Initial revision

From-SVN: r102074

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); }
+}