exiv2/src/exif.cpp

// ***************************************************************** -*- C++ -*-
/*
 * Copyright (C) 2004 Andreas Huggel <ahuggel@gmx.net>
 * 
 * This program is part of the Exiv2 distribution.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 * 
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 * 
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
 */
/*
  File:      exif.cpp
  Version:   $Name:  $ $Revision: 1.20 $
  Author(s): Andreas Huggel (ahu) <ahuggel@gmx.net>
  History:   26-Jan-04, ahu: created
             11-Feb-04, ahu: isolated as a component
 */
// *****************************************************************************
#include "rcsid.hpp"
EXIV2_RCSID("@(#) $Name:  $ $Revision: 1.20 $ $RCSfile: exif.cpp,v $")

// *****************************************************************************
// included header files
#include "exif.hpp"
#include "types.hpp"
#include "error.hpp"
#include "value.hpp"
#include "ifd.hpp"
#include "tags.hpp"
#include "image.hpp"

// + standard includes
#include <iostream>
#include <iomanip>
#include <sstream>
#include <fstream>
#include <utility>
#include <algorithm>
#include <map>
#include <cstring>

// *****************************************************************************
// class member definitions
namespace Exif {

    Metadatum::Metadatum(const Entry& e, ByteOrder byteOrder)
        : tag_(e.tag()), ifdId_(e.ifdId()), ifdIdx_(e.ifdIdx()), value_(0)
    {
        value_ = Value::create(TypeId(e.type()));
        value_->read(e.data(), e.size(), byteOrder);
        key_ = ExifTags::makeKey(tag_, ifdId_);
    }

    Metadatum::Metadatum(const std::string& key, Value* value)
        : ifdIdx_(-1), value_(0), key_(key)
    {
        if (value) value_ = value->clone();
        std::pair<uint16, IfdId> p = ExifTags::decomposeKey(key);
        if (p.first == 0xffff) throw Error("Invalid key");
        tag_ = p.first;
        if (p.second == ifdIdNotSet) throw Error("Invalid key");
        ifdId_ = p.second;
    }

    Metadatum::~Metadatum()
    {
        delete value_;
    }

    Metadatum::Metadatum(const Metadatum& rhs)
        : tag_(rhs.tag_), ifdId_(rhs.ifdId_), 
          ifdIdx_(rhs.ifdIdx_), value_(0), key_(rhs.key_)
    {
        if (rhs.value_ != 0) value_ = rhs.value_->clone(); // deep copy
    }

    Metadatum& Metadatum::operator=(const Metadatum& rhs)
    {
        if (this == &rhs) return *this;
        tag_ = rhs.tag_;
        ifdId_ = rhs.ifdId_;
        ifdIdx_ = rhs.ifdIdx_;
        delete value_;
        value_ = 0;
        if (rhs.value_ != 0) value_ = rhs.value_->clone(); // deep copy
        key_ = rhs.key_;
        return *this;
    } // Metadatum::operator=
    
    void Metadatum::setValue(const Value* value)
    {
        delete value_;
        value_ = value->clone();
    }

    void Metadatum::setValue(const std::string& buf)
    {
        if (value_ == 0) value_ = Value::create(asciiString);
        value_->read(buf);
    }

    Thumbnail::Thumbnail()
        : type_(none), size_(0), image_(0), ifd_(ifd1, 0, false)
    {
    }

    Thumbnail::~Thumbnail()
    {
        delete[] image_;
    }

    Thumbnail::Thumbnail(const Thumbnail& rhs)
        : type_(rhs.type_), size_(rhs.size_), image_(0), ifd_(ifd1, 0, false)
    {
        if (rhs.image_ > 0 && rhs.size_ > 0) {
            image_ = new char[rhs.size_];
            memcpy(image_, rhs.image_, rhs.size_);
        }
        if (image_ && type_ == tiff) {
            tiffHeader_.read(image_);
            ifd_.read(image_ + tiffHeader_.offset(),
                      tiffHeader_.byteOrder(), tiffHeader_.offset());
        }
    }

