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package java.util.zip;

import java.nio.ByteBuffer;
import sun.nio.ch.DirectBuffer;

A class that can be used to compute the CRC-32 of a data stream.
 Passing a null argument to a method in this class will cause a NullPointerException to be thrown. 
Author:
     David Connelly
See Also:
Checksum/**
 * A class that can be used to compute the CRC-32 of a data stream.
 *
 * <p> Passing a {@code null} argument to a method in this class will cause
 * a {@link NullPointerException} to be thrown.
 *
 * @see         Checksum
 * @author      David Connelly
 */
public
class CRC32 implements Checksum {
    private int crc;

    
Creates a new CRC32 object.
/**
     * Creates a new CRC32 object.
     */
    public CRC32() {
    }


    
Updates the CRC-32 checksum with the specified byte (the low
eight bits of the argument b).
Params:
b – the byte to update the checksum with/**
     * Updates the CRC-32 checksum with the specified byte (the low
     * eight bits of the argument b).
     *
     * @param b the byte to update the checksum with
     */
    public void update(int b) {
        crc = update(crc, b);
    }

    
Updates the CRC-32 checksum with the specified array of bytes.
Throws:
ArrayIndexOutOfBoundsException –  if off is negative, or len is negative, or off+len is greater than the length of the array b/**
     * Updates the CRC-32 checksum with the specified array of bytes.
     *
     * @throws  ArrayIndexOutOfBoundsException
     *          if {@code off} is negative, or {@code len} is negative,
     *          or {@code off+len} is greater than the length of the
     *          array {@code b}
     */
    public void update(byte[] b, int off, int len) {
        if (b == null) {
            throw new NullPointerException();
        }
        if (off < 0 || len < 0 || off > b.length - len) {
            throw new ArrayIndexOutOfBoundsException();
        }
        crc = updateBytes(crc, b, off, len);
    }

    
Updates the CRC-32 checksum with the specified array of bytes.
Params:
b – the array of bytes to update the checksum with/**
     * Updates the CRC-32 checksum with the specified array of bytes.
     *
     * @param b the array of bytes to update the checksum with
     */
    public void update(byte[] b) {
        crc = updateBytes(crc, b, 0, b.length);
    }

    
Updates the checksum with the bytes from the specified buffer. The checksum is updated using buffer.remaining() bytes starting at buffer.position() Upon return, the buffer's position will be updated to its limit; its limit will not have been changed. 
Params:
buffer – the ByteBuffer to update the checksum with
Since:
1.8/**
     * Updates the checksum with the bytes from the specified buffer.
     *
     * The checksum is updated using
     * buffer.{@link java.nio.Buffer#remaining() remaining()}
     * bytes starting at
     * buffer.{@link java.nio.Buffer#position() position()}
     * Upon return, the buffer's position will
     * be updated to its limit; its limit will not have been changed.
     *
     * @param buffer the ByteBuffer to update the checksum with
     * @since 1.8
     */
    public void update(ByteBuffer buffer) {
        int pos = buffer.position();
        int limit = buffer.limit();
        assert (pos <= limit);
        int rem = limit - pos;
        if (rem <= 0)
            return;
        if (buffer instanceof DirectBuffer) {
            crc = updateByteBuffer(crc, ((DirectBuffer)buffer).address(), pos, rem);
        } else if (buffer.hasArray()) {
            crc = updateBytes(crc, buffer.array(), pos + buffer.arrayOffset(), rem);
        } else {
            byte[] b = new byte[rem];
            buffer.get(b);
            crc = updateBytes(crc, b, 0, b.length);
        }
        buffer.position(limit);
    }

    
Resets CRC-32 to initial value.
/**
     * Resets CRC-32 to initial value.
     */
    public void reset() {
        crc = 0;
    }

    
Returns CRC-32 value.
/**
     * Returns CRC-32 value.
     */
    public long getValue() {
        return (long)crc & 0xffffffffL;
    }

    private native static int update(int crc, int b);
    private native static int updateBytes(int crc, byte[] b, int off, int len);

    private native static int updateByteBuffer(int adler, long addr,
                                               int off, int len);
}