH:
                ThumbnailSize = (unsigned)ConvertAnyFormat(ValuePtr, Format);
                break;

        }

        if (Tag == TAG_EXIF_OFFSET || Tag == TAG_INTEROP_OFFSET){
            unsigned char * SubdirStart;
            SubdirStart = OffsetBase + Get32u(ValuePtr);
            if (SubdirStart < OffsetBase || SubdirStart > OffsetBase+ExifLength){
                throw FatalError("Illegal subdirectory link");
            }
            ProcessExifDir(SubdirStart, OffsetBase, ExifLength);
            continue;
        }
    }

    {
        // In addition to linking to subdirectories via exif tags,
        // there's also a potential link to another directory at the end of each
        // directory.  this has got to be the result of a comitee!
        unsigned char * SubdirStart;
        unsigned Offset;

        if (DIR_ENTRY_ADDR(DirStart, NumDirEntries) + 4 <= OffsetBase+ExifLength){
            Offset = Get32u(DIR_ENTRY_ADDR(DirStart, NumDirEntries));
	    // There is at least one jpeg from an HP camera having an Offset of almost MAXUINT.
	    // Adding OffsetBase to it produces an overflow, so compare with ExifLength here.
	    // See http://bugs.kde.org/show_bug.cgi?id=54542
	    if (Offset && Offset < ExifLength){
                SubdirStart = OffsetBase + Offset;
                if (SubdirStart > OffsetBase+ExifLength){
                    if (SubdirStart < OffsetBase+ExifLength+20){
                        // Jhead 1.3 or earlier would crop the whole directory!
                        // As Jhead produces this form of format incorrectness,
                        // I'll just let it pass silently
                        kdDebug(7034) << "Thumbnail removed with Jhead 1.3 or earlier\n";
                    }else{
                        throw FatalError("Illegal subdirectory link 2");
                    }
                }else{
                    if (SubdirStart <= OffsetBase+ExifLength){
                        ProcessExifDir(SubdirStart, OffsetBase, ExifLength);
                    }
                }
            }
        }else{
            // The exif header ends before the last next directory pointer.
        }
    }

    if (ThumbnailSize && ThumbnailOffset){
        if (ThumbnailSize + ThumbnailOffset <= ExifLength){
            // The thumbnail pointer appears to be valid.  Store it.
	    Thumbnail.loadFromData(OffsetBase + ThumbnailOffset, ThumbnailSize, "JPEG");
        }
    }
}

//--------------------------------------------------------------------------
// Process a COM marker.  We want to leave the bytes unchanged.  The
// progam that displays this text may decide to remove blanks, convert
// newlines, or otherwise modify the text.  In particular we want to be
// safe for passing utf-8 text.
//--------------------------------------------------------------------------
void ExifData::process_COM (const uchar * Data, int length)
{
    Comment = QString::fromUtf8((char *)Data+2, (length-2));
}


//--------------------------------------------------------------------------
// Process a SOFn marker.  This is useful for the image dimensions
//--------------------------------------------------------------------------
void ExifData::process_SOFn (const uchar * Data, int marker)
{
    int data_precision, num_components;

    data_precision = Data[2];
    ExifData::Height = Get16m(Data+3);
    ExifData::Width = Get16m(Data+5);
    num_components = Data[7];

    if (num_components == 3){
        ExifData::IsColor = 1;
    }else{
        ExifData::IsColor = 0;
    }

    ExifData::Process = marker;

}

//--------------------------------------------------------------------------
// Get 16 bits motorola order (always) for jpeg header stuff.
//--------------------------------------------------------------------------
int ExifData::Get16m(const void * Short)
{
    return (((uchar *)Short)[0] << 8) | ((uchar *)Short)[1];
}


//--------------------------------------------------------------------------
// Process a EXIF marker
// Describes all the drivel that most digital cameras include...
//--------------------------------------------------------------------------
void ExifData::process_EXIF(unsigned char * CharBuf, unsigned int length)
{
    ExifData::FlashUsed = 0; // If it s from a digicam, and it used flash, it says so.

    FocalplaneXRes = 0;
    FocalplaneUnits = 0;
    ExifImageWidth = 0;
    ExifImageLength = 0;

    {   // Check the EXIF header component
        static const uchar ExifHeader[] = "Exif\0\0";
        if (memcmp(CharBuf+2, ExifHeader,6)){
            throw FatalError("Incorrect Exif header");
        }
    }

    if (memcmp(CharBuf+8,"II",2) == 0){
        // printf("Exif section in Intel order\n");
        MotorolaOrder = 0;
    }else{
        if (memcmp(CharBuf+8,"MM",2) == 0){
            // printf("Exif section in Motorola order\n");
            MotorolaOrder = 1;
        }else{
            throw FatalError("Invalid Exif alignment marker.");
        }
    }

    // Check the next two values for correctness.
    if (Get16u(CharBuf+10) != 0x2a
      || Get32u(CharBuf+12) != 0x08){
        throw FatalError("Invalid Exif start (1)");
    }