    Thumbnail& Thumbnail::operator=(const Thumbnail& rhs)
    {
        type_ = rhs.type_;
        size_ = rhs.size_;
        delete[] image_;
        image_ = 0;
        if (rhs.image_ > 0 && rhs.size_ > 0) {
            image_ = new char[rhs.size_];
            memcpy(image_, rhs.image_, rhs.size_);
        }
        if (image_ && type_ == tiff) {
            tiffHeader_.read(image_);
            ifd_.read(image_ + tiffHeader_.offset(), 
                      tiffHeader_.byteOrder(), tiffHeader_.offset());
        }
        return *this;
    }

    int Thumbnail::read(const char* buf,
                        const ExifData& exifData,
                        ByteOrder byteOrder)
    {
        int rc = 0;
        std::string key = "Thumbnail.ImageStructure.Compression";
        ExifData::const_iterator pos = exifData.findKey(key);
        if (pos == exifData.end()) return -1; // no thumbnail
        long compression = pos->toLong();
        if (compression == 6) {
            rc = readJpegImage(buf, exifData);
        }
        else {
            rc = readTiffImage(buf, exifData, byteOrder);
        }
        return rc;
    } // Thumbnail::read

    int Thumbnail::readJpegImage(const char* buf, const ExifData& exifData) 
    {
        std::string key = "Thumbnail.RecordingOffset.JPEGInterchangeFormat";
        ExifData::const_iterator pos = exifData.findKey(key);
        if (pos == exifData.end()) return 1;
        long offset = pos->toLong();
        key = "Thumbnail.RecordingOffset.JPEGInterchangeFormatLength";
        pos = exifData.findKey(key);
        if (pos == exifData.end()) return 1;
        long size = pos->toLong();
        image_ = new char[size];
        memcpy(image_, buf + offset, size);
        size_ = size;
        type_ = jpeg;
        return 0;
    } // Thumbnail::readJpegImage

    int Thumbnail::readTiffImage(const char* buf,
                                 const ExifData& exifData,
                                 ByteOrder byteOrder)
    {
        char* data = new char[64*1024];     // temporary buffer Todo: handle larger
        memset(data, 0x0, 64*1024);         // images (which violate the Exif Std)
        long len = 0;                       // number of bytes in the buffer

        // Copy the TIFF header
        TiffHeader tiffHeader(byteOrder);
        len += tiffHeader.copy(data);

        // Create IFD (without Exif and GPS tags) from metadata
        Ifd ifd1(ifd1);
        addToIfd(ifd1, exifData.begin(), exifData.end(), tiffHeader.byteOrder());
        Ifd::iterator i = ifd1.findTag(0x8769);
        if (i != ifd1.end()) ifd1.erase(i);
        i = ifd1.findTag(0x8825);
        if (i != ifd1.end()) ifd1.erase(i);

        // Do not copy the IFD yet, remember the location and leave a gap
        long ifdOffset = len;
        len += ifd1.size() + ifd1.dataSize();

        // Copy thumbnail image data, remember the offsets used
        std::string key = "Thumbnail.RecordingOffset.StripOffsets";
        ExifData::const_iterator offsets = exifData.findKey(key);
        if (offsets == exifData.end()) return 2;
        key = "Thumbnail.RecordingOffset.StripByteCounts";
        ExifData::const_iterator sizes = exifData.findKey(key);
        if (sizes == exifData.end()) return 2;
        std::ostringstream os;                  // for the new strip offsets
        for (long k = 0; k < offsets->count(); ++k) {
            long offset = offsets->toLong(k);
            long size = sizes->toLong(k);
            memcpy(data + len, buf + offset, size);
            os << len << " ";
            len += size;
        }

        // Update the IFD with the actual strip offsets (replace existing entry)
        Metadatum newOffsets(*offsets);
        newOffsets.setValue(os.str());
        addToIfd(ifd1, newOffsets, tiffHeader.byteOrder());

