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

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package org.bouncycastle.util.encoders;


/**
 * A buffering class to allow translation from one format to another to
 * be done in discrete chunks.
 */
public class BufferedDecoder
{
    protected byte[]        buf;
    protected int           bufOff;

    protected Translator    translator;

    /**
     * @param translator the translator to use.
     * @param bufSize amount of input to buffer for each chunk.
     */
    public BufferedDecoder(
        Translator  translator,
        int         bufSize)
    {
        this.translator = translator;

        if ((bufSize % translator.getEncodedBlockSize()) != 0)
        {
            throw new IllegalArgumentException("buffer size not multiple of input block size");
        }

        buf = new byte[bufSize];
        bufOff = 0;
    }

    public int processByte(
        byte        in,
        byte[]      out,
        int         outOff)
    {
        int         resultLen = 0;

        buf[bufOff++] = in;

        if (bufOff == buf.length)
        {
            resultLen = translator.decode(buf, 0, buf.length, out, outOff);
            bufOff = 0;
        }

        return resultLen;
    }

    public int processBytes(
        byte[]      in,
        int         inOff,
        int         len,
        byte[]      out,
        int         outOff)
    {
        if (len < 0)
        {
            throw new IllegalArgumentException("Can't have a negative input length!");
        }

        int resultLen = 0;
        int gapLen = buf.length - bufOff;

        if (len > gapLen)
        {
            System.arraycopy(in, inOff, buf, bufOff, gapLen);

            resultLen += translator.decode(buf, 0, buf.length, out, outOff);

            bufOff = 0;

            len -= gapLen;
            inOff += gapLen;
            outOff += resultLen;

            int chunkSize = len - (len % buf.length);

            resultLen += translator.decode(in, inOff, chunkSize, out, outOff);

            len -= chunkSize;
            inOff += chunkSize;
        }

        if (len != 0)
        {
            System.arraycopy(in, inOff, buf, bufOff, len);

            bufOff += len;
        }

        return resultLen;
    }
}