libsplashscreen/giflib/dgif_lib.c

/*
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code 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
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

/******************************************************************************
 *   "Gif-Lib" - Yet another gif library.
 *
 * Written by:  Gershon Elber            IBM PC Ver 1.1,    Aug. 1990
 ******************************************************************************
 * The kernel of the GIF Decoding process can be found here.
 ******************************************************************************
 * History:
 * 16 Jun 89 - Version 1.0 by Gershon Elber.
 *  3 Sep 90 - Version 1.1 by Gershon Elber (Support for Gif89, Unique names).
 *****************************************************************************/

/* !!!! */

#ifdef HAVE_CONFIG_H
#include <config.h>
#endif

#include <stdlib.h>
#if defined (__MSDOS__) && !defined(__DJGPP__) && !defined(__GNUC__)
#include <io.h>
#include <alloc.h>
#include <sys\stat.h>
#else
#include <sys/types.h>
#include <sys/stat.h>
#endif /* __MSDOS__ */

#ifdef _WIN32
#include <io.h>
#define _OPEN_BINARY
#else
#include <unistd.h>
#endif

#include <fcntl.h>

#include <stdio.h>
#include <string.h>
#include "gif_lib.h"
#include "gif_lib_private.h"

#define COMMENT_EXT_FUNC_CODE 0xfe  /* Extension function code for
                                       comment. */

/* avoid extra function call in case we use fread (TVT) */
#define READ(_gif,_buf,_len)                                     \
  (((GifFilePrivateType*)_gif->Private)->Read ?                   \
    (size_t)((GifFilePrivateType*)_gif->Private)->Read(_gif,_buf,_len) : \
    fread(_buf,1,_len,((GifFilePrivateType*)_gif->Private)->File))

static int DGifGetWord(GifFileType *GifFile, int *Word);
static int DGifSetupDecompress(GifFileType *GifFile);
static int DGifDecompressLine(GifFileType *GifFile, GifPixelType *Line,
                              int LineLen);
static int DGifGetPrefixChar(unsigned int *Prefix, int Code, int ClearCode);
static int DGifDecompressInput(GifFileType *GifFile, int *Code);
static int DGifBufferedInput(GifFileType *GifFile, GifByteType *Buf,
                             GifByteType *NextByte);

/******************************************************************************
 * Open a new gif file for read, given by its name.
 * Returns GifFileType pointer dynamically allocated which serves as the gif
 * info record. _GifError is cleared if succesfull.
 *****************************************************************************/
GifFileType *
DGifOpenFileName(const char *FileName) {
    int FileHandle;
    GifFileType *GifFile;

    if ((FileHandle = open(FileName, O_RDONLY
#if defined(__MSDOS__) || defined(_OPEN_BINARY)
                           | O_BINARY
#endif /* __MSDOS__ || _OPEN_BINARY */
         )) == -1) {
        _GifError = D_GIF_ERR_OPEN_FAILED;
        return NULL;
    }

    GifFile = DGifOpenFileHandle(FileHandle);
    if (GifFile == (GifFileType *)NULL)
        close(FileHandle);
    return GifFile;
}

/******************************************************************************
 * Update a new gif file, given its file handle.
 * Returns GifFileType pointer dynamically allocated which serves as the gif
 * info record. _GifError is cleared if succesfull.
 *****************************************************************************/
GifFileType *
DGifOpenFileHandle(int FileHandle) {

    unsigned char Buf[GIF_STAMP_LEN + 1];
    GifFileType *GifFile;
    GifFilePrivateType *Private;
    FILE *f;

    GifFile = (GifFileType *)malloc(sizeof(GifFileType));
    if (GifFile == NULL) {
        _GifError = D_GIF_ERR_NOT_ENOUGH_MEM;
        return NULL;
    }

    memset(GifFile, '\0', sizeof(GifFileType));

    Private = (GifFilePrivateType *)malloc(sizeof(GifFilePrivateType));
    if (Private == NULL) {
        _GifError = D_GIF_ERR_NOT_ENOUGH_MEM;
        free((char *)GifFile);
        return NULL;
    }
#ifdef __MSDOS__
    setmode(FileHandle, O_BINARY);    /* Make sure it is in binary mode. */
#endif /* __MSDOS__ */

    f = fdopen(FileHandle, "rb");    /* Make it into a stream: */

#ifdef __MSDOS__
    setvbuf(f, NULL, _IOFBF, GIF_FILE_BUFFER_SIZE);    /* And inc. stream
                                                          buffer. */
#endif /* __MSDOS__ */

    GifFile->Private = (VoidPtr)Private;
    Private->FileHandle = FileHandle;
    Private->File = f;
    Private->FileState = FILE_STATE_READ;
    Private->Read = 0;    /* don't use alternate input method (TVT) */
    GifFile->UserData = 0;    /* TVT */

