package Tools;
import java.io.*;

/**
 * 
 * Computes 32-bit Cyclic Redundancy Checks. Allows the use of
 * arbitrary polynomials.<p>
 * 
 * Source: The core CRC computation (update()) and the buildTable
 * routine are based on those in a public-domain Pascal program called
 * "CRC_Calc" by F. Martin Richardson, Jr. I found his code at
 * http://www.csd.net/~cgadd/knowbase/CRC0019.HTM Excerpted comments
 * from his program:
 *
 * Routines for calculations derived with the help of Doctor Dobb's Journal
 * #188, MAY 1992.
 * ...
 * This file is hereby commited to the public domain.  Feel free to use it in
 * your development.  All I ask is a little recognition if you use it in your
 * software.  Also, if this file is modified in any way and re-distributed,
 * please retain the credits to the people who wrote the routines.
 *
 * @license This code is Copyright 1999 Jon Howell. It is available for
 * use under the GNU Public License, available at:
 * http://www.gnu.org/copyleft/gpl.html
 * @author Jon Howell <jonh@cs.dartmouth.edu>
 * @rcs $Id: CRC32.java,v 1.2 2000/05/22 01:32:25 jonh Exp $
 */
public class CRC32
	implements java.util.zip.Checksum {

	// a quickie static method to compute the CRC of a single array
	// without explicitly allocating a CRC32 object in the client's code
	public static long crc32(byte[] s)
	{
		CRC32 crc = new CRC32();
		crc.update(s);
		return crc.getValue();
	}

	// if you need to compute a running CRC, instantiate a CRC32
	// object and keep updating it with it arrays. When you're done, ask it
	// for its value.

	// create a CRC32 accumulator object
	public CRC32() {
		crcTable = crcTable_edb88320;
		reset();
	}

	// create a CRC32 accumulator with a custom polynomial
	public CRC32(int polynomial) {
		// TODO: if someone actually uses this class regularly with
		// some other polynomial, they should either (a) make a prototype
		// instance of CRC32 and clone() it, or (b) I should support
		// some way of caching runtime-generated polynomial tables.
		crcTable = buildTable(polynomial);
		reset();
	}

	public void reset() {
		crcValue = 0;
	}

	public void update(int b) {
		// can't imagine this being a really popular routine;
		// it's here to satisfy the java.util.zip.Checksum interface.
		crcValue = crcTable[(crcValue ^ b) & 0xff] ^ (crcValue >>> 8);
	}

	public void update(byte[] s) {
		update(s, 0, s.length);
	}

	public void update(byte[] s, int off, int len) {
		for (int i=off;  i<len;  i++) {
			// if we were sure the compiler would inline, we would call
			// update(int b).
			crcValue = (crcValue >>> 8) ^ crcTable[(crcValue ^ s[i]) & 0xff];
		}
	}

	public long getValue() {
		return crcValue;
	}

	// instance variables
	int crcValue;
	int crcTable[];

	// This main method lets you do one of these things from the command line:
	//	- build a CRC32 table
	//	- compute the CRC32 of System.in
	// You may speficy which polynomial to use with a -polynomial argument.
	//
	public static void main(String args[]) {
		int offset = -1;
		int crcPolynomial = 0xedb88320;
		while (args.length-offset > 1) {
			offset++;
			if (args[offset].equals("-polynomial")) {
				if (args.length-offset > 1) {
					offset++;
					crcPolynomial = (int) (Long.parseLong(args[offset], 16));
				} else {
					usage();
					return;
				}
			} else if (args[offset].equals("-buildTable")) {
				printTable(crcPolynomial);
				return;
			} else {	
				usage();
				return;
			}
		}

		int rc;
		int len=0;
		byte buf[] = new byte[397]; // arbitrary buffer length just for kicks
		CRC32 crc = new CRC32(crcPolynomial);

		try {
			while ((rc = System.in.read(buf, 0, 397)) > 0) {
				crc.update(buf, 0, rc);
				len += rc;
			}
		} catch (IOException ex) {
			ex.printStackTrace();
			return;
		}
		System.out.println("file length: "+len);
		System.out.println("CRC32: "
			+Long.toHexString(crc.getValue()&0x0ffffffffL));
	}

