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The Bouncy Castle Java APIs for the OpenPGP Protocol. The APIs are designed primarily to be used in conjunction with the BC LTS provider but may also be used with other providers providing cryptographic services.

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package org.bouncycastle.bcpg;

public class CRC24
{
    protected static final int CRC24_INIT = 0x0b704ce;
    protected static final int CRC24_POLY = 0x1864cfb;

    protected int crc = CRC24_INIT;

    /**
     * Default, iterative CRC-24 implementation as described in RFC4880.
     * This implementation mimics the use of a feedback shift register in software.
     *
     * @see 
     * RFC4880 §6.1. An Implementation of the CRC-24 in "C"
     */
    public CRC24()
    {
    }

    public void update(int b)
    {
        crc ^= b << 16;
        for (int i = 0; i < 8; i++)
        {
            int carry = ((crc << 8) >> 31) & CRC24_POLY;
            crc = (crc << 1) ^ carry;
        }
    }

    public void update3(byte[] buf, int off)
    {
        update(buf[off + 0] & 0xFF);
        update(buf[off + 1] & 0xFF);
        update(buf[off + 2] & 0xFF);
    }

    public int getValue()
    {
        return crc & 0xFFFFFF;
    }

    public void reset()
    {
        crc = CRC24_INIT;
    }
}