xtifffaxdecoder.java

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        int byteNum = bitNum >> 3;

        // Handle bits in first byte
        int shift = bitNum & 0x7;
        if (shift > 0) {
            int maskVal = 1 << (7 - shift);
            byte val = buffer[byteNum];
            while (maskVal > 0 && bitNum < lastBit) {
                val |= maskVal;
                maskVal >>= 1;
                ++bitNum;
            }
            buffer[byteNum] = val;
        }

        // Fill in 8 bits at a time
        byteNum = bitNum >> 3;
        while (bitNum < lastBit - 7) {
            buffer[byteNum++] = (byte) 255;
            bitNum += 8;
        }

        // Fill in remaining bits
        while (bitNum < lastBit) {
            byteNum = bitNum >> 3;
            buffer[byteNum] |= 1 << (7 - (bitNum & 0x7));
            ++bitNum;
        }
    }

    // Returns run length
    private int decodeWhiteCodeWord() {
        int current, entry, bits, isT, twoBits, code = -1;
        int runLength = 0;
        boolean isWhite = true;

        while (isWhite) {
            current = nextNBits(10);
            entry = white[current];

            // Get the 3 fields from the entry
            isT = entry & 0x0001;
            bits = (entry >>> 1) & 0x0f;

            if (bits == 12) { // Additional Make up code
                // Get the next 2 bits
                twoBits = nextLesserThan8Bits(2);
                // Consolidate the 2 new bits and last 2 bits into 4 bits
                current = ((current << 2) & 0x000c) | twoBits;
                entry = additionalMakeup[current];
                bits = (entry >>> 1) & 0x07; // 3 bits 0000 0111
                code = (entry >>> 4) & 0x0fff; // 12 bits
                runLength += code;
                updatePointer(4 - bits);
            } else if (bits == 0) { // ERROR
                throw new Error(JaiI18N.getString("XTIFFFaxDecoder0"));
            } else if (bits == 15) { // EOL
                throw new Error(JaiI18N.getString("XTIFFFaxDecoder1"));
            } else {
                // 11 bits - 0000 0111 1111 1111 = 0x07ff
                code = (entry >>> 5) & 0x07ff;
                runLength += code;
                updatePointer(10 - bits);
                if (isT == 0) {
                    isWhite = false;
                }
            }
        }

        return runLength;
    }

    // Returns run length
    private int decodeBlackCodeWord() {
        int current, entry, bits, isT, twoBits, code = -1;
        int runLength = 0;
        boolean isWhite = false;

        while (!isWhite) {
            current = nextLesserThan8Bits(4);
            entry = initBlack[current];

            // Get the 3 fields from the entry
            isT = entry & 0x0001;
            bits = (entry >>> 1) & 0x000f;
            code = (entry >>> 5) & 0x07ff;

            if (code == 100) {
                current = nextNBits(9);
                entry = black[current];

                // Get the 3 fields from the entry
                isT = entry & 0x0001;
                bits = (entry >>> 1) & 0x000f;
                code = (entry >>> 5) & 0x07ff;

                if (bits == 12) {
                    // Additional makeup codes
                    updatePointer(5);
                    current = nextLesserThan8Bits(4);
                    entry = additionalMakeup[current];
                    bits = (entry >>> 1) & 0x07; // 3 bits 0000 0111
                    code = (entry >>> 4) & 0x0fff; // 12 bits
                    runLength += code;

                    updatePointer(4 - bits);
                } else if (bits == 15) {
                    // EOL code
                    throw new Error(JaiI18N.getString("XTIFFFaxDecoder2"));
                } else {
                    runLength += code;
                    updatePointer(9 - bits);
                    if (isT == 0) {
                        isWhite = true;
                    }
                }
            } else if (code == 200) {
                // Is a Terminating code
                current = nextLesserThan8Bits(2);
                entry = twoBitBlack[current];
                code = (entry >>> 5) & 0x07ff;
                runLength += code;
                bits = (entry >>> 1) & 0x0f;
                updatePointer(2 - bits);
                isWhite = true;
            } else {
                // Is a Terminating code
                runLength += code;
                updatePointer(4 - bits);
                isWhite = true;
            }
        }

        return runLength;
    }

    private int readEOL() {
        if (fillBits == 0) {
            if (nextNBits(12) != 1) {
                throw new Error(JaiI18N.getString("XTIFFFaxDecoder6"));
            }
        } else if (fillBits == 1) {

            // First EOL code word xxxx 0000 0000 0001 will occur
            // As many fill bits will be present as required to make
            // the EOL code of 12 bits end on a byte boundary.

            int bitsLeft = 8 - bitPointer;

            if (nextNBits(bitsLeft) != 0) {
                throw new Error(JaiI18N.getString("XTIFFFaxDecoder8"));
            }

            // If the number of bitsLeft is less than 8, then to have a 12
            // bit EOL sequence, two more bytes are certainly going to be
            // required. The first of them has to be all zeros, so ensure
            // that.
            if (bitsLeft < 4) {
                if (nextNBits(8) != 0) {
                    throw new Error(JaiI18N.getString("XTIFFFaxDecoder8"));
                }
            }

            // There might be a random number of fill bytes with 0s, so
            // loop till the EOL of 0000 0001 is found, as long as all
            // the bytes preceding it are 0's.
            int n;
            while ((n = nextNBits(8)) != 1) {

