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The Bouncy Castle Crypto package is a Java implementation of cryptographic algorithms. This jar contains JCE provider for the Bouncy Castle Cryptography APIs for JDK 1.5 to JDK 1.7.

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package org.spongycastle.asn1;

import java.io.IOException;
import java.io.OutputStream;

/**
 * Stream that produces output based on the default encoding for the passed in objects.
 */
public class ASN1OutputStream
{
    private OutputStream os;

    public ASN1OutputStream(
        OutputStream    os)
    {
        this.os = os;
    }

    void writeLength(
        int length)
        throws IOException
    {
        if (length > 127)
        {
            int size = 1;
            int val = length;

            while ((val >>>= 8) != 0)
            {
                size++;
            }

            write((byte)(size | 0x80));

            for (int i = (size - 1) * 8; i >= 0; i -= 8)
            {
                write((byte)(length >> i));
            }
        }
        else
        {
            write((byte)length);
        }
    }

    void write(int b)
        throws IOException
    {
        os.write(b);
    }

    void write(byte[] bytes)
        throws IOException
    {
        os.write(bytes);
    }

    void write(byte[] bytes, int off, int len)
        throws IOException
    {
        os.write(bytes, off, len);
    }

    void writeEncoded(
        int     tag,
        byte[]  bytes)
        throws IOException
    {
        write(tag);
        writeLength(bytes.length);
        write(bytes);
    }

    void writeTag(int flags, int tagNo)
        throws IOException
    {
        if (tagNo < 31)
        {
            write(flags | tagNo);
        }
        else
        {
            write(flags | 0x1f);
            if (tagNo < 128)
            {
                write(tagNo);
            }
            else
            {
                byte[] stack = new byte[5];
                int pos = stack.length;

                stack[--pos] = (byte)(tagNo & 0x7F);

                do
                {
                    tagNo >>= 7;
                    stack[--pos] = (byte)(tagNo & 0x7F | 0x80);
                }
                while (tagNo > 127);

                write(stack, pos, stack.length - pos);
            }
        }
    }

    void writeEncoded(int flags, int tagNo, byte[] bytes)
        throws IOException
    {
        writeTag(flags, tagNo);
        writeLength(bytes.length);
        write(bytes);
    }

    protected void writeNull()
        throws IOException
    {
        os.write(BERTags.NULL);
        os.write(0x00);
    }

    public void writeObject(
        ASN1Encodable obj)
        throws IOException
    {
        if (obj != null)
        {
            obj.toASN1Primitive().encode(this);
        }
        else
        {
            throw new IOException("null object detected");
        }
    }

    void writeImplicitObject(ASN1Primitive obj)
        throws IOException
    {
        if (obj != null)
        {
            obj.encode(new ImplicitOutputStream(os));
        }
        else
        {
            throw new IOException("null object detected");
        }
    }

    public void close()
        throws IOException
    {
        os.close();
    }

    public void flush()
        throws IOException
    {
        os.flush();
    }

    ASN1OutputStream getDERSubStream()
    {
        return new DEROutputStream(os);
    }

    ASN1OutputStream getDLSubStream()
    {
        return new DLOutputStream(os);
    }

    private class ImplicitOutputStream
        extends ASN1OutputStream
    {
        private boolean first = true;

        public ImplicitOutputStream(OutputStream os)
        {
            super(os);
        }

        public void write(int b)
            throws IOException
        {
            if (first)
            {
                first = false;
            }
            else
            {
                super.write(b);
            }
        }
    }
}