        // Finally, sort and copy the IFD
        ifd1.sortByTag();
        ifd1.copy(data + ifdOffset, tiffHeader.byteOrder(), ifdOffset);

        image_ = new char[len];
        memcpy(image_, data, len);
        size_ = len;
        tiffHeader_.read(image_);
        ifd_.read(image_ + tiffHeader_.offset(), 
                  tiffHeader_.byteOrder(), tiffHeader_.offset());
        type_ = tiff;
        delete[] data;

        return 0;
    } // Thumbnail::readTiffImage

    int Thumbnail::write(const std::string& path) const
    {
        std::string p;
        switch (type_) {
        case jpeg: 
            p = path + ".jpg";
            break;
        case tiff:
            p = path + ".tif";
            break;
        case none:
            return 1;
            break;
        }
        std::ofstream file(p.c_str(), std::ios::binary);
        if (!file) return 1;
        file.write(image_, size_);
        if (!file.good()) return 2;
        return 0;
    } // Thumbnail::write

    void Thumbnail::update(ExifData& exifData) const
    {
        // Todo: properly synchronize the Exif data with the actual thumbnail,
        //       i.e., synch all relevant metadata

        switch (type_) {
        case jpeg: 
            updateJpegImage(exifData);
            break;
        case tiff:
            updateTiffImage(exifData);
            break;
        case none:
            /* do nothing */
            break;
        }

    } // Thumbnail::update

    void Thumbnail::updateJpegImage(ExifData& exifData) const
    {
        std::string key = "Thumbnail.RecordingOffset.JPEGInterchangeFormat";
        ExifData::iterator pos = exifData.findKey(key);
        if (pos == exifData.end()) {
            Value *value = Value::create(unsignedLong);
            exifData.add(key, value);
            delete value;
            pos = exifData.findKey(key);
        }
        pos->setValue("0");

        key = "Thumbnail.RecordingOffset.JPEGInterchangeFormatLength";
        pos = exifData.findKey(key);
        if (pos == exifData.end()) {
            Value *value = Value::create(unsignedLong);
            exifData.add(key, value);
            delete value;            
            pos = exifData.findKey(key);
        }
        pos->setValue(toString(size_));

    } // Thumbnail::updateJpegImage

    void Thumbnail::updateTiffImage(ExifData& exifData) const
    {
        // Create metadata from the StripOffsets and StripByteCounts entries
        // and add these to the Exif data, replacing existing entries
        Ifd::const_iterator pos = ifd_.findTag(0x0111);
        if (pos == ifd_.end()) throw Error("Bad thumbnail (0x0111)");
        exifData.add(Metadatum(*pos, tiffHeader_.byteOrder()));

        pos = ifd_.findTag(0x0117);
        if (pos == ifd_.end()) throw Error("Bad thumbnail (0x0117)");
        exifData.add(Metadatum(*pos, tiffHeader_.byteOrder()));

    } // Thumbnail::updateTiffImage

    long Thumbnail::copy(char* buf) const
    {
        long ret = 0;
        switch (type_) {
        case jpeg: 
            ret = copyJpegImage(buf);
            break;
        case tiff:
            ret = copyTiffImage(buf);
            break;
        case none:
            ret = 0;
            break;
        }
        return ret;
    }

    long Thumbnail::copyJpegImage(char* buf) const
    {
        memcpy(buf, image_, size_);
        return size_;
    }

    long Thumbnail::copyTiffImage(char* buf) const
    {
        long offset = ifd_.offset() + ifd_.size() + ifd_.dataSize();
        long size = size_ - offset;
        memcpy(buf, image_ + offset, size);
        return size;
    }

    long Thumbnail::size() const
    {
        long size = 0;
        switch (type_) {
        case jpeg: 
            size = size_;
            break;
        case tiff:
            size = size_ - ifd_.offset() - ifd_.size() - ifd_.dataSize();
            break;
        case none:
            size = 0;
            break;
        }
        return size;
    }

