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authorupstream source tree <ports@midipix.org>2015-03-15 20:14:05 -0400
committerupstream source tree <ports@midipix.org>2015-03-15 20:14:05 -0400
commit554fd8c5195424bdbcabf5de30fdc183aba391bd (patch)
tree976dc5ab7fddf506dadce60ae936f43f58787092 /libjava/classpath/java/util/zip/CRC32.java
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+/* CRC32.java - Computes CRC32 data checksum of a data stream
+ Copyright (C) 1999. 2000, 2001 Free Software Foundation, Inc.
+
+This file is part of GNU Classpath.
+
+GNU Classpath is free software; you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation; either version 2, or (at your option)
+any later version.
+
+GNU Classpath 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 for more details.
+
+You should have received a copy of the GNU General Public License
+along with GNU Classpath; see the file COPYING. If not, write to the
+Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+02110-1301 USA.
+
+Linking this library statically or dynamically with other modules is
+making a combined work based on this library. Thus, the terms and
+conditions of the GNU General Public License cover the whole
+combination.
+
+As a special exception, the copyright holders of this library give you
+permission to link this library with independent modules to produce an
+executable, regardless of the license terms of these independent
+modules, and to copy and distribute the resulting executable under
+terms of your choice, provided that you also meet, for each linked
+independent module, the terms and conditions of the license of that
+module. An independent module is a module which is not derived from
+or based on this library. If you modify this library, you may extend
+this exception to your version of the library, but you are not
+obligated to do so. If you do not wish to do so, delete this
+exception statement from your version. */
+
+package java.util.zip;
+
+/*
+ * Written using on-line Java Platform 1.2 API Specification, as well
+ * as "The Java Class Libraries", 2nd edition (Addison-Wesley, 1998).
+ * The actual CRC32 algorithm is taken from RFC 1952.
+ * Status: Believed complete and correct.
+ */
+
+/**
+ * Computes CRC32 data checksum of a data stream.
+ * The actual CRC32 algorithm is described in RFC 1952
+ * (GZIP file format specification version 4.3).
+ * Can be used to get the CRC32 over a stream if used with checked input/output
+ * streams.
+ *
+ * @see InflaterInputStream
+ * @see DeflaterOutputStream
+ *
+ * @author Per Bothner
+ * @date April 1, 1999.
+ */
+public class CRC32 implements Checksum
+{
+ /** The crc data checksum so far. */
+ private int crc = 0;
+
+ /** The fast CRC table. Computed once when the CRC32 class is loaded. */
+ private static int[] crc_table = make_crc_table();
+
+ /** Make the table for a fast CRC. */
+ private static int[] make_crc_table ()
+ {
+ int[] crc_table = new int[256];
+ for (int n = 0; n < 256; n++)
+ {
+ int c = n;
+ for (int k = 8; --k >= 0; )
+ {
+ if ((c & 1) != 0)
+ c = 0xedb88320 ^ (c >>> 1);
+ else
+ c = c >>> 1;
+ }
+ crc_table[n] = c;
+ }
+ return crc_table;
+ }
+
+ /**
+ * Returns the CRC32 data checksum computed so far.
+ */
+ public long getValue ()
+ {
+ return (long) crc & 0xffffffffL;
+ }
+
+ /**
+ * Resets the CRC32 data checksum as if no update was ever called.
+ */
+ public void reset () { crc = 0; }
+
+ /**
+ * Updates the checksum with the int bval.
+ *
+ * @param bval (the byte is taken as the lower 8 bits of bval)
+ */
+
+ public void update (int bval)
+ {
+ int c = ~crc;
+ c = crc_table[(c ^ bval) & 0xff] ^ (c >>> 8);
+ crc = ~c;
+ }
+
+ /**
+ * Adds the byte array to the data checksum.
+ *
+ * @param buf the buffer which contains the data
+ * @param off the offset in the buffer where the data starts
+ * @param len the length of the data
+ */
+ public void update (byte[] buf, int off, int len)
+ {
+ int c = ~crc;
+ while (--len >= 0)
+ c = crc_table[(c ^ buf[off++]) & 0xff] ^ (c >>> 8);
+ crc = ~c;
+ }
+
+ /**
+ * Adds the complete byte array to the data checksum.
+ */
+ public void update (byte[] buf) { update(buf, 0, buf.length); }
+}