    /* Lets see if this is a GIF file: */
    if (READ(GifFile, Buf, GIF_STAMP_LEN) != GIF_STAMP_LEN) {
        _GifError = D_GIF_ERR_READ_FAILED;
        fclose(f);
        free((char *)Private);
        free((char *)GifFile);
        return NULL;
    }

    /* The GIF Version number is ignored at this time. Maybe we should do
     * something more useful with it.  */
    Buf[GIF_STAMP_LEN] = 0;
    if (strncmp(GIF_STAMP, (const char*)Buf, GIF_VERSION_POS) != 0) {
        _GifError = D_GIF_ERR_NOT_GIF_FILE;
        fclose(f);
        free((char *)Private);
        free((char *)GifFile);
        return NULL;
    }

    if (DGifGetScreenDesc(GifFile) == GIF_ERROR) {
        fclose(f);
        free((char *)Private);
        free((char *)GifFile);
        return NULL;
    }

    _GifError = 0;

    return GifFile;
}

/******************************************************************************
 * GifFileType constructor with user supplied input function (TVT)
 *****************************************************************************/
GifFileType *
DGifOpen(void *userData,
         InputFunc readFunc) {

    unsigned char Buf[GIF_STAMP_LEN + 1];
    GifFileType *GifFile;
    GifFilePrivateType *Private;

    if (!readFunc) {
        _GifError = D_GIF_ERR_READ_FAILED;
        return NULL;
    }

    GifFile = (GifFileType *)malloc(sizeof(GifFileType));
    if (GifFile == NULL) {
        _GifError = D_GIF_ERR_NOT_ENOUGH_MEM;
        return NULL;
    }

    memset(GifFile, '\0', sizeof(GifFileType));

    Private = (GifFilePrivateType *)malloc(sizeof(GifFilePrivateType));
    if (!Private) {
        _GifError = D_GIF_ERR_NOT_ENOUGH_MEM;
        free((char *)GifFile);
        return NULL;
    }

    GifFile->Private = (VoidPtr)Private;
    Private->FileHandle = 0;
    Private->File = 0;
    Private->FileState = FILE_STATE_READ;

    Private->Read = readFunc;    /* TVT */
    GifFile->UserData = userData;    /* TVT */

    /* Lets see if this is a GIF file: */
    if (READ(GifFile, Buf, GIF_STAMP_LEN) != GIF_STAMP_LEN) {
        _GifError = D_GIF_ERR_READ_FAILED;
        free((char *)Private);
        free((char *)GifFile);
        return NULL;
    }

    /* The GIF Version number is ignored at this time. Maybe we should do
     * something more useful with it. */
    Buf[GIF_STAMP_LEN] = 0;
    if (strncmp(GIF_STAMP, (const char*)Buf, GIF_VERSION_POS) != 0) {
        _GifError = D_GIF_ERR_NOT_GIF_FILE;
        free((char *)Private);
        free((char *)GifFile);
        return NULL;
    }

    if (DGifGetScreenDesc(GifFile) == GIF_ERROR) {
        free((char *)Private);
        free((char *)GifFile);
        return NULL;
    }

    _GifError = 0;

    return GifFile;
}

/******************************************************************************
 * This routine should be called before any other DGif calls. Note that
 * this routine is called automatically from DGif file open routines.
 *****************************************************************************/
int
DGifGetScreenDesc(GifFileType * GifFile) {

    int i, BitsPerPixel;
    GifByteType Buf[3];
    GifFilePrivateType *Private = (GifFilePrivateType *)GifFile->Private;

    if (!IS_READABLE(Private)) {
        /* This file was NOT open for reading: */
        _GifError = D_GIF_ERR_NOT_READABLE;
        return GIF_ERROR;
    }

    /* Put the screen descriptor into the file: */
    if (DGifGetWord(GifFile, &GifFile->SWidth) == GIF_ERROR ||
        DGifGetWord(GifFile, &GifFile->SHeight) == GIF_ERROR)
        return GIF_ERROR;

    if (READ(GifFile, Buf, 3) != 3) {
        _GifError = D_GIF_ERR_READ_FAILED;
        return GIF_ERROR;
    }
    GifFile->SColorResolution = (((Buf[0] & 0x70) + 1) >> 4) + 1;
    BitsPerPixel = (Buf[0] & 0x07) + 1;
    GifFile->SBackGroundColor = Buf[1];
    if (Buf[0] & 0x80) {    /* Do we have global color map? */

        GifFile->SColorMap = MakeMapObject(1 << BitsPerPixel, NULL);
        if (GifFile->SColorMap == NULL) {
            _GifError = D_GIF_ERR_NOT_ENOUGH_MEM;
            return GIF_ERROR;
        }