    void Thumbnail::setOffsets(Ifd& ifd1, ByteOrder byteOrder) const
    {
        switch (type_) {
        case jpeg: 
            setJpegImageOffsets(ifd1, byteOrder);
            break;
        case tiff:
            setTiffImageOffsets(ifd1, byteOrder);
            break;
        case none:
            /* do nothing */
            break;
        }        
    }

    void Thumbnail::setJpegImageOffsets(Ifd& ifd1, ByteOrder byteOrder) const
    {
        Ifd::iterator pos = ifd1.findTag(0x0201);
        if (pos == ifd1.end()) throw Error("Bad thumbnail (0x0201)");
        pos->setOffset(ifd1.offset() + ifd1.size() + ifd1.dataSize(), byteOrder);
    }

    void Thumbnail::setTiffImageOffsets(Ifd& ifd1, ByteOrder byteOrder) const
    {
        // Adjust the StripOffsets, assuming that the existing TIFF strips
        // start immediately after the thumbnail IFD
        long shift = ifd1.offset() + ifd1.size() + ifd1.dataSize() 
            - ifd_.offset() - ifd_.size() - ifd_.dataSize();
        Ifd::const_iterator pos = ifd_.findTag(0x0111);
        if (pos == ifd_.end()) throw Error("Bad thumbnail (0x0111)");
        Metadatum offsets(*pos, tiffHeader_.byteOrder());
        std::ostringstream os;
        for (long k = 0; k < offsets.count(); ++k) {
            os << offsets.toLong(k) + shift << " ";
        }
        offsets.setValue(os.str());

        // Write the offsets to IFD1, encoded in the corresponding byte order
        addToIfd(ifd1, offsets, byteOrder);

    } // Thumbnail::setTiffImageOffsets

    ExifData::ExifData() 
        : ifd0_(ifd0, 0, false), exifIfd_(exifIfd, 0, false), 
          iopIfd_(iopIfd, 0, false), gpsIfd_(gpsIfd, 0, false),
          ifd1_(ifd1, 0, false), valid_(false), size_(0), data_(0)
    {
    }

    ExifData::~ExifData()
    {
        delete[] data_;
    }

    int ExifData::read(const std::string& path)
    {
        JpegImage img;
        int rc = img.readExifData(path);
        if (rc) return rc;
        return read(img.exifData(), img.sizeExifData());
    }

    int ExifData::read(const char* buf, long len)
    {
        // Copy the data buffer
        delete[] data_;
        data_ = new char[len];
        memcpy(data_, buf, len);
        size_ = len;
        valid_ = true;

        // Read the TIFF header
        int ret = 0;
        int rc = tiffHeader_.read(data_);
        if (rc) return rc;

        // Read IFD0
        rc = ifd0_.read(data_ + tiffHeader_.offset(), 
                        byteOrder(), 
                        tiffHeader_.offset());
        if (rc) return rc;
        // Find and read ExifIFD sub-IFD of IFD0
        rc = ifd0_.readSubIfd(exifIfd_, data_, byteOrder(), 0x8769);
        if (rc) return rc;
        // Find and read Interoperability IFD in ExifIFD
        rc = exifIfd_.readSubIfd(iopIfd_, data_, byteOrder(), 0xa005);
        if (rc) return rc;
        // Find and read GPSInfo sub-IFD in IFD0
        rc = ifd0_.readSubIfd(gpsIfd_, data_, byteOrder(), 0x8825);
        if (rc) return rc;
        // Read IFD1
        if (ifd0_.next()) {
            rc = ifd1_.read(data_ + ifd0_.next(), byteOrder(), ifd0_.next());
            if (rc) return rc;
        }

        // Find and delete ExifIFD sub-IFD of IFD1
        Ifd::iterator pos = ifd1_.findTag(0x8769);
        if (pos != ifd1_.end()) {
            ifd1_.erase(pos);
            ret = -99;
        }
        // Find and delete GPSInfo sub-IFD in IFD1
        pos = ifd1_.findTag(0x8825);
        if (pos != ifd1_.end()) {
            ifd1_.erase(pos);
            ret = -99;
        }