                // If not all zeros
                if (n != 0) {
                    throw new Error(JaiI18N.getString("XTIFFFaxDecoder8"));
                }
            }
        }

        // If one dimensional encoding mode, then always return 1
        if (oneD == 0) {
            return 1;
        } else {
            // Otherwise for 2D encoding mode,
            // The next one bit signifies 1D/2D encoding of next line.
            return nextLesserThan8Bits(1);
        }
    }

    private void getNextChangingElement(int a0, boolean isWhite, int[] ret) {
        // Local copies of instance variables
        int[] pce = this.prevChangingElems;
        int ces = this.changingElemSize;

        // If the previous match was at an odd element, we still
        // have to search the preceeding element.
        // int start = lastChangingElement & ~0x1;
        int start = lastChangingElement > 0 ? lastChangingElement - 1 : 0;
        if (isWhite) {
            start &= ~0x1; // Search even numbered elements
        } else {
            start |= 0x1; // Search odd numbered elements
        }

        int i = start;
        for (; i < ces; i += 2) {
            int temp = pce[i];
            if (temp > a0) {
                lastChangingElement = i;
                ret[0] = temp;
                break;
            }
        }

        if (i + 1 < ces) {
            ret[1] = pce[i + 1];
        }
    }

    private int nextNBits(int bitsToGet) {
        byte b, next, next2next;
        int l = data.length - 1;
        int bp = this.bytePointer;

        if (fillOrder == 1) {
            b = data[bp];

            if (bp == l) {
                next = 0x00;
                next2next = 0x00;
            } else if ((bp + 1) == l) {
                next = data[bp + 1];
                next2next = 0x00;
            } else {
                next = data[bp + 1];
                next2next = data[bp + 2];
            }
        } else if (fillOrder == 2) {
            b = flipTable[data[bp] & 0xff];

            if (bp == l) {
                next = 0x00;
                next2next = 0x00;
            } else if ((bp + 1) == l) {
                next = flipTable[data[bp + 1] & 0xff];
                next2next = 0x00;
            } else {
                next = flipTable[data[bp + 1] & 0xff];
                next2next = flipTable[data[bp + 2] & 0xff];
            }
        } else {
            throw new Error(JaiI18N.getString("XTIFFFaxDecoder7"));
        }

        int bitsLeft = 8 - bitPointer;
        int bitsFromNextByte = bitsToGet - bitsLeft;
        int bitsFromNext2NextByte = 0;
        if (bitsFromNextByte > 8) {
            bitsFromNext2NextByte = bitsFromNextByte - 8;
            bitsFromNextByte = 8;
        }

        bytePointer++;

        int i1 = (b & table1[bitsLeft]) << (bitsToGet - bitsLeft);
        int i2 = (next & table2[bitsFromNextByte]) >>> (8 - bitsFromNextByte);

        int i3 = 0;
        if (bitsFromNext2NextByte != 0) {
            i2 <<= bitsFromNext2NextByte;
            i3 = (next2next & table2[bitsFromNext2NextByte]) >>> (8 - bitsFromNext2NextByte);
            i2 |= i3;
            bytePointer++;
            bitPointer = bitsFromNext2NextByte;
        } else {
            if (bitsFromNextByte == 8) {
                bitPointer = 0;
                bytePointer++;
            } else {
                bitPointer = bitsFromNextByte;
            }
        }

        int i = i1 | i2;
        return i;
    }

    private int nextLesserThan8Bits(int bitsToGet) {
        byte b, next;
        int l = data.length - 1;
        int bp = this.bytePointer;

        if (fillOrder == 1) {
            b = data[bp];
            if (bp == l) {
                next = 0x00;
            } else {
                next = data[bp + 1];
            }
        } else if (fillOrder == 2) {
            b = flipTable[data[bp] & 0xff];
            if (bp == l) {
                next = 0x00;
            } else {
                next = flipTable[data[bp + 1] & 0xff];
            }
        } else {
            throw new Error(JaiI18N.getString("XTIFFFaxDecoder7"));
        }

        int bitsLeft = 8 - bitPointer;
        int bitsFromNextByte = bitsToGet - bitsLeft;

        int shift = bitsLeft - bitsToGet;
        int i1, i2;
        if (shift >= 0) {
            i1 = (b & table1[bitsLeft]) >>> shift;
            bitPointer += bitsToGet;
            if (bitPointer == 8) {
                bitPointer = 0;
                bytePointer++;
            }
        } else {
            i1 = (b & table1[bitsLeft]) << (-shift);
            i2 = (next & table2[bitsFromNextByte]) >>> (8 - bitsFromNextByte);

            i1 |= i2;
            bytePointer++;
            bitPointer = bitsFromNextByte;
        }

        return i1;
    }

    // Move pointer backwards by given amount of bits
    private void updatePointer(int bitsToMoveBack) {
        int i = bitPointer - bitsToMoveBack;

        if (i < 0) {
            bytePointer--;
            bitPointer = 8 + i;
        } else {
            bitPointer = i;
        }
    }

    // Move to the next byte boundary
    private boolean advancePointer() {
        if (bitPointer != 0) {
            bytePointer++;
            bitPointer = 0;
        }

        return true;
    }
}