ungif.c 36.5 KB
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/*
 * Gif extracting routines - derived from libungif
 *
 * Portions Copyright 2006 Mike McCormack
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * This library 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
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA
 */

/*
 * Original copyright notice:
 *
 * The GIFLIB distribution is Copyright (c) 1997  Eric S. Raymond
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 */


/******************************************************************************
 *   "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).
 *****************************************************************************/

#include <stdlib.h>
#include <string.h>

#include <stdarg.h>
#include "windef.h"
#include "winbase.h"
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#include "ungif.h"
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#include "wine/debug.h"

WINE_DEFAULT_DEBUG_CHANNEL(wincodecs);
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static void *ungif_alloc( size_t sz )
{
    return HeapAlloc( GetProcessHeap(), 0, sz );
}

static void *ungif_calloc( size_t num, size_t sz )
{
    return HeapAlloc( GetProcessHeap(), HEAP_ZERO_MEMORY, num*sz );
}

static void *ungif_realloc( void *ptr, size_t sz )
{
    return HeapReAlloc( GetProcessHeap(), 0, ptr, sz );
}

static void ungif_free( void *ptr )
{
    HeapFree( GetProcessHeap(), 0, ptr );
}

#define LZ_MAX_CODE         4095    /* Biggest code possible in 12 bits. */
#define LZ_BITS             12

#define NO_SUCH_CODE        4098    /* Impossible code, to signal empty. */

typedef struct GifFilePrivateType {
    GifWord BitsPerPixel,     /* Bits per pixel (Codes uses at least this + 1). */
      ClearCode,   /* The CLEAR LZ code. */
      EOFCode,     /* The EOF LZ code. */
      RunningCode, /* The next code algorithm can generate. */
      RunningBits, /* The number of bits required to represent RunningCode. */
      MaxCode1,    /* 1 bigger than max. possible code, in RunningBits bits. */
      LastCode,    /* The code before the current code. */
      CrntCode,    /* Current algorithm code. */
      StackPtr,    /* For character stack (see below). */
      CrntShiftState;    /* Number of bits in CrntShiftDWord. */
    unsigned long CrntShiftDWord;   /* For bytes decomposition into codes. */
    unsigned long PixelCount;   /* Number of pixels in image. */
    InputFunc Read;     /* function to read gif input (TVT) */
    GifByteType Buf[256];   /* Compressed input is buffered here. */
    GifByteType Stack[LZ_MAX_CODE]; /* Decoded pixels are stacked here. */
    GifByteType Suffix[LZ_MAX_CODE + 1];    /* So we can trace the codes. */
    GifPrefixType Prefix[LZ_MAX_CODE + 1];
} GifFilePrivateType;

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

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

static int DGifGetExtensionNext(GifFileType * GifFile, GifByteType ** GifExtension);
static int DGifGetCodeNext(GifFileType * GifFile, GifByteType ** GifCodeBlock);

/******************************************************************************
 * Miscellaneous utility functions
 *****************************************************************************/

/* return smallest bitfield size n will fit in */
static int
BitSize(int n) {

    register int i;

    for (i = 1; i <= 8; i++)
        if ((1 << i) >= n)
            break;
    return (i);
}

/******************************************************************************
 * Color map object functions
 *****************************************************************************/

/*
 * Allocate a color map of given size; initialize with contents of
 * ColorMap if that pointer is non-NULL.
 */
static ColorMapObject *
MakeMapObject(int ColorCount,
              const GifColorType * ColorMap) {

    ColorMapObject *Object;

    /*** FIXME: Our ColorCount has to be a power of two.  Is it necessary to
     * make the user know that or should we automatically round up instead? */
    if (ColorCount != (1 << BitSize(ColorCount))) {
        return NULL;
    }

    Object = ungif_alloc(sizeof(ColorMapObject));
    if (Object == NULL) {
        return NULL;
    }

    Object->Colors = ungif_calloc(ColorCount, sizeof(GifColorType));
    if (Object->Colors == NULL) {
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        ungif_free(Object);
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        return NULL;
    }

    Object->ColorCount = ColorCount;
    Object->BitsPerPixel = BitSize(ColorCount);

    if (ColorMap) {
        memcpy(Object->Colors, ColorMap, ColorCount * sizeof(GifColorType));
    }

    return (Object);
}

/*
 * Free a color map object
 */
static void
FreeMapObject(ColorMapObject * Object) {

    if (Object != NULL) {
        ungif_free(Object->Colors);
        ungif_free(Object);
        /*** FIXME:
         * When we are willing to break API we need to make this function
         * FreeMapObject(ColorMapObject **Object)
         * and do this assignment to NULL here:
         * *Object = NULL;
         */
    }
}

static int
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AddExtensionBlock(Extensions *New,
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                  int Len,
                  const unsigned char ExtData[]) {

