/*

 * Copyright (c) 1996, 2020, Oracle and/or its affiliates. All rights reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Oracle designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Oracle in the LICENSE file that accompanied this code.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

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 */

package java.util.zip;

import java.lang.ref.Reference;

import java.nio.ByteBuffer;

import sun.nio.ch.DirectBuffer;

import jdk.internal.vm.annotation.IntrinsicCandidate;

/**

 * A class that can be used to compute the Adler-32 checksum of a data

 * stream. An Adler-32 checksum is almost as reliable as a CRC-32 but

 * can be computed much faster.

 *

 * <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 Adler32 implements Checksum {

    private int adler = 1;

    /**

     * Creates a new Adler32 object.

     */

    public Adler32() {

    }

    /**

     * Updates the checksum with the specified byte (the low eight

     * bits of the argument b).

     */

    @Override

    public void update(int b) {

        adler = update(adler, b);

    }

    /**

     * Updates the 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();

        }

        adler = updateBytes(adler, b, off, len);

    }

    /**

     * Updates the 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.isDirect()) {

            try {

                adler = updateByteBuffer(adler, ((DirectBuffer)buffer).address(), pos, rem);

            } finally {

                Reference.reachabilityFence(buffer);

            }

        } else if (buffer.hasArray()) {

            adler = updateBytes(adler, 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 the checksum to initial value.

     */

    @Override

    public void reset() {

        adler = 1;

    }

    /**

     * Returns the checksum value.

     */

    @Override

    public long getValue() {

        return (long)adler & 0xffffffffL;

    }

    private static native int update(int adler, int b);

    @IntrinsicCandidate

    private static native int updateBytes(int adler, byte[] b, int off,

                                          int len);

    @IntrinsicCandidate

    private static native int updateByteBuffer(int adler, long addr,

                                               int off, int len);

    static {

        ZipUtils.loadLibrary();

    }

}