        // Copy all entries from the IFDs to the internal metadata
        metadata_.clear();
        add(ifd0_.begin(), ifd0_.end(), byteOrder());
        add(exifIfd_.begin(), exifIfd_.end(), byteOrder());
        add(iopIfd_.begin(), iopIfd_.end(), byteOrder()); 
        add(gpsIfd_.begin(), gpsIfd_.end(), byteOrder());
        add(ifd1_.begin(), ifd1_.end(), byteOrder());

        // Read the thumbnail
        thumbnail_.read(data_, *this, byteOrder());

        return ret;
    } // ExifData::read

    int ExifData::write(const std::string& path) 
    {
        long size = this->size();
        char* buf = new char[size];
        long actualSize = copy(buf);
        if (actualSize > size) {
            throw Error("Invariant violated in ExifData::write");
        }
        JpegImage img;
        img.setExifData(buf, actualSize);
        return img.writeExifData(path);
    } // ExifData::write

    long ExifData::copy(char* buf)
    {
        long size = 0;
        // If we can update the internal IFDs and the underlying data buffer
        // from the metadata without changing the data size, then it is enough
        // to copy the data buffer.
        if (updateIfds()) {

//ahu Todo: remove debugging output
std::cout << "->>>>>> using non-intrusive writing <<<<<<-\n";

            memcpy(buf, data_, size_);
            size = size_;
        }
        // Else we have to do it the hard way...
        else {

//ahu Todo: remove debugging output
std::cout << "->>>>>> writing from metadata <<<<<<-\n";

            size = copyFromMetadata(buf);
        }
        return size;
    }

    long ExifData::copyFromMetadata(char* buf)
    {
        // Copy the TIFF header
        long ifd0Offset = tiffHeader_.copy(buf);

        // Build IFD0
        Ifd ifd0(ifd0, ifd0Offset);
        addToIfd(ifd0, begin(), end(), byteOrder());

        // Build Exif IFD from metadata
        long exifIfdOffset = ifd0Offset + ifd0.size() + ifd0.dataSize();
        Ifd exifIfd(exifIfd, exifIfdOffset);
        addToIfd(exifIfd, begin(), end(), byteOrder());

        // Set the offset to the Exif IFD in IFD0
        ifd0.erase(0x8769);
        if (exifIfd.size() > 0) {
            ifd0.setOffset(0x8769, exifIfdOffset, byteOrder());
        }

        // Build Interoperability IFD from metadata
        long iopIfdOffset = exifIfdOffset + exifIfd.size() + exifIfd.dataSize();
        Ifd iopIfd(iopIfd, iopIfdOffset);
        addToIfd(iopIfd, begin(), end(), byteOrder());

        // Set the offset to the Interoperability IFD in Exif IFD
        exifIfd.erase(0xa005);
        if (iopIfd.size() > 0) {
            exifIfd.setOffset(0xa005, iopIfdOffset, byteOrder());
        }

        // Build GPSInfo IFD from metadata
        long gpsIfdOffset = iopIfdOffset + iopIfd.size() + iopIfd.dataSize();
        Ifd gpsIfd(gpsIfd, gpsIfdOffset);
        addToIfd(gpsIfd, begin(), end(), byteOrder());

        // Set the offset to the GPSInfo IFD in IFD0
        ifd0.erase(0x8825);
        if (gpsIfd.size() > 0) {
            ifd0.setOffset(0x8825, gpsIfdOffset, byteOrder());
        }

        // Update Exif data from thumbnail, build IFD1 from updated metadata
        thumbnail_.update(*this);
        long ifd1Offset = gpsIfdOffset + gpsIfd.size() + gpsIfd.dataSize();
        Ifd ifd1(ifd1, ifd1Offset);
        addToIfd(ifd1, begin(), end(), byteOrder());
        thumbnail_.setOffsets(ifd1, byteOrder());
        long thumbOffset = ifd1Offset + ifd1.size() + ifd1.dataSize();