	///////////////////////////////////////////////////////////////////////
	//////// private parts  ///////////////////////////////////////////////
	///////////////////////////////////////////////////////////////////////

	private static void usage() {
		System.err.println(
			"usage: Tools.CRC32 [-polynomial <hexnum>] [-buildTable]");
	}

	private static int[] buildTable(int crcPolynomial) {
		// adapted from Martin Richardson's Build_CRC_Table

		int x, y, crcValue;
		int[] localCrcTable = new int[256];

		for (x=0; x<=255; x++) {
			crcValue = x;
			for (y=1; y<=8; y++) {
				if ((crcValue & 0x01) == 1) {
					crcValue = (crcValue>>>1) ^ crcPolynomial;
				} else {
					crcValue =  crcValue>>>1;
				}
			}
			localCrcTable[x] = crcValue;
		}
		return localCrcTable;
	}

	private static String hex8(int num) {
		// hex8(): { sprintf(s, "%08x", num); return s; }
		String s = Integer.toHexString(num);
		while (s.length()<8) {
			s="0"+s;
		}
		return s;
	}

	private static void printTable(int polynomial) {
		// Print out Java code to store the table in the .class file
		// as a static int[] array.

		int[] table = buildTable(polynomial);
	
		System.out.println("	static int[] crcTable_"
			+hex8(polynomial)+" = {");
		int numsInRow = 6;
		int x;
		for (x=0; x<=255; x++) {
			if (x%numsInRow == 0) {
				System.out.print("	  ");
			}
			System.out.print("0x"+hex8(table[x]));
			if (x!=255) {
				System.out.print(",");
			}
			if ((x+1)%numsInRow == 0) {
				System.out.println();
			} else {
				System.out.print(" ");
			}
		}
		if ((x%numsInRow) != 0) {
			System.out.println();
		}
		System.out.println("	};");
	}

	// a precomputed table for a popular CRC polynomial
	// generated with: 
	// :.+2,$-1!java Tools.CRC32 -polynomial edb88320 -buildTable