    ExtensionBlock *ep;

    if (New->ExtensionBlocks == NULL)
        New->ExtensionBlocks = ungif_alloc(sizeof(ExtensionBlock));
    else
        New->ExtensionBlocks = ungif_realloc(New->ExtensionBlocks,
                                      sizeof(ExtensionBlock) *
                                      (New->ExtensionBlockCount + 1));

    if (New->ExtensionBlocks == NULL)
        return (GIF_ERROR);

    ep = &New->ExtensionBlocks[New->ExtensionBlockCount++];

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    ep->ByteCount=Len + 3;
    ep->Bytes = ungif_alloc(ep->ByteCount + 3);
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    if (ep->Bytes == NULL)
        return (GIF_ERROR);

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    /* Extension Header */
    ep->Bytes[0] = 0x21;
    ep->Bytes[1] = New->Function;
    ep->Bytes[2] = Len;

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    if (ExtData) {
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        memcpy(ep->Bytes + 3, ExtData, Len);
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        ep->Function = New->Function;
    }

    return (GIF_OK);
}

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static int
AppendExtensionBlock(Extensions *New,
                     int Len,
                     const unsigned char ExtData[])
{
    ExtensionBlock *ep;

    if (New->ExtensionBlocks == NULL)
        return (GIF_ERROR);

    ep = &New->ExtensionBlocks[New->ExtensionBlockCount - 1];

    ep->Bytes = ungif_realloc(ep->Bytes, ep->ByteCount + Len + 1);
    if (ep->Bytes == NULL)
        return (GIF_ERROR);

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    ep->Bytes[ep->ByteCount] = Len;

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    if (ExtData)
        memcpy(ep->Bytes + ep->ByteCount + 1, ExtData, Len);
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    ep->ByteCount += Len + 1;
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    return (GIF_OK);
}

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static void
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FreeExtension(Extensions *Extensions)
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{
    ExtensionBlock *ep;

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    if ((Extensions == NULL) || (Extensions->ExtensionBlocks == NULL)) {
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        return;
    }
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    for (ep = Extensions->ExtensionBlocks;
         ep < (Extensions->ExtensionBlocks + Extensions->ExtensionBlockCount); ep++)
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        ungif_free(ep->Bytes);
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    ungif_free(Extensions->ExtensionBlocks);
    Extensions->ExtensionBlocks = NULL;
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}

/******************************************************************************
 * Image block allocation functions
******************************************************************************/

static void
FreeSavedImages(GifFileType * GifFile) {

    SavedImage *sp;

    if ((GifFile == NULL) || (GifFile->SavedImages == NULL)) {
        return;
    }
    for (sp = GifFile->SavedImages;
         sp < GifFile->SavedImages + GifFile->ImageCount; sp++) {
        if (sp->ImageDesc.ColorMap) {
            FreeMapObject(sp->ImageDesc.ColorMap);
            sp->ImageDesc.ColorMap = NULL;
        }

        ungif_free(sp->RasterBits);

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        if (sp->Extensions.ExtensionBlocks)
            FreeExtension(&sp->Extensions);
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    }
    ungif_free(GifFile->SavedImages);
    GifFile->SavedImages=NULL;
}

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

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    int i, BitsPerPixel, SortFlag;
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    GifByteType Buf[3];

    /* 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) {
        return GIF_ERROR;
    }
    GifFile->SColorResolution = (((Buf[0] & 0x70) + 1) >> 4) + 1;
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    SortFlag = (Buf[0] & 0x08) != 0;
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    BitsPerPixel = (Buf[0] & 0x07) + 1;
    GifFile->SBackGroundColor = Buf[1];
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    GifFile->SAspectRatio = Buf[2];
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    if (Buf[0] & 0x80) {    /* Do we have global color map? */

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

        /* Get the global color map: */
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        GifFile->SColorMap->SortFlag = SortFlag;
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        for (i = 0; i < GifFile->SColorMap->ColorCount; i++) {
            if (READ(GifFile, Buf, 3) != 3) {
                FreeMapObject(GifFile->SColorMap);
                GifFile->SColorMap = NULL;
                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.
 *****************************************************************************/
static int
DGifGetRecordType(GifFileType * GifFile,
                  GifRecordType * Type) {

    GifByteType Buf;

    if (READ(GifFile, &Buf, 1) != 1) {
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        /* Wine-specific behavior: Native accepts broken GIF files that have no
         * terminator, so we match this by treating EOF as a terminator. */
        *Type = TERMINATE_RECORD_TYPE;
        return GIF_OK;
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    }