        // Set the offset to IFD1 in IFD0
        if (ifd1.size() > 0) {
            ifd0.setNext(ifd1Offset);
        }

        // Copy all IFDs and the thumbnail image to the data buffer
        ifd0.sortByTag();
        ifd0.copy(buf + ifd0Offset, byteOrder(), ifd0Offset);
        exifIfd.sortByTag();
        exifIfd.copy(buf + exifIfdOffset, byteOrder(), exifIfdOffset);
        iopIfd.sortByTag();
        iopIfd.copy(buf + iopIfdOffset, byteOrder(), iopIfdOffset);
        gpsIfd.sortByTag();
        gpsIfd.copy(buf + gpsIfdOffset, byteOrder(), gpsIfdOffset);
        ifd1.sortByTag();
        ifd1.copy(buf + ifd1Offset, byteOrder(), ifd1Offset);
        long len = thumbnail_.copy(buf + thumbOffset);

        return len + thumbOffset;

    } // ExifData::copyFromMetadata

    long ExifData::size() const
    {
        long size;
        if (compatible()) {
            size = size_;
        }
        else {
            size = tiffHeader_.size();
            std::map<IfdId, int> ifdEntries;
            const_iterator mdEnd = this->end();
            for (const_iterator md = begin(); md != mdEnd; ++md) {
                size += md->size();
                ifdEntries[md->ifdId()] += 1;
            }
            std::map<IfdId, int>::const_iterator eEnd = ifdEntries.end();
            std::map<IfdId, int>::const_iterator e;
            for (e = ifdEntries.begin(); e != eEnd; ++e) {
                size += 2 + 12 * e->second + 4;
            }
            size += thumbnail_.size();
            // Add 1k to account for the possibility that Thumbnail::update
            // may add entries to IFD1
            size += 1024;
        }
        return size;
    }

    void ExifData::add(Ifd::const_iterator begin, 
                       Ifd::const_iterator end,
                       ByteOrder byteOrder)
    {
        Ifd::const_iterator i = begin;
        for (; i != end; ++i) {
            add(Metadatum(*i, byteOrder));
        }
    }

    void ExifData::add(const std::string& key, Value* value)
    {
        add(Metadatum(key, value));
    }

    void ExifData::add(const Metadatum& metadatum)
    {
        iterator i = findKey(metadatum.key());
        if (i != end()) {
            i->setValue(&metadatum.value());
        }
        else {
            metadata_.push_back(metadatum);
        }
    }

    ExifData::const_iterator ExifData::findKey(const std::string& key) const
    {
        return std::find_if(metadata_.begin(), metadata_.end(),
                            FindMetadatumByKey(key));
    }

    ExifData::iterator ExifData::findKey(const std::string& key)
    {
        return std::find_if(metadata_.begin(), metadata_.end(),
                            FindMetadatumByKey(key));
    }

    void ExifData::sortByKey()
    {
        std::sort(metadata_.begin(), metadata_.end(), cmpMetadataByKey);
    }

    void ExifData::sortByTag()
    {
        std::sort(metadata_.begin(), metadata_.end(), cmpMetadataByTag);
    }

    void ExifData::erase(const std::string& key)
    {
        iterator pos = findKey(key);
        if (pos != end()) erase(pos);
    }

    void ExifData::erase(ExifData::iterator pos)
    {
        metadata_.erase(pos);
    }

    bool ExifData::updateIfds()
    {
        if (!this->compatible()) return false;

        bool compatible = true;
        compatible |= updateIfd(ifd0_);
        compatible |= updateIfd(exifIfd_);
        compatible |= updateIfd(iopIfd_);
        compatible |= updateIfd(gpsIfd_);
        compatible |= updateIfd(ifd1_);
        
        return compatible;
    } // ExifData::updateIfds

    bool ExifData::updateIfd(Ifd& ifd)
    {
        if (ifd.alloc()) throw Error("Invariant violated in ExifData::updateIfd");