        /* Get the global color map: */
        for (i = 0; i < GifFile->SColorMap->ColorCount; i++) {
            if (READ(GifFile, Buf, 3) != 3) {
                FreeMapObject(GifFile->SColorMap);
                _GifError = D_GIF_ERR_READ_FAILED;
                return GIF_ERROR;
            }
            GifFile->SColorMap->Colors[i].Red = Buf[0];
            GifFile->SColorMap->Colors[i].Green = Buf[1];
            GifFile->SColorMap->Colors[i].Blue = Buf[2];
        }
    } else {
        GifFile->SColorMap = NULL;
    }

    return GIF_OK;
}

/******************************************************************************
 * This routine should be called before any attempt to read an image.
 *****************************************************************************/
int
DGifGetRecordType(GifFileType * GifFile,
                  GifRecordType * Type) {

    GifByteType Buf;
    GifFilePrivateType *Private = (GifFilePrivateType *)GifFile->Private;

    if (!IS_READABLE(Private)) {
        /* This file was NOT open for reading: */
        _GifError = D_GIF_ERR_NOT_READABLE;
        return GIF_ERROR;
    }

    if (READ(GifFile, &Buf, 1) != 1) {
        _GifError = D_GIF_ERR_READ_FAILED;
        return GIF_ERROR;
    }

    switch (Buf) {
      case ',':
          *Type = IMAGE_DESC_RECORD_TYPE;
          break;
      case '!':
          *Type = EXTENSION_RECORD_TYPE;
          break;
      case ';':
          *Type = TERMINATE_RECORD_TYPE;
          break;
      default:
          *Type = UNDEFINED_RECORD_TYPE;
          _GifError = D_GIF_ERR_WRONG_RECORD;
          return GIF_ERROR;
    }

    return GIF_OK;
}

/******************************************************************************
 * This routine should be called before any attempt to read an image.
 * Note it is assumed the Image desc. header (',') has been read.
 *****************************************************************************/
int
DGifGetImageDesc(GifFileType * GifFile) {

    int i, BitsPerPixel;
    GifByteType Buf[3];
    GifFilePrivateType *Private = (GifFilePrivateType *)GifFile->Private;
    SavedImage *sp;

    if (!IS_READABLE(Private)) {
        /* This file was NOT open for reading: */
        _GifError = D_GIF_ERR_NOT_READABLE;
        return GIF_ERROR;
    }

    if (DGifGetWord(GifFile, &GifFile->Image.Left) == GIF_ERROR ||
        DGifGetWord(GifFile, &GifFile->Image.Top) == GIF_ERROR ||
        DGifGetWord(GifFile, &GifFile->Image.Width) == GIF_ERROR ||
        DGifGetWord(GifFile, &GifFile->Image.Height) == GIF_ERROR)
        return GIF_ERROR;
    if (READ(GifFile, Buf, 1) != 1) {
        _GifError = D_GIF_ERR_READ_FAILED;
        return GIF_ERROR;
    }
    BitsPerPixel = (Buf[0] & 0x07) + 1;
    GifFile->Image.Interlace = (Buf[0] & 0x40);
    if (Buf[0] & 0x80) {    /* Does this image have local color map? */

        /*** FIXME: Why do we check both of these in order to do this?
         * Why do we have both Image and SavedImages? */
        if (GifFile->Image.ColorMap && GifFile->SavedImages == NULL)
            FreeMapObject(GifFile->Image.ColorMap);

        GifFile->Image.ColorMap = MakeMapObject(1 << BitsPerPixel, NULL);
        if (GifFile->Image.ColorMap == NULL) {
            _GifError = D_GIF_ERR_NOT_ENOUGH_MEM;
            return GIF_ERROR;
        }

        /* Get the image local color map: */
        for (i = 0; i < GifFile->Image.ColorMap->ColorCount; i++) {
            if (READ(GifFile, Buf, 3) != 3) {
                FreeMapObject(GifFile->Image.ColorMap);
                _GifError = D_GIF_ERR_READ_FAILED;
                return GIF_ERROR;
            }
            GifFile->Image.ColorMap->Colors[i].Red = Buf[0];
            GifFile->Image.ColorMap->Colors[i].Green = Buf[1];
            GifFile->Image.ColorMap->Colors[i].Blue = Buf[2];
        }
    } else if (GifFile->Image.ColorMap) {
        FreeMapObject(GifFile->Image.ColorMap);
        GifFile->Image.ColorMap = NULL;
    }

    if (GifFile->SavedImages) {
        if ((GifFile->SavedImages = (SavedImage *)realloc(GifFile->SavedImages,
                                      sizeof(SavedImage) *
                                      (GifFile->ImageCount + 1))) == NULL) {
            _GifError = D_GIF_ERR_NOT_ENOUGH_MEM;
            return GIF_ERROR;
        }
    } else {
        if ((GifFile->SavedImages =
             (SavedImage *) malloc(sizeof(SavedImage))) == NULL) {
            _GifError = D_GIF_ERR_NOT_ENOUGH_MEM;
            return GIF_ERROR;
        }
    }

    sp = &GifFile->SavedImages[GifFile->ImageCount];
    memcpy(&sp->ImageDesc, &GifFile->Image, sizeof(GifImageDesc));
    if (GifFile->Image.ColorMap != NULL) {
        sp->ImageDesc.ColorMap = MakeMapObject(
                                 GifFile->Image.ColorMap->ColorCount,
                                 GifFile->Image.ColorMap->Colors);
        if (sp->ImageDesc.ColorMap == NULL) {
            _GifError = D_GIF_ERR_NOT_ENOUGH_MEM;
            return GIF_ERROR;
        }
    }
    sp->RasterBits = (unsigned char *)NULL;
    sp->ExtensionBlockCount = 0;
    sp->ExtensionBlocks = (ExtensionBlock *) NULL;

