int bits = ilength * iw;    // number of all used bits        byte[] out = new byte[(bits+ow-1)/ow];         // starting from the 0th bit in the input        int ipos = 0;         // the number of padding 0's needed in the output, skip them        int opos = (bits+ow-1)/ow*ow-bits;         while(ipos < bits) {            int count = iw - ipos%iw;   // unpacked bits in current input byte            if (count > ow - opos%ow) { // free space available in output byte                count = ow - opos%ow;   // choose the smaller number            }            // and move them!            out[opos/ow] |=                         // paste!                (((in[ioffset+ipos/iw]+256)         // locate the byte (+256 so that it's never negative)                    >> (iw-ipos%iw-count))          // move to the end of a byte                        & ((1 << (count))-1))       // zero out all other bits                            << (ow-opos%ow-count);  // move to the output position            ipos += count;  // advance            opos += count;  // advance        }        return out;    }     /**     * Repack from NUB 8 to a NUB 7 OID sub-identifier, remove all     * unnecessary 0 headings, set the first bit of all non-tail     * output bytes to 1 (as ITU-T Rec. X.690 8.19.2 says), and     * paste it into an existing byte array.     * @param out the existing array to be pasted into     * @param ooffset the starting position to paste     * @return the number of bytes pasted     */    private static int pack7Oid(byte[] in, int ioffset, int ilength, byte[] out, int ooffset) {        byte[] pack = pack(in, ioffset, ilength, 8, 7);        int firstNonZero = pack.length-1;   // paste at least one byte        for (int i=pack.length-2; i>=0; i--) {            if (pack[i] != 0) {                firstNonZero = i;            }            pack[i] |= 0x80;        }        System.arraycopy(pack, firstNonZero, out, ooffset, pack.length-firstNonZero);        return pack.length-firstNonZero;    }     /**     * Repack from NUB 7 to NUB 8, remove all unnecessary 0     * headings, and paste it into an existing byte array.     * @param out the existing array to be pasted into     * @param ooffset the starting position to paste     * @return the number of bytes pasted     */    private static int pack8(byte[] in, int ioffset, int ilength, byte[] out, int ooffset) {        byte[] pack = pack(in, ioffset, ilength, 7, 8);        int firstNonZero = pack.length-1;   // paste at least one byte        for (int i=pack.length-2; i>=0; i--) {            if (pack[i] != 0) {                firstNonZero = i;            }        }        System.arraycopy(pack, firstNonZero, out, ooffset, pack.length-firstNonZero);        return pack.length-firstNonZero;    }     /**     * Pack the int into a OID sub-identifier DER encoding     */    private static int pack7Oid(int input, byte[] out, int ooffset) {        byte[] b = new byte[4];        b[0] = (byte)(input >> 24);        b[1] = (byte)(input >> 16);        b[2] = (byte)(input >> 8);        b[3] = (byte)(input);        return pack7Oid(b, 0, 4, out, ooffset);    }     /**     * Pack the BigInteger into a OID subidentifier DER encoding     */    private static int pack7Oid(BigInteger input, byte[] out, int ooffset) {        byte[] b = input.toByteArray();        return pack7Oid(b, 0, b.length, out, ooffset);    }     /**     * Private methods to check validity of OID. They must be --     * 1. at least 2 components     * 2. all components must be non-negative     * 3. the first must be 0, 1 or 2     * 4. if the first is 0 or 1, the second must be <40     */     /**     * Check the DER encoding. Since DER encoding defines that the integer bits     * are unsigned, so there's no need to check the MSB.     */    private static void check(byte[] encoding) throws IOException {        int length = encoding.length;        if (length < 1 ||      // too short                (encoding[length - 1] & 0x80) != 0) {  // not ended            throw new IOException("ObjectIdentifier() -- " +                    "Invalid DER encoding, not ended");        }        for (int i=0; i<length; i++) {            // 0x80 at the beginning of a subidentifier            if (encoding[i] == (byte)0x80 &&                    (i==0 || (encoding[i-1] & 0x80) == 0)) {                throw new IOException("ObjectIdentifier() -- " +                        "Invalid DER encoding, useless extra octet detected");            }        }    }    private static void checkCount(int count) throws IOException {        if (count < 2) {            throw new IOException("ObjectIdentifier() -- " +                    "Must be at least two oid components ");        }    }    private static void checkFirstComponent(int first) throws IOException {        if (first < 0 || first > 2) {            throw new IOException("ObjectIdentifier() -- " +                    "First oid component is invalid ");        }    }    private static void checkFirstComponent(BigInteger first) throws IOException {        if (first.signum() == -1 ||                first.compareTo(BigInteger.valueOf(2)) == 1) {            throw new IOException("ObjectIdentifier() -- " +                    "First oid component is invalid ");        }    }    private static void checkSecondComponent(int first, int second) throws IOException {        if (second < 0 || first != 2 && second > 39) {            throw new IOException("ObjectIdentifier() -- " +                    "Second oid component is invalid ");        }    }    private static void checkSecondComponent(int first, BigInteger second) throws IOException {        if (second.signum() == -1 ||                first != 2 &&                second.compareTo(BigInteger.valueOf(39)) == 1) {            throw new IOException("ObjectIdentifier() -- " +                    "Second oid component is invalid ");        }    }    private static void checkOtherComponent(int i, int num) throws IOException {        if (num < 0) {            throw new IOException("ObjectIdentifier() -- " +                    "oid component #" + (i+1) + " must be non-negative ");        }    }    private static void checkOtherComponent(int i, BigInteger num) throws IOException {        if (num.signum() == -1) {            throw new IOException("ObjectIdentifier() -- " +                    "oid component #" + (i+1) + " must be non-negative ");        }    }}

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