CRC32クラスはCRC32チェックサムを計算するChecksumインタフェースを実装したクラスである。デフォルトコンストラクタが宣言されているが，実装コードは空である。インスタンス変数としてint型のcrcが宣言されている。
reset()メソッドでは，インスタンス変数crcに0を代入している。またgetValue()メソッドでは，0xffffffffLとcrcをAND演算してcrcの4バイトをlong型で返している。unsigned int型をサポートしていないが故の苦肉の策のように読める。
update(int crc, int b)メソッドとupdateByteBuffer0(int alder, long addr, int off, int len)がこのクラスの本質的な部分であるが，nativeという修飾子がついており，ネイティブコードで実装されていることを示している。updateBytesCheck()メソッドや，updateByteBuffer()メソッドなどはこれらのネイティブメソッドを呼び出している。
ソースコードの最後にstaticイニシャライザが置かれていて，ZipUtilsクラスのstaticメソッドloadLibrary()を実行している。
/*
* Copyright (c) 1996, 2014, 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
* or visit www.oracle.com if you need additional information or have any
* questions.
*/
package java.util.zip;
import java.nio.ByteBuffer;
import java.util.Objects;
import sun.nio.ch.DirectBuffer;
import jdk.internal.HotSpotIntrinsicCandidate;
public
class CRC32 implements Checksum {
private int crc;
public CRC32() {
}
@Override
public void update(int b) {
crc = update(crc, 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);
}
@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);
}
@Override
public void reset() {
crc = 0;
}
@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();
}
}
* Copyright (c) 1996, 2014, 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
* or visit www.oracle.com if you need additional information or have any
* questions.
*/
package java.util.zip;
import java.nio.ByteBuffer;
import java.util.Objects;
import sun.nio.ch.DirectBuffer;
import jdk.internal.HotSpotIntrinsicCandidate;
public
class CRC32 implements Checksum {
private int crc;
public CRC32() {
}
@Override
public void update(int b) {
crc = update(crc, 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);
}
@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);
}
@Override
public void reset() {
crc = 0;
}
@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();
}
}
ＪＹ情報システムズ 