xtifffaxdecoder.java

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        bitPointer = 0;
        bytePointer = 0;

        int scanlineStride = (w + 7) / 8;

        int a0, a1, b1, b2;
        int[] b = new int[2];
        int entry, code, bits, color;
        boolean isWhite;
        int currIndex = 0;
        int temp[];

        // fillBits - dealt with this in readEOL
        // 1D/2D encoding - dealt with this in readEOL

        // uncompressedMode - haven't dealt with this yet.
        // TODO: Deal with uncompressedMode, aastha 03/03/1999

        oneD = (int) (tiffT4Options & 0x01);
        uncompressedMode = (int) ((tiffT4Options & 0x02) >> 1);
        fillBits = (int) ((tiffT4Options & 0x04) >> 2);

        // The data must start with an EOL code
        if (readEOL() != 1) {
            throw new Error(JaiI18N.getString("XTIFFFaxDecoder3"));
        }

        int lineOffset = 0;
        int bitOffset;

        // Then the 1D encoded scanline data will occur, changing elements
        // array gets set.
        decodeNextScanline(buffer, lineOffset, startX);
        lineOffset += scanlineStride;

        for (int lines = 1; lines < height; lines++) {

            // Every line must begin with an EOL followed by a bit which
            // indicates whether the following scanline is 1D or 2D encoded.
            if (readEOL() == 0) {
                // 2D encoded scanline follows

                // Initialize previous scanlines changing elements, and
                // initialize current scanline's changing elements array
                temp = prevChangingElems;
                prevChangingElems = currChangingElems;
                currChangingElems = temp;
                currIndex = 0;

                // a0 has to be set just before the start of this scanline.
                a0 = -1;
                isWhite = true;
                bitOffset = startX;

                lastChangingElement = 0;

                while (bitOffset < w) {
                    // Get the next changing element
                    getNextChangingElement(a0, isWhite, b);

                    b1 = b[0];
                    b2 = b[1];

                    // Get the next seven bits
                    entry = nextLesserThan8Bits(7);

                    // Run these through the 2DCodes table
                    entry = (int) (twoDCodes[entry] & 0xff);

                    // Get the code and the number of bits used up
                    code = (entry & 0x78) >>> 3;
                    bits = entry & 0x07;

                    if (code == 0) {
                        if (!isWhite) {
                            setToBlack(buffer, lineOffset, bitOffset, b2
                                    - bitOffset);
                        }
                        bitOffset = a0 = b2;

                        // Set pointer to consume the correct number of bits.
                        updatePointer(7 - bits);
                    } else if (code == 1) {
                        // Horizontal
                        updatePointer(7 - bits);

                        // identify the next 2 codes.
                        int number;
                        if (isWhite) {
                            number = decodeWhiteCodeWord();
                            bitOffset += number;
                            currChangingElems[currIndex++] = bitOffset;

                            number = decodeBlackCodeWord();
                            setToBlack(buffer, lineOffset, bitOffset, number);
                            bitOffset += number;
                            currChangingElems[currIndex++] = bitOffset;
                        } else {
                            number = decodeBlackCodeWord();
                            setToBlack(buffer, lineOffset, bitOffset, number);
                            bitOffset += number;
                            currChangingElems[currIndex++] = bitOffset;

                            number = decodeWhiteCodeWord();
                            bitOffset += number;
                            currChangingElems[currIndex++] = bitOffset;
                        }

                        a0 = bitOffset;
                    } else if (code <= 8) {
                        // Vertical
                        a1 = b1 + (code - 5);

                        currChangingElems[currIndex++] = a1;

                        // We write the current color till a1 - 1 pos,
                        // since a1 is where the next color starts
                        if (!isWhite) {
                            setToBlack(buffer, lineOffset, bitOffset, a1
                                    - bitOffset);
                        }
                        bitOffset = a0 = a1;
                        isWhite = !isWhite;

                        updatePointer(7 - bits);
                    } else {
                        throw new Error(JaiI18N.getString("XTIFFFaxDecoder4"));
                    }
                }

                // Add the changing element beyond the current scanline for the
                // other color too
                currChangingElems[currIndex++] = bitOffset;
                changingElemSize = currIndex;
            } else {
                // 1D encoded scanline follows
                decodeNextScanline(buffer, lineOffset, startX);
            }

            lineOffset += scanlineStride;
        }
    }

    public synchronized void decodeT6(byte[] buffer, byte[] compData,
                                      int startX, int height, long tiffT6Options) {
        this.data = compData;
        compression = 4;

        bitPointer = 0;
        bytePointer = 0;

        int scanlineStride = (w + 7) / 8;
        int bufferOffset = 0;

        int a0, a1, b1, b2;
        int entry, code, bits;
        byte color;
        boolean isWhite;
        int currIndex;
        int temp[];

        // Return values from getNextChangingElement
        int[] b = new int[2];

        // uncompressedMode - have written some code for this, but this
        // has not been tested due to lack of test images using this optional
        // extension. This code is when code == 11. aastha 03/03/1999
        uncompressedMode = (int) ((tiffT6Options & 0x02) >> 1);

        // Local cached reference
        int[] cce = currChangingElems;

