1 files changed, 84 insertions, 0 deletions
diff --git a/src/javaFlacEncoder/CRC16.java b/src/javaFlacEncoder/CRC16.java
new file mode 100644
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--- /dev/null
+++ b/src/javaFlacEncoder/CRC16.java
@@ -0,0 +1,84 @@
+/*
+ * Copyright (C) 2010  Preston Lacey http://javaflacencoder.sourceforge.net/
+ * All Rights Reserved.
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library 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
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
+ */
+
+package javaFlacEncoder;
+
+/**
+ * Class to calculate a CRC16 checksum.
+ * @author Preston Lacey
+ */
+public class CRC16 {
+  /** For Debugging: Higher level equals more debug statements */
+  public static int DEBUG_LEV = 0;
+
+  /** CRC Divisor: 0x8005(implicit 1 at MSB for 0x18005) */
+  static final int divisorCRC16 = 0x8005;
+
+  /** working checksum stored between calls to update(..) */
+  protected int workingCRC;
+
+  private static final short xorTable[] = generateTable();
+
+  /**
+   * Constructor. Creates a CRC16 object that is ready to be used. Next step
+   * would be to call update(...) with appropriate data.
+   */
+  public CRC16() {
+    reset();
+  }
+
+  /**
+   * Resets stored data, preparing object for a new checksum.
+   */
+  public void reset() {
+    workingCRC = 0;
+  }
+
+  public short checksum() {
+    return (short)(workingCRC & 0xFFFF);
+  }
+
+  public int update(byte input) {
+    workingCRC = (workingCRC << 8)^xorTable[((workingCRC >>> 8)^input) & 0xFF];
+    return workingCRC;
+  }
+
+  public int update(byte[] input, int start, int stop) {
+    for(int i = start; i < stop; i++) {
+      byte b = input[i];
+      workingCRC = (workingCRC << 8) ^ xorTable[((workingCRC >>> 8)^b) & 0xFF];
+    }
+    return workingCRC;
+  }
+
+  private static short[] generateTable() {
+    short[] table = new short[256];
+    for(int i = 0; i < table.length; i++) {
+      int polynomial = divisorCRC16;
+      int xorVal = i << 8;
+      int topmask = 1 << 16;
+      for(int x = 0; x < 8; x++ ) {
+        xorVal = xorVal << 1;
+        if( (xorVal & topmask) > 0) xorVal = (xorVal) ^ polynomial;
+      }
+      table[i] = (short)(xorVal & 0xFFFF);
+    }
+    return table;
+  }
+}