    GifFile->ImageCount++;

    Private->PixelCount = (long)GifFile->Image.Width *
       (long)GifFile->Image.Height;

    return DGifSetupDecompress(GifFile);  /* Reset decompress algorithm parameters. */
}

/******************************************************************************
 * Get one full scanned line (Line) of length LineLen from GIF file.
 *****************************************************************************/
int
DGifGetLine(GifFileType * GifFile,
            GifPixelType * Line,
            int LineLen) {

    GifByteType *Dummy;
    GifFilePrivateType *Private = (GifFilePrivateType *) GifFile->Private;

    if (!IS_READABLE(Private)) {
        /* This file was NOT open for reading: */
        _GifError = D_GIF_ERR_NOT_READABLE;
        return GIF_ERROR;
    }

    if (!LineLen)
        LineLen = GifFile->Image.Width;

#if defined(__MSDOS__) || defined(__GNUC__)
    if ((Private->PixelCount -= LineLen) > 0xffff0000UL) {
#else
    if ((Private->PixelCount -= LineLen) > 0xffff0000) {
#endif /* __MSDOS__ */
        _GifError = D_GIF_ERR_DATA_TOO_BIG;
        return GIF_ERROR;
    }

    if (DGifDecompressLine(GifFile, Line, LineLen) == GIF_OK) {
        if (Private->PixelCount == 0) {
            /* We probably would not be called any more, so lets clean
             * everything before we return: need to flush out all rest of
             * image until empty block (size 0) detected. We use GetCodeNext. */
            do
                if (DGifGetCodeNext(GifFile, &Dummy) == GIF_ERROR)
                    return GIF_ERROR;
            while (Dummy != NULL) ;
        }
        return GIF_OK;
    } else
        return GIF_ERROR;
}

/******************************************************************************
 * Put one pixel (Pixel) into GIF file.
 *****************************************************************************/
int
DGifGetPixel(GifFileType * GifFile,
             GifPixelType Pixel) {

    GifByteType *Dummy;
    GifFilePrivateType *Private = (GifFilePrivateType *) GifFile->Private;

    if (!IS_READABLE(Private)) {
        /* This file was NOT open for reading: */
        _GifError = D_GIF_ERR_NOT_READABLE;
        return GIF_ERROR;
    }
#if defined(__MSDOS__) || defined(__GNUC__)
    if (--Private->PixelCount > 0xffff0000UL)
#else
    if (--Private->PixelCount > 0xffff0000)
#endif /* __MSDOS__ */
    {
        _GifError = D_GIF_ERR_DATA_TOO_BIG;
        return GIF_ERROR;
    }

    if (DGifDecompressLine(GifFile, &Pixel, 1) == GIF_OK) {
        if (Private->PixelCount == 0) {
            /* We probably would not be called any more, so lets clean
             * everything before we return: need to flush out all rest of
             * image until empty block (size 0) detected. We use GetCodeNext. */
            do
                if (DGifGetCodeNext(GifFile, &Dummy) == GIF_ERROR)
                    return GIF_ERROR;
            while (Dummy != NULL) ;
        }
        return GIF_OK;
    } else
        return GIF_ERROR;
}

/******************************************************************************
 * Get an extension block (see GIF manual) from gif file. This routine only
 * returns the first data block, and DGifGetExtensionNext should be called
 * after this one until NULL extension is returned.
 * The Extension should NOT be freed by the user (not dynamically allocated).
 * Note it is assumed the Extension desc. header ('!') has been read.
 *****************************************************************************/
int
DGifGetExtension(GifFileType * GifFile,
                 int *ExtCode,
                 GifByteType ** Extension) {

    GifByteType Buf;
    GifFilePrivateType *Private = (GifFilePrivateType *)GifFile->Private;

    if (!IS_READABLE(Private)) {
        /* This file was NOT open for reading: */
        _GifError = D_GIF_ERR_NOT_READABLE;
        return GIF_ERROR;
    }

    if (READ(GifFile, &Buf, 1) != 1) {
        _GifError = D_GIF_ERR_READ_FAILED;
        return GIF_ERROR;
    }
    *ExtCode = Buf;

    return DGifGetExtensionNext(GifFile, Extension);
}

/******************************************************************************
 * Get a following extension block (see GIF manual) from gif file. This
 * routine should be called until NULL Extension is returned.
 * The Extension should NOT be freed by the user (not dynamically allocated).
 *****************************************************************************/
int
DGifGetExtensionNext(GifFileType * GifFile,
                     GifByteType ** Extension) {