	static int[] crcTable_edb88320 = {
	  0x00000000, 0x77073096, 0xee0e612c, 0x990951ba, 0x076dc419, 0x706af48f,
	  0xe963a535, 0x9e6495a3, 0x0edb8832, 0x79dcb8a4, 0xe0d5e91e, 0x97d2d988,
	  0x09b64c2b, 0x7eb17cbd, 0xe7b82d07, 0x90bf1d91, 0x1db71064, 0x6ab020f2,
	  0xf3b97148, 0x84be41de, 0x1adad47d, 0x6ddde4eb, 0xf4d4b551, 0x83d385c7,
	  0x136c9856, 0x646ba8c0, 0xfd62f97a, 0x8a65c9ec, 0x14015c4f, 0x63066cd9,
	  0xfa0f3d63, 0x8d080df5, 0x3b6e20c8, 0x4c69105e, 0xd56041e4, 0xa2677172,
	  0x3c03e4d1, 0x4b04d447, 0xd20d85fd, 0xa50ab56b, 0x35b5a8fa, 0x42b2986c,
	  0xdbbbc9d6, 0xacbcf940, 0x32d86ce3, 0x45df5c75, 0xdcd60dcf, 0xabd13d59,
	  0x26d930ac, 0x51de003a, 0xc8d75180, 0xbfd06116, 0x21b4f4b5, 0x56b3c423,
	  0xcfba9599, 0xb8bda50f, 0x2802b89e, 0x5f058808, 0xc60cd9b2, 0xb10be924,
	  0x2f6f7c87, 0x58684c11, 0xc1611dab, 0xb6662d3d, 0x76dc4190, 0x01db7106,
	  0x98d220bc, 0xefd5102a, 0x71b18589, 0x06b6b51f, 0x9fbfe4a5, 0xe8b8d433,
	  0x7807c9a2, 0x0f00f934, 0x9609a88e, 0xe10e9818, 0x7f6a0dbb, 0x086d3d2d,
	  0x91646c97, 0xe6635c01, 0x6b6b51f4, 0x1c6c6162, 0x856530d8, 0xf262004e,
	  0x6c0695ed, 0x1b01a57b, 0x8208f4c1, 0xf50fc457, 0x65b0d9c6, 0x12b7e950,
	  0x8bbeb8ea, 0xfcb9887c, 0x62dd1ddf, 0x15da2d49, 0x8cd37cf3, 0xfbd44c65,
	  0x4db26158, 0x3ab551ce, 0xa3bc0074, 0xd4bb30e2, 0x4adfa541, 0x3dd895d7,
	  0xa4d1c46d, 0xd3d6f4fb, 0x4369e96a, 0x346ed9fc, 0xad678846, 0xda60b8d0,
	  0x44042d73, 0x33031de5, 0xaa0a4c5f, 0xdd0d7cc9, 0x5005713c, 0x270241aa,
	  0xbe0b1010, 0xc90c2086, 0x5768b525, 0x206f85b3, 0xb966d409, 0xce61e49f,
	  0x5edef90e, 0x29d9c998, 0xb0d09822, 0xc7d7a8b4, 0x59b33d17, 0x2eb40d81,
	  0xb7bd5c3b, 0xc0ba6cad, 0xedb88320, 0x9abfb3b6, 0x03b6e20c, 0x74b1d29a,
	  0xead54739, 0x9dd277af, 0x04db2615, 0x73dc1683, 0xe3630b12, 0x94643b84,
	  0x0d6d6a3e, 0x7a6a5aa8, 0xe40ecf0b, 0x9309ff9d, 0x0a00ae27, 0x7d079eb1,
	  0xf00f9344, 0x8708a3d2, 0x1e01f268, 0x6906c2fe, 0xf762575d, 0x806567cb,
	  0x196c3671, 0x6e6b06e7, 0xfed41b76, 0x89d32be0, 0x10da7a5a, 0x67dd4acc,
	  0xf9b9df6f, 0x8ebeeff9, 0x17b7be43, 0x60b08ed5, 0xd6d6a3e8, 0xa1d1937e,
	  0x38d8c2c4, 0x4fdff252, 0xd1bb67f1, 0xa6bc5767, 0x3fb506dd, 0x48b2364b,
	  0xd80d2bda, 0xaf0a1b4c, 0x36034af6, 0x41047a60, 0xdf60efc3, 0xa867df55,
	  0x316e8eef, 0x4669be79, 0xcb61b38c, 0xbc66831a, 0x256fd2a0, 0x5268e236,
	  0xcc0c7795, 0xbb0b4703, 0x220216b9, 0x5505262f, 0xc5ba3bbe, 0xb2bd0b28,
	  0x2bb45a92, 0x5cb36a04, 0xc2d7ffa7, 0xb5d0cf31, 0x2cd99e8b, 0x5bdeae1d,
	  0x9b64c2b0, 0xec63f226, 0x756aa39c, 0x026d930a, 0x9c0906a9, 0xeb0e363f,
	  0x72076785, 0x05005713, 0x95bf4a82, 0xe2b87a14, 0x7bb12bae, 0x0cb61b38,
	  0x92d28e9b, 0xe5d5be0d, 0x7cdcefb7, 0x0bdbdf21, 0x86d3d2d4, 0xf1d4e242,
	  0x68ddb3f8, 0x1fda836e, 0x81be16cd, 0xf6b9265b, 0x6fb077e1, 0x18b74777,
	  0x88085ae6, 0xff0f6a70, 0x66063bca, 0x11010b5c, 0x8f659eff, 0xf862ae69,
	  0x616bffd3, 0x166ccf45, 0xa00ae278, 0xd70dd2ee, 0x4e048354, 0x3903b3c2,
	  0xa7672661, 0xd06016f7, 0x4969474d, 0x3e6e77db, 0xaed16a4a, 0xd9d65adc,
	  0x40df0b66, 0x37d83bf0, 0xa9bcae53, 0xdebb9ec5, 0x47b2cf7f, 0x30b5ffe9,
	  0xbdbdf21c, 0xcabac28a, 0x53b39330, 0x24b4a3a6, 0xbad03605, 0xcdd70693,
	  0x54de5729, 0x23d967bf, 0xb3667a2e, 0xc4614ab8, 0x5d681b02, 0x2a6f2b94,
	  0xb40bbe37, 0xc30c8ea1, 0x5a05df1b, 0x2d02ef8d 
	};
}