        bool compatible = true;
        Ifd::iterator end = ifd.end();
        for (Ifd::iterator entry = ifd.begin(); entry != end; ++entry) {
            // find the corresponding metadatum
            std::string key = ExifTags::makeKey(entry->tag(), entry->ifdId());
            const_iterator md = findKey(key);
            if (md == this->end()) {
                // corresponding metadatum was deleted: this is not (yet) a
                // supported non-intrusive write operation.
                compatible = false;
                continue;
            }
            char* buf = new char[md->size()];
            md->copy(buf, byteOrder());
            entry->setValue(md->typeId(), buf, md->size());
            delete[] buf;
        }
        return compatible;
    } // ExifData::updateIfd

    bool ExifData::compatible() const
    {
        bool compatible = true;
        const_iterator end = this->end();
        for (const_iterator md = begin(); md != end; ++md) {
            // Check if the metadatum is compatible with the 
            // corresponding IFD entry
            const Ifd* ifd = getIfd(md->ifdId());
            if (!ifd) {
                compatible = false;
                break;
            }            
            Ifd::const_iterator entry = ifd->findTag(md->tag());
            if (entry == ifd->end()) {
                compatible = false;
                break;
            }
            if (md->size() > entry->size()) {
                compatible = false;
                break;
            }
        }
        return compatible;
    }

    const Ifd* ExifData::getIfd(IfdId ifdId) const
    {
        const Ifd* ifd = 0;
        switch (ifdId) {
        case ifd0: 
            ifd = &ifd0_;
            break;
        case exifIfd: 
            ifd = &exifIfd_;
            break;
        case iopIfd: 
            ifd = &iopIfd_;
            break;
        case gpsIfd: 
            ifd = &gpsIfd_;
            break;
        case ifd1: 
            ifd = &ifd1_;
            break;
        default:
            ifd = 0;
            break;
        }
        return ifd;
    }

    // *************************************************************************
    // free functions

    void addToIfd(Ifd& ifd, 
                  Metadata::const_iterator begin, 
                  Metadata::const_iterator end, 
                  ByteOrder byteOrder)
    {
        for (Metadata::const_iterator i = begin; i != end; ++i) {
            // add only metadata with matching IFD id
            if (i->ifdId() == ifd.ifdId()) {
                addToIfd(ifd, *i, byteOrder);
            }
        }
    } // addToIfd

    void addToIfd(Ifd& ifd, const Metadatum& metadatum, ByteOrder byteOrder)
    {
        // Todo: Implement Assert (Stroustup 24.3.7.2)
        if (!ifd.alloc()) throw Error("Invariant violated in addToIfd");

        RawEntry e;
        e.ifdId_ = metadatum.ifdId();
        e.ifdIdx_ = metadatum.ifdIdx();
        e.tag_ = metadatum.tag();
        e.type_ = metadatum.typeId();
        e.count_ = metadatum.count();
        e.size_ = metadatum.size();
        e.offset_ = 0;  // will be calculated when the IFD is written
        char* buf = 0;
        if (e.size_ > 4) {
            buf = new char[e.size_];
            metadatum.copy(buf, byteOrder);
        }
        else {
            metadatum.copy(e.offsetData_, byteOrder);
        }
        ifd.add(Entry(e, buf, ifd.alloc()));
        delete[] buf;
    } // addToIfd

    bool cmpMetadataByTag(const Metadatum& lhs, const Metadatum& rhs)
    {
        return lhs.tag() < rhs.tag();
    }

    bool cmpMetadataByKey(const Metadatum& lhs, const Metadatum& rhs)
    {
        return lhs.key() < rhs.key();
    }

    std::ostream& operator<<(std::ostream& os, const Metadatum& md)
    {
        PrintFct fct = ExifTags::printFct(md.tag(), md.ifdId());
        return fct(os, md.value());
    }

}                                       // namespace Exif