    GifByteType Buf;
    GifFilePrivateType *Private = (GifFilePrivateType *)GifFile->Private;

    if (READ(GifFile, &Buf, 1) != 1) {
        _GifError = D_GIF_ERR_READ_FAILED;
        return GIF_ERROR;
    }
    if (Buf > 0) {
        *Extension = Private->Buf;    /* Use private unused buffer. */
        (*Extension)[0] = Buf;  /* Pascal strings notation (pos. 0 is len.). */
        if (READ(GifFile, &((*Extension)[1]), Buf) != Buf) {
            _GifError = D_GIF_ERR_READ_FAILED;
            return GIF_ERROR;
        }
    } else
        *Extension = NULL;

    return GIF_OK;
}

/******************************************************************************
 * This routine should be called last, to close the GIF file.
 *****************************************************************************/
int
DGifCloseFile(GifFileType * GifFile) {

    GifFilePrivateType *Private;
    FILE *File;

    if (GifFile == NULL)
        return GIF_ERROR;

    Private = (GifFilePrivateType *) GifFile->Private;

    if (!IS_READABLE(Private)) {
        /* This file was NOT open for reading: */
        _GifError = D_GIF_ERR_NOT_READABLE;
        return GIF_ERROR;
    }

    File = Private->File;

    if (GifFile->Image.ColorMap) {
        FreeMapObject(GifFile->Image.ColorMap);
        GifFile->Image.ColorMap = NULL;
    }

    if (GifFile->SColorMap) {
        FreeMapObject(GifFile->SColorMap);
        GifFile->SColorMap = NULL;
    }

    if (Private) {
        free((char *)Private);
        Private = NULL;
    }

    if (GifFile->SavedImages) {
        FreeSavedImages(GifFile);
        GifFile->SavedImages = NULL;
    }

    free(GifFile);

    if (File && (fclose(File) != 0)) {
        _GifError = D_GIF_ERR_CLOSE_FAILED;
        return GIF_ERROR;
    }
    return GIF_OK;
}

/******************************************************************************
 * Get 2 bytes (word) from the given file:
 *****************************************************************************/
static int
DGifGetWord(GifFileType * GifFile,
            int *Word) {

    unsigned char c[2];

    if (READ(GifFile, c, 2) != 2) {
        _GifError = D_GIF_ERR_READ_FAILED;
        return GIF_ERROR;
    }

    *Word = (((unsigned int)c[1]) << 8) + c[0];
    return GIF_OK;
}

/******************************************************************************
 * Get the image code in compressed form.  This routine can be called if the
 * information needed to be piped out as is. Obviously this is much faster
 * than decoding and encoding again. This routine should be followed by calls
 * to DGifGetCodeNext, until NULL block is returned.
 * The block should NOT be freed by the user (not dynamically allocated).
 *****************************************************************************/
int
DGifGetCode(GifFileType * GifFile,
            int *CodeSize,
            GifByteType ** CodeBlock) {

    GifFilePrivateType *Private = (GifFilePrivateType *)GifFile->Private;

    if (!IS_READABLE(Private)) {
        /* This file was NOT open for reading: */
        _GifError = D_GIF_ERR_NOT_READABLE;
        return GIF_ERROR;
    }

    *CodeSize = Private->BitsPerPixel;

    return DGifGetCodeNext(GifFile, CodeBlock);
}

/******************************************************************************
 * Continue to get the image code in compressed form. This routine should be
 * called until NULL block is returned.
 * The block should NOT be freed by the user (not dynamically allocated).
 *****************************************************************************/
int
DGifGetCodeNext(GifFileType * GifFile,
                GifByteType ** CodeBlock) {

    GifByteType Buf;
    GifFilePrivateType *Private = (GifFilePrivateType *)GifFile->Private;

    if (READ(GifFile, &Buf, 1) != 1) {
        _GifError = D_GIF_ERR_READ_FAILED;
        return GIF_ERROR;
    }

    if (Buf > 0) {
        *CodeBlock = Private->Buf;    /* Use private unused buffer. */
        (*CodeBlock)[0] = Buf;  /* Pascal strings notation (pos. 0 is len.). */
        if (READ(GifFile, &((*CodeBlock)[1]), Buf) != Buf) {
            _GifError = D_GIF_ERR_READ_FAILED;
            return GIF_ERROR;
        }
    } else {
        *CodeBlock = NULL;
        Private->Buf[0] = 0;    /* Make sure the buffer is empty! */
        Private->PixelCount = 0;    /* And local info. indicate image read. */
    }

    return GIF_OK;
}

/******************************************************************************
 * Setup the LZ decompression for this image:
 *****************************************************************************/
static int
DGifSetupDecompress(GifFileType * GifFile) {

    int i, BitsPerPixel;
    GifByteType CodeSize;
    unsigned int *Prefix;
    GifFilePrivateType *Private = (GifFilePrivateType *)GifFile->Private;

