ungif.c

这是一个开放源代码的与WINNT/WIN2K/WIN2003兼容的操作系统

                } 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(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 = (GifFilePrivateType *)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;
    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 = 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) {
                  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);
}

/******************************************************************************
 * 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 = (GifFilePrivateType *) 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;
    }

    ungif_free(GifFile);

    return GIF_OK;
}