        // Assume invisible preceding row of all white pixels and insert
        // both black and white changing elements beyond the end of this
        // imaginary scanline.
        changingElemSize = 0;
        cce[changingElemSize++] = w;
        cce[changingElemSize++] = w;

        int lineOffset = 0;
        int bitOffset;

        for (int lines = 0; lines < height; lines++) {
            // a0 has to be set just before the start of the scanline.
            a0 = -1;
            isWhite = true;

            // Assign the changing elements of the previous scanline to
            // prevChangingElems and start putting this new scanline's
            // changing elements into the currChangingElems.
            temp = prevChangingElems;
            prevChangingElems = currChangingElems;
            cce = currChangingElems = temp;
            currIndex = 0;

            // Start decoding the scanline at startX in the raster
            bitOffset = startX;

            // Reset search start position for getNextChangingElement
            lastChangingElement = 0;

            // Till one whole scanline is decoded
            while (bitOffset < w) {
                // Get the next changing element
                getNextChangingElement(a0, isWhite, b);
                b1 = b[0];
                b2 = b[1];

                // Get the next seven bits
                entry = nextLesserThan8Bits(7);
                // Run these through the 2DCodes table
                entry = (int) (twoDCodes[entry] & 0xff);

                // Get the code and the number of bits used up
                code = (entry & 0x78) >>> 3;
                bits = entry & 0x07;

                if (code == 0) { // Pass
                    // We always assume WhiteIsZero format for fax.
                    if (!isWhite) {
                        setToBlack(buffer, lineOffset, bitOffset, b2
                                - bitOffset);
                    }
                    bitOffset = a0 = b2;

                    // Set pointer to only consume the correct number of bits.
                    updatePointer(7 - bits);
                } else if (code == 1) { // Horizontal
                    // Set pointer to only consume the correct number of bits.
                    updatePointer(7 - bits);

                    // identify the next 2 alternating color codes.
                    int number;
                    if (isWhite) {
                        // Following are white and black runs
                        number = decodeWhiteCodeWord();
                        bitOffset += number;
                        cce[currIndex++] = bitOffset;

                        number = decodeBlackCodeWord();
                        setToBlack(buffer, lineOffset, bitOffset, number);
                        bitOffset += number;
                        cce[currIndex++] = bitOffset;
                    } else {
                        // First a black run and then a white run follows
                        number = decodeBlackCodeWord();
                        setToBlack(buffer, lineOffset, bitOffset, number);
                        bitOffset += number;
                        cce[currIndex++] = bitOffset;

                        number = decodeWhiteCodeWord();
                        bitOffset += number;
                        cce[currIndex++] = bitOffset;
                    }

                    a0 = bitOffset;
                } else if (code <= 8) { // Vertical
                    a1 = b1 + (code - 5);
                    cce[currIndex++] = a1;

                    // We write the current color till a1 - 1 pos,
                    // since a1 is where the next color starts
                    if (!isWhite) {
                        setToBlack(buffer, lineOffset, bitOffset, a1
                                - bitOffset);
                    }
                    bitOffset = a0 = a1;
                    isWhite = !isWhite;

                    updatePointer(7 - bits);
                } else if (code == 11) {
                    if (nextLesserThan8Bits(3) != 7) {
                        throw new Error(JaiI18N.getString("XTIFFFaxDecoder5"));
                    }

                    int zeros = 0;
                    boolean exit = false;

                    while (!exit) {
                        while (nextLesserThan8Bits(1) != 1) {
                            zeros++;
                        }

                        if (zeros > 5) {
                            // Exit code

                            // Zeros before exit code
                            zeros = zeros - 6;

                            if (!isWhite && (zeros > 0)) {
                                cce[currIndex++] = bitOffset;
                            }

                            // Zeros before the exit code
                            bitOffset += zeros;
                            if (zeros > 0) {
                                // Some zeros have been written
                                isWhite = true;
                            }

                            // Read in the bit which specifies the color of
                            // the following run
                            if (nextLesserThan8Bits(1) == 0) {
                                if (!isWhite) {
                                    cce[currIndex++] = bitOffset;
                                }
                                isWhite = true;
                            } else {
                                if (isWhite) {
                                    cce[currIndex++] = bitOffset;
                                }
                                isWhite = false;
                            }

                            exit = true;
                        }

                        if (zeros == 5) {
                            if (!isWhite) {
                                cce[currIndex++] = bitOffset;
                            }
                            bitOffset += zeros;

                            // Last thing written was white
                            isWhite = true;
                        } else {
                            bitOffset += zeros;

                            cce[currIndex++] = bitOffset;
                            setToBlack(buffer, lineOffset, bitOffset, 1);
                            ++bitOffset;

                            // Last thing written was black
                            isWhite = false;
                        }

                    }
                } else {
                    throw new Error(JaiI18N.getString("XTIFFFaxDecoder5"));
                }
            }

            // Add the changing element beyond the current scanline for the
            // other color too
            cce[currIndex++] = bitOffset;

            // Number of changing elements in this scanline.
            changingElemSize = currIndex;

            lineOffset += scanlineStride;
        }
    }

    private void setToBlack(byte[] buffer, int lineOffset, int bitOffset,
                            int numBits) {
        int bitNum = 8 * lineOffset + bitOffset;
        int lastBit = bitNum + numBits;