    READ(GifFile, &CodeSize, 1);    /* Read Code size from file. */
    if (CodeSize >= 12) {
        /* Invalid initial code size: report failure */
        return GIF_ERROR;
    }
    BitsPerPixel = CodeSize;

    Private->Buf[0] = 0;    /* Input Buffer empty. */
    Private->BitsPerPixel = BitsPerPixel;
    Private->ClearCode = (1 << BitsPerPixel);
    Private->EOFCode = Private->ClearCode + 1;
    Private->RunningCode = Private->EOFCode + 1;
    Private->RunningBits = BitsPerPixel + 1;    /* Number of bits per code. */
    Private->MaxCode1 = 1 << Private->RunningBits;    /* Max. code + 1. */
    Private->StackPtr = 0;    /* No pixels on the pixel stack. */
    Private->LastCode = NO_SUCH_CODE;
    Private->CrntShiftState = 0;    /* No information in CrntShiftDWord. */
    Private->CrntShiftDWord = 0;

    Prefix = Private->Prefix;
    for (i = 0; i <= LZ_MAX_CODE; i++)
        Prefix[i] = NO_SUCH_CODE;

    return GIF_OK;
}

/******************************************************************************
 * The LZ decompression routine:
 * This version decompress the given gif file into Line of length LineLen.
 * This routine can be called few times (one per scan line, for example), in
 * order the complete the whole image.
 *****************************************************************************/
static int
DGifDecompressLine(GifFileType * GifFile,
                   GifPixelType * Line,
                   int LineLen) {

    int i = 0;
    int j, CrntCode, EOFCode, ClearCode, CrntPrefix, LastCode, StackPtr;
    GifByteType *Stack, *Suffix;
    unsigned int *Prefix;
    GifFilePrivateType *Private = (GifFilePrivateType *) GifFile->Private;

    StackPtr = Private->StackPtr;
    Prefix = Private->Prefix;
    Suffix = Private->Suffix;
    Stack = Private->Stack;
    EOFCode = Private->EOFCode;
    ClearCode = Private->ClearCode;
    LastCode = Private->LastCode;

    if (StackPtr != 0) {
        /* Let pop the stack off before continueing to read the gif file: */
        while (StackPtr != 0 && i < LineLen)
            Line[i++] = Stack[--StackPtr];
    }

    while (i < LineLen) {    /* Decode LineLen items. */
        if (DGifDecompressInput(GifFile, &CrntCode) == GIF_ERROR)
            return GIF_ERROR;

        if (CrntCode == EOFCode) {
            /* Note however that usually we will not be here as we will stop
             * decoding as soon as we got all the pixel, or EOF code will
             * not be read at all, and DGifGetLine/Pixel clean everything.  */
            if (i != LineLen - 1 || Private->PixelCount != 0) {
                _GifError = D_GIF_ERR_EOF_TOO_SOON;
                return GIF_ERROR;
            }
            i++;
        } else if (CrntCode == ClearCode) {
            /* We need to start over again: */
            for (j = 0; j <= LZ_MAX_CODE; j++)
                Prefix[j] = NO_SUCH_CODE;
            Private->RunningCode = Private->EOFCode + 1;
            Private->RunningBits = Private->BitsPerPixel + 1;
            Private->MaxCode1 = 1 << Private->RunningBits;
            LastCode = Private->LastCode = NO_SUCH_CODE;
        } else {
            /* Its regular code - if in pixel range simply add it to output
             * stream, otherwise trace to codes linked list until the prefix
             * is in pixel range: */
            if (CrntCode < ClearCode) {
                /* This is simple - its pixel scalar, so add it to output: */
                Line[i++] = CrntCode;
            } else {
                /* Its a code to needed to be traced: trace the linked list
                 * until the prefix is a pixel, while pushing the suffix
                 * pixels on our stack. If we done, pop the stack in reverse
                 * (thats what stack is good for!) order to output.  */
                if (Prefix[CrntCode] == NO_SUCH_CODE) {
                    /* Only allowed if CrntCode is exactly the running code:
                     * In that case CrntCode = XXXCode, CrntCode or the
                     * prefix code is last code and the suffix char is
                     * exactly the prefix of last code! */
                    if (CrntCode == Private->RunningCode - 2) {
                        CrntPrefix = LastCode;
                        Suffix[Private->RunningCode - 2] =
                           Stack[StackPtr++] = DGifGetPrefixChar(Prefix,
                                                                 LastCode,
                                                                 ClearCode);
                    } else {
                        _GifError = D_GIF_ERR_IMAGE_DEFECT;
                        return GIF_ERROR;
                    }
                } else
                    CrntPrefix = CrntCode;

