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package java.util.zip;

import java.nio.ByteBuffer;
import java.util.Objects;

import sun.nio.ch.DirectBuffer;
import jdk.internal.HotSpotIntrinsicCandidate;

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
Since:
1.1/**
 * 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.</p>
 *
 * @author      David Connelly
 * @since 1.1
 */
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).
/**
     * Updates the CRC-32 checksum with the specified byte (the low
     * eight bits of the argument b).
     */
    @Override
    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 negative or 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 negative or greater than the length of
     *         the array {@code b}.
     */
    @Override
    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 bytes from the specified buffer.
The checksum is updated with the remaining bytes in the buffer, starting
at the buffer's position. Upon return, the buffer's position will be
updated to its limit; its limit will not have been changed.
Since:
1.8/**
     * Updates the CRC-32 checksum with the bytes from the specified buffer.
     *
     * The checksum is updated with the remaining bytes in the buffer, starting
     * at the buffer's position. Upon return, the buffer's position will be
     * updated to its limit; its limit will not have been changed.
     *
     * @since 1.8
     */
    @Override
    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[Math.min(buffer.remaining(), 4096)];
            while (buffer.hasRemaining()) {
                int length = Math.min(buffer.remaining(), b.length);
                buffer.get(b, 0, length);
                update(b, 0, length);
            }
        }
        buffer.position(limit);
    }

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

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

    @HotSpotIntrinsicCandidate
    private static native int update(int crc, int b);

    private static int updateBytes(int crc, byte[] b, int off, int len) {
        updateBytesCheck(b, off, len);
        return updateBytes0(crc, b, off, len);
    }

    @HotSpotIntrinsicCandidate
    private static native int updateBytes0(int crc, byte[] b, int off, int len);

    private static void updateBytesCheck(byte[] b, int off, int len) {
        if (len <= 0) {
            return;  // not an error because updateBytesImpl won't execute if len <= 0
        }

        Objects.requireNonNull(b);

        if (off < 0 || off >= b.length) {
            throw new ArrayIndexOutOfBoundsException(off);
        }

        int endIndex = off + len - 1;
        if (endIndex < 0 || endIndex >= b.length) {
            throw new ArrayIndexOutOfBoundsException(endIndex);
        }
    }

    private static int updateByteBuffer(int alder, long addr,
                                        int off, int len) {
        updateByteBufferCheck(addr);
        return updateByteBuffer0(alder, addr, off, len);
    }

    @HotSpotIntrinsicCandidate
    private static native int updateByteBuffer0(int alder, long addr,
                                                int off, int len);

    private static void updateByteBufferCheck(long addr) {
        // Performs only a null check because bounds checks
        // are not easy to do on raw addresses.
        if (addr == 0L) {
            throw new NullPointerException();
        }
    }

    static {
        ZipUtils.loadLibrary();
    }
}