    LastExifRefd = CharBuf;

    // First directory starts 16 bytes in.  Offsets start at 8 bytes in.
    ProcessExifDir(CharBuf+16, CharBuf+8, length-6);

    // This is how far the interesting (non thumbnail) part of the exif went.
    ExifSettingsLength = LastExifRefd - CharBuf;

    // Compute the CCD width, in milimeters.
    if (FocalplaneXRes != 0){
	kdDebug(7034) << "ExifImageWidth " << ExifImageWidth << " FocalplaneUnits " << FocalplaneUnits << " FocalplaneXRes " << FocalplaneXRes << endl;
        ExifData::CCDWidth = (float)(ExifImageWidth * FocalplaneUnits / FocalplaneXRes);
    }
}

//--------------------------------------------------------------------------
// Convert exif time to Unix time structure
//--------------------------------------------------------------------------
int ExifData::Exif2tm(struct tm * timeptr, char * ExifTime)
{
    int a;

    timeptr->tm_wday = -1;

    // Check for format: YYYY:MM:DD HH:MM:SS format.
    a = sscanf(ExifTime, "%d:%d:%d %d:%d:%d",
            &timeptr->tm_year, &timeptr->tm_mon, &timeptr->tm_mday,
            &timeptr->tm_hour, &timeptr->tm_min, &timeptr->tm_sec);

    if (a == 6){
        timeptr->tm_isdst = -1;
        timeptr->tm_mon -= 1;      // Adjust for unix zero-based months
        timeptr->tm_year -= 1900;  // Adjust for year starting at 1900
        return true; // worked.
    }

    return false; // Wasn't in Exif date format.
}

//--------------------------------------------------------------------------
// Contructor for initialising
//--------------------------------------------------------------------------
ExifData::ExifData()
{
    ExifData::Whitebalance = -1;
    ExifData::MeteringMode = -1;
    ExifData::FlashUsed = 0;
    Orientation = 0;
    Height = 0;
    Width = 0;
    IsColor = 0;
    Process = 0;
    FocalLength = 0;
    ExposureTime = 0;
    ApertureFNumber = 0;
    Distance = 0;
    CCDWidth = 0;
    ExposureBias = 0;
    ExposureProgram = 0;
    ISOequivalent = 0;
    CompressionLevel = 0;
}

//--------------------------------------------------------------------------
// process a EXIF jpeg file
//--------------------------------------------------------------------------
bool ExifData::scan(const QString & path)
{
    int ret;

    QFile f(path);
    if ( !f.open(IO_ReadOnly) )
        return false;

    try {
        // Scan the JPEG headers.
        ret = ReadJpegSections(f, READ_EXIF);
    }
    catch (FatalError& e) {
        e.debug_print();
        f.close();
        return false;
    }

    if (ret == false){
        kdDebug(7034) << "Not JPEG file!\n";
        DiscardData();
        f.close();
        return false;
    }
    f.close();
    DiscardData();

    //now make the strings clean,
    // for exmaple my Casio is a "QV-4000   "
    CameraMake = CameraMake.stripWhiteSpace();
    CameraModel = CameraModel.stripWhiteSpace();
    UserComment = UserComment.stripWhiteSpace();
    Comment = Comment.stripWhiteSpace();
    return true;
}

//--------------------------------------------------------------------------
// Does the embedded thumbnail match the jpeg image?
//--------------------------------------------------------------------------
#ifndef JPEG_TOL
#define JPEG_TOL 0.02
#endif
bool ExifData::isThumbnailSane() {
  if (Thumbnail.isNull()) return false;

  // check whether thumbnail dimensions match the image
  // not foolproof, but catches some altered images (jpegtran -rotate)
  if (ExifImageLength != 0 && ExifImageLength != Height) return false;
  if (ExifImageWidth != 0 && ExifImageWidth != Width) return false;
  if (Thumbnail.width() == 0 || Thumbnail.height() == 0) return false;
  if (Height == 0 || Width == 0) return false;
  double d = (double)Height/Width*Thumbnail.width()/Thumbnail.height();
  return (1-JPEG_TOL < d) && (d < 1+JPEG_TOL);
}


//--------------------------------------------------------------------------
// return a thumbnail that respects the orientation flag
// only if it seems sane
//--------------------------------------------------------------------------
QImage ExifData::getThumbnail() {
  if (!isThumbnailSane()) return NULL;
  if (!Orientation || Orientation == 1) return Thumbnail;

  // now fix orientation
  QWMatrix M;
  QWMatrix flip= QWMatrix(-1,0,0,1,0,0);
  switch (Orientation) {  // notice intentional fallthroughs
    case 2: M = flip; break;
    case 4: M = flip;
    case 3: M.rotate(180); break;
    case 5: M = flip;
    case 6: M.rotate(90); break;
    case 7: M = flip;
    case 8: M.rotate(270); break;
    default: break; // should never happen
  }
  return Thumbnail.xForm(M);
}