                /* Now (if image is O.K.) we should not get an NO_SUCH_CODE
                 * During the trace. As we might loop forever, in case of
                 * defective image, we count the number of loops we trace
                 * and stop if we got LZ_MAX_CODE. obviously we can not
                 * loop more than that.  */
                j = 0;
                while (j++ <= LZ_MAX_CODE &&
                       CrntPrefix > ClearCode && CrntPrefix <= LZ_MAX_CODE) {
                    Stack[StackPtr++] = Suffix[CrntPrefix];
                    CrntPrefix = Prefix[CrntPrefix];
                }
                if (j >= LZ_MAX_CODE || CrntPrefix > LZ_MAX_CODE) {
                    _GifError = D_GIF_ERR_IMAGE_DEFECT;
                    return GIF_ERROR;
                }
                /* Push the last character on stack: */
                Stack[StackPtr++] = CrntPrefix;

                /* Now lets pop all the stack into output: */
                while (StackPtr != 0 && i < LineLen)
                    Line[i++] = Stack[--StackPtr];
            }
            if (LastCode != NO_SUCH_CODE) {
                Prefix[Private->RunningCode - 2] = LastCode;

                if (CrntCode == Private->RunningCode - 2) {
                    /* Only allowed if CrntCode is exactly the running code:
                     * In that case CrntCode = XXXCode, CrntCode or the
                     * prefix code is last code and the suffix char is
                     * exactly the prefix of last code! */
                    Suffix[Private->RunningCode - 2] =
                       DGifGetPrefixChar(Prefix, LastCode, ClearCode);
                } else {
                    Suffix[Private->RunningCode - 2] =
                       DGifGetPrefixChar(Prefix, CrntCode, ClearCode);
                }
            }
            LastCode = CrntCode;
        }
    }

    Private->LastCode = LastCode;
    Private->StackPtr = StackPtr;

    return GIF_OK;
}

/******************************************************************************
 * Routine to trace the Prefixes linked list until we get a prefix which is
 * not code, but a pixel value (less than ClearCode). Returns that pixel value.
 * If image is defective, we might loop here forever, so we limit the loops to
 * the maximum possible if image O.k. - LZ_MAX_CODE times.
 *****************************************************************************/
static int
DGifGetPrefixChar(unsigned int *Prefix,
                  int Code,
                  int ClearCode) {

    int i = 0;

    while (Code > ClearCode && i++ <= LZ_MAX_CODE)
        Code = Prefix[Code];
    return Code;
}

/******************************************************************************
 * Interface for accessing the LZ codes directly. Set Code to the real code
 * (12bits), or to -1 if EOF code is returned.
 *****************************************************************************/
int
DGifGetLZCodes(GifFileType * GifFile,
               int *Code) {

    GifByteType *CodeBlock;
    GifFilePrivateType *Private = (GifFilePrivateType *)GifFile->Private;

    if (!IS_READABLE(Private)) {
        /* This file was NOT open for reading: */
        _GifError = D_GIF_ERR_NOT_READABLE;
        return GIF_ERROR;
    }

    if (DGifDecompressInput(GifFile, Code) == GIF_ERROR)
        return GIF_ERROR;

    if (*Code == Private->EOFCode) {
        /* Skip rest of codes (hopefully only NULL terminating block): */
        do {
            if (DGifGetCodeNext(GifFile, &CodeBlock) == GIF_ERROR)
                return GIF_ERROR;
        } while (CodeBlock != NULL) ;

        *Code = -1;
    } else if (*Code == Private->ClearCode) {
        /* We need to start over again: */
        Private->RunningCode = Private->EOFCode + 1;
        Private->RunningBits = Private->BitsPerPixel + 1;
        Private->MaxCode1 = 1 << Private->RunningBits;
    }

    return GIF_OK;
}

/******************************************************************************
 * The LZ decompression input routine:
 * This routine is responsable for the decompression of the bit stream from
 * 8 bits (bytes) packets, into the real codes.
 * Returns GIF_OK if read succesfully.
 *****************************************************************************/
static int
DGifDecompressInput(GifFileType * GifFile,
                    int *Code) {

    GifFilePrivateType *Private = (GifFilePrivateType *)GifFile->Private;

    GifByteType NextByte;
    static unsigned int CodeMasks[] = {
        0x0000, 0x0001, 0x0003, 0x0007,
        0x000f, 0x001f, 0x003f, 0x007f,
        0x00ff, 0x01ff, 0x03ff, 0x07ff,
        0x0fff
    };

    while (Private->CrntShiftState < Private->RunningBits) {
        /* Needs to get more bytes from input stream for next code: */
        if (DGifBufferedInput(GifFile, Private->Buf, &NextByte) == GIF_ERROR) {
            return GIF_ERROR;
        }
        Private->CrntShiftDWord |=
           ((unsigned long)NextByte) << Private->CrntShiftState;
        Private->CrntShiftState += 8;
    }
    *Code = Private->CrntShiftDWord & CodeMasks[Private->RunningBits];