    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;
          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.
 *****************************************************************************/
static int
DGifGetImageDesc(GifFileType * GifFile) {

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

    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) {
        return GIF_ERROR;
    }
    BitsPerPixel = (Buf[0] & 0x07) + 1;
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    SortFlag = (Buf[0] & 0x20) != 0;
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    GifFile->Image.Interlace = (Buf[0] & 0x40);
    if (Buf[0] & 0x80) {    /* Does this image have local color map? */

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

        /* Get the image local color map: */
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        GifFile->Image.ColorMap->SortFlag = SortFlag;
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        for (i = 0; i < GifFile->Image.ColorMap->ColorCount; i++) {
            if (READ(GifFile, Buf, 3) != 3) {
                FreeMapObject(GifFile->Image.ColorMap);
                GifFile->Image.ColorMap = NULL;
                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 = ungif_realloc(GifFile->SavedImages,
                                      sizeof(SavedImage) *
                                      (GifFile->ImageCount + 1))) == NULL) {
            return GIF_ERROR;
        }
    } else {
        if ((GifFile->SavedImages = ungif_alloc(sizeof(SavedImage))) == NULL) {
            return GIF_ERROR;
        }
    }

    sp = &GifFile->SavedImages[GifFile->ImageCount];
    sp->ImageDesc = GifFile->Image;
    if (GifFile->Image.ColorMap != NULL) {
        sp->ImageDesc.ColorMap = MakeMapObject(
                                 GifFile->Image.ColorMap->ColorCount,
                                 GifFile->Image.ColorMap->Colors);
        if (sp->ImageDesc.ColorMap == NULL) {
            return GIF_ERROR;
        }
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        sp->ImageDesc.ColorMap->SortFlag = GifFile->Image.ColorMap->SortFlag;
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    }
    sp->RasterBits = NULL;
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    sp->Extensions.ExtensionBlockCount = 0;
    sp->Extensions.ExtensionBlocks = NULL;
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    GifFile->ImageCount++;

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

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

    return GIF_OK;
}

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

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

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

    if ((Private->PixelCount -= LineLen) > 0xffff0000UL) {
        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)
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                {
                    WARN("GIF is not properly terminated\n");
                    break;
                }
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            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.
 *****************************************************************************/
static int
DGifGetExtension(GifFileType * GifFile,
                 int *ExtCode,
                 GifByteType ** Extension) {

    GifByteType Buf;

    if (READ(GifFile, &Buf, 1) != 1) {
        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).
 *****************************************************************************/
static int
DGifGetExtensionNext(GifFileType * GifFile,
                     GifByteType ** Extension) {

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

    if (READ(GifFile, &Buf, 1) != 1) {
        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) {
            return GIF_ERROR;
        }
    } else
        *Extension = NULL;

    return GIF_OK;
}

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

    unsigned char c[2];

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

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

/******************************************************************************
 * 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).
 *****************************************************************************/
static int
DGifGetCodeNext(GifFileType * GifFile,
                GifByteType ** CodeBlock) {

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

    if (READ(GifFile, &Buf, 1) != 1) {
        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) {
            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;
    GifPrefixType *Prefix;
    GifFilePrivateType *Private = GifFile->Private;

    READ(GifFile, &CodeSize, 1);    /* Read Code size from file. */
    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;
    GifPrefixType *Prefix;
    GifFilePrivateType *Private = 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 continuing 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) {
                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 {
            /* It's a 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 {
                /* It's a code 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
                 * order (that's what stack is good for!) for 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 {
                        return GIF_ERROR;
                    }
                } else
                    CrntPrefix = CrntCode;

                /* Now (if image is O.K.) we should not get a 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 cannot
                 * 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) {
                    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(const GifPrefixType *Prefix,
                  int Code,
                  int ClearCode) {

    int i = 0;

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

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

    GifFilePrivateType *Private = GifFile->Private;

    GifByteType NextByte;
    static const unsigned short CodeMasks[] = {
        0x0000, 0x0001, 0x0003, 0x0007,
        0x000f, 0x001f, 0x003f, 0x007f,
        0x00ff, 0x01ff, 0x03ff, 0x07ff,
        0x0fff
    };
    /* The image can't contain more than LZ_BITS per code. */
    if (Private->RunningBits > LZ_BITS) {
        return GIF_ERROR;
    }

