[freenet-cvs] r17694 - trunk/freenet/src/freenet/support

[nextgens at freenetproject.org]

Author: nextgens
Date: 2008-02-08 11:09:14 +0000 (Fri, 08 Feb 2008)
New Revision: 17694

Added:
   trunk/freenet/src/freenet/support/CRC.java
Log:
A new class in freenet.support to compute CRCs. I will use it in the PNG filter

Added: trunk/freenet/src/freenet/support/CRC.java
===================================================================
--- trunk/freenet/src/freenet/support/CRC.java	                        (rev 0)
+++ trunk/freenet/src/freenet/support/CRC.java	2008-02-08 11:09:14 UTC (rev 17694)
@@ -0,0 +1,44 @@
+/* This code is part of Freenet. It is distributed under the GNU General
+ * Public License, version 2 (or at your option any later version). See
+ * http://www.gnu.org/ for further details of the GPL. */
+package freenet.support;
+
+/**
+ * A class to compute CRCs complying with ISO 3309
+ * It's used in the PNG filter.
+ * 
+ * @author nextgens
+ */
+public class CRC {
+	public static final long[] CRC_TABLE = new long[256];
+	public static final long PNG_POLYNOMINAL = 0xedb88320L;
+	
+	static {
+		long c;
+		for(int i=0; i<256; i++) {
+			c = i;
+			for(int j=0; j<8; j++) {
+				if(0 != (c & 1))
+					c = PNG_POLYNOMINAL^(c >> 1);
+				else
+					c = c >> 1;
+			}
+			CRC_TABLE[i] = c;
+		}
+	}
+	
+	private static long update_crc(long crc, byte[] buf) {
+		// it can't be above 2^31-1 anyway... hence we use an int
+		if(buf.length > Integer.MAX_VALUE)
+			throw new IllegalArgumentException("The buffer is too big!");
+		
+		for (int i = 0; i < buf.length; i++)
+			crc = CRC_TABLE[(int)(crc ^ buf[i]) & 0xff] ^ (crc >> 8);
+		
+		return crc;
+	}
+	
+	public static long crc(byte[] input) {
+		return update_crc(0xffffffffL, input) ^ 0xffffffffL;
+	}
+}