    Private->CrntShiftDWord >>= Private->RunningBits;
    Private->CrntShiftState -= Private->RunningBits;

    /* If code cannot fit into RunningBits bits, must raise its size. Note
     * however that codes above 4095 are used for special signaling.  */
    if (++Private->RunningCode > Private->MaxCode1) {
        if (Private->RunningBits < LZ_BITS) {
            Private->MaxCode1 <<= 1;
            Private->RunningBits++;
        } else {
            Private->RunningCode = Private->MaxCode1;
        }
    }
    return GIF_OK;
}

/******************************************************************************
 * This routines read one gif data block at a time and buffers it internally
 * so that the decompression routine could access it.
 * The routine returns the next byte from its internal buffer (or read next
 * block in if buffer empty) and returns GIF_OK if succesful.
 *****************************************************************************/
static int
DGifBufferedInput(GifFileType * GifFile,
                  GifByteType * Buf,
                  GifByteType * NextByte) {

    if (Buf[0] == 0) {
        /* Needs to read the next buffer - this one is empty: */
        if (READ(GifFile, Buf, 1) != 1) {
            _GifError = D_GIF_ERR_READ_FAILED;
            return GIF_ERROR;
        }
        if (READ(GifFile, &Buf[1], Buf[0]) != Buf[0]) {
            _GifError = D_GIF_ERR_READ_FAILED;
            return GIF_ERROR;
        }
        *NextByte = Buf[1];
        Buf[1] = 2;    /* We use now the second place as last char read! */
        Buf[0]--;
    } else {
        *NextByte = Buf[Buf[1]++];
        Buf[0]--;
    }

    return GIF_OK;
}

/******************************************************************************
 * This routine reads an entire GIF into core, hanging all its state info off
 * the GifFileType pointer.  Call DGifOpenFileName() or DGifOpenFileHandle()
 * first to initialize I/O.  Its inverse is EGifSpew().
 ******************************************************************************/
int
DGifSlurp(GifFileType * GifFile) {

    int ImageSize;
    GifRecordType RecordType;
    SavedImage *sp;
    GifByteType *ExtData;
    SavedImage temp_save;

    temp_save.ExtensionBlocks = NULL;
    temp_save.ExtensionBlockCount = 0;

    do {
        if (DGifGetRecordType(GifFile, &RecordType) == GIF_ERROR)
            return (GIF_ERROR);

        switch (RecordType) {
          case IMAGE_DESC_RECORD_TYPE:
              if (DGifGetImageDesc(GifFile) == GIF_ERROR)
                  return (GIF_ERROR);

              sp = &GifFile->SavedImages[GifFile->ImageCount - 1];
              ImageSize = sp->ImageDesc.Width * sp->ImageDesc.Height;

              sp->RasterBits = (unsigned char *)malloc(ImageSize *
                                                       sizeof(GifPixelType));
              if (sp->RasterBits == NULL) {
                  return GIF_ERROR;
              }
              if (DGifGetLine(GifFile, sp->RasterBits, ImageSize) ==
                  GIF_ERROR)
                  return (GIF_ERROR);
              if (temp_save.ExtensionBlocks) {
                  sp->ExtensionBlocks = temp_save.ExtensionBlocks;
                  sp->ExtensionBlockCount = temp_save.ExtensionBlockCount;

                  temp_save.ExtensionBlocks = NULL;
                  temp_save.ExtensionBlockCount = 0;

                  /* FIXME: The following is wrong.  It is left in only for
                   * backwards compatibility.  Someday it should go away. Use
                   * the sp->ExtensionBlocks->Function variable instead. */
                  sp->Function = sp->ExtensionBlocks[0].Function;
              }
              break;

          case EXTENSION_RECORD_TYPE:
              if (DGifGetExtension(GifFile, &temp_save.Function, &ExtData) ==
                  GIF_ERROR)
                  return (GIF_ERROR);
              while (ExtData != NULL) {

                  /* Create an extension block with our data */
                  if (AddExtensionBlock(&temp_save, ExtData[0], &ExtData[1])
                      == GIF_ERROR)
                      return (GIF_ERROR);

                  if (DGifGetExtensionNext(GifFile, &ExtData) == GIF_ERROR)
                      return (GIF_ERROR);
                  temp_save.Function = 0;
              }
              break;

          case TERMINATE_RECORD_TYPE:
              break;

          default:    /* Should be trapped by DGifGetRecordType */
              break;
        }
    } while (RecordType != TERMINATE_RECORD_TYPE);

    /* Just in case the Gif has an extension block without an associated
     * image... (Should we save this into a savefile structure with no image
     * instead? Have to check if the present writing code can handle that as
     * well.... */
    if (temp_save.ExtensionBlocks)
        FreeExtension(&temp_save);

    return (GIF_OK);
}