    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 we're using LZ_BITS bits already and we're at the max code, just
     * keep using the table as it is, don't increment Private->RunningCode.
     */
    if (Private->RunningCode < LZ_MAX_CODE + 2 &&
            ++Private->RunningCode > Private->MaxCode1 &&
            Private->RunningBits < LZ_BITS) {
        Private->MaxCode1 <<= 1;
        Private->RunningBits++;
    }
    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 successful.
 *****************************************************************************/
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) {
            return GIF_ERROR;
        }
        /* There shouldn't be any empty data blocks here as the LZW spec
         * says the LZW termination code should come first.  Therefore we
         * shouldn't be inside this routine at that point.
         */
        if (Buf[0] == 0) {
            return GIF_ERROR;
        }
        if (READ(GifFile, &Buf[1], Buf[0]) != Buf[0]) {
            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;
882
    Extensions temp_save;
883 884 885 886 887 888 889 890 891 892 893 894 895 896 897 898 899 900 901 902 903 904 905 906

    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 = ungif_alloc(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) {
907 908
                  sp->Extensions.ExtensionBlocks = temp_save.ExtensionBlocks;
                  sp->Extensions.ExtensionBlockCount = temp_save.ExtensionBlockCount;
909 910 911 912 913 914 915

                  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. */
916
                  sp->Extensions.Function = sp->Extensions.ExtensionBlocks[0].Function;
917 918 919 920
              }
              break;

          case EXTENSION_RECORD_TYPE:
921
          {
922
              int Function;
923 924
              Extensions *Extensions;

925 926 927 928
              if (DGifGetExtension(GifFile, &Function, &ExtData) == GIF_ERROR)
                  return (GIF_ERROR);

              if (GifFile->ImageCount || Function == GRAPHICS_EXT_FUNC_CODE)
929 930 931 932
                  Extensions = &temp_save;
              else
                  Extensions = &GifFile->Extensions;

933 934
              Extensions->Function = Function;

935 936 937 938 939 940 941 942 943 944 945
              if (ExtData)
              {
                  /* Create an extension block with our data */
                  if (AddExtensionBlock(Extensions, ExtData[0], &ExtData[1]) == GIF_ERROR)
                      return (GIF_ERROR);
              }
              else /* Empty extension block */
              {
                  if (AddExtensionBlock(Extensions, 0, NULL) == GIF_ERROR)
                      return (GIF_ERROR);
              }
946

947
              while (ExtData != NULL) {
948 949
                  int Len;
                  GifByteType *Data;
950

951
                  if (DGifGetExtensionNext(GifFile, &ExtData) == GIF_ERROR)
952 953
                      return (GIF_ERROR);

954 955 956 957 958 959 960 961 962 963 964 965
                  if (ExtData)
                  {
                      Len = ExtData[0];
                      Data = &ExtData[1];
                  }
                  else
                  {
                      Len = 0;
                      Data = NULL;
                  }

                  if (AppendExtensionBlock(Extensions, Len, Data) == GIF_ERROR)
966 967 968
                      return (GIF_ERROR);
              }
              break;
969
          }
970 971 972 973 974 975 976 977 978 979 980 981 982 983 984 985 986 987 988 989 990 991 992 993 994 995 996 997 998 999 1000 1001 1002 1003 1004 1005 1006 1007 1008 1009 1010 1011 1012 1013 1014 1015 1016 1017 1018 1019 1020 1021 1022 1023 1024 1025 1026 1027 1028 1029 1030 1031 1032 1033 1034 1035 1036 1037 1038 1039 1040 1041 1042 1043 1044 1045 1046 1047 1048 1049 1050 1051 1052 1053 1054 1055 1056 1057 1058 1059 1060 1061 1062 1063 1064 1065 1066 1067 1068 1069 1070 1071 1072 1073

          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);
}

/******************************************************************************
 * 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;

    GifFile = ungif_alloc(sizeof(GifFileType));
    if (GifFile == NULL) {
        return NULL;
    }

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

    Private = ungif_alloc(sizeof(GifFilePrivateType));
    if (!Private) {
        ungif_free(GifFile);
        return NULL;
    }

    GifFile->Private = (void*)Private;

    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) {
        ungif_free(Private);
        ungif_free(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 (memcmp(GIF_STAMP, Buf, GIF_VERSION_POS) != 0) {
        ungif_free(Private);
        ungif_free(GifFile);
        return NULL;
    }

    if (DGifGetScreenDesc(GifFile) == GIF_ERROR) {
        ungif_free(Private);
        ungif_free(GifFile);
        return NULL;
    }

    return GifFile;
}

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

    GifFilePrivateType *Private;

    if (GifFile == NULL)
        return GIF_ERROR;

    Private = GifFile->Private;

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

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

    ungif_free(Private);
    Private = NULL;

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

1074 1075
    FreeExtension(&GifFile->Extensions);

1076 1077 1078 1079
    ungif_free(GifFile);

    return GIF_OK;
}