Main.java Source code

Introduction

Here is the source code for Main.java

Source

//package com.java2s;
//License from project: Apache License 

import org.apache.commons.codec.binary.Hex;
import java.util.Arrays;

public class Main {
    public static void testChecksum(String inputString, String expectedSum) throws Exception {
        byte[] sample = Hex.decodeHex(inputString.toCharArray());
        byte[] sampleCheckSum = Hex.decodeHex(expectedSum.toCharArray());
        char checksum = checkSum(sample);
        byte[] result = { (byte) (checksum & 0xFF), (byte) ((checksum >> 8) & 0xFF) };
        System.out.println("Calculated checksum: " + byteArrayToString(result) + " vs expected: " + expectedSum);

        // Confirmation
        char checksumComp = (char) (checksum ^ 0xFFFF);
        byte verifySample[] = Arrays.copyOf(sample, sample.length + 2);
        verifySample[verifySample.length - 4] = (byte) (checksumComp & 0xFF);
        verifySample[verifySample.length - 3] = (byte) (checksumComp >> 8);
        char verifier = checkSum(verifySample);
        byte[] verifierResult = { (byte) (verifier & 0xFF), (byte) ((verifier >> 8) & 0xFF) };
        System.out.println("Verifier = " + byteArrayToString(verifierResult));
    }

    /**
     * Calculates the checksum of a given command package.
     * It assumes the provided buffer has space for the checksum at the end (2 bytes) so those
     * two bytes are not included in the checksum calculation
     *
     * See Appendix A of "clearpath control protocol" doc,to understand how to implement it
     * - Polynomial: x16+x12+x5+1 (0x1021)
     * - Initial value: 0xFFFF
     * - Check constant: 0x1D0F
     */
    public static char checkSum(byte[] cmdPackage) {
        //CRC lookup table for polynomial 0x1021
        char table[] = { 0x0, 0x1021, 0x2042, 0x3063, 0x4084, 0x50a5, 0x60c6, 0x70e7, 0x8108, 0x9129, 0xa14a,
                0xb16b, 0xc18c, 0xd1ad, 0xe1ce, 0xf1ef, 0x1231, 0x210, 0x3273, 0x2252, 0x52b5, 0x4294, 0x72f7,
                0x62d6, 0x9339, 0x8318, 0xb37b, 0xa35a, 0xd3bd, 0xc39c, 0xf3ff, 0xe3de, 0x2462, 0x3443, 0x420,
                0x1401, 0x64e6, 0x74c7, 0x44a4, 0x5485, 0xa56a, 0xb54b, 0x8528, 0x9509, 0xe5ee, 0xf5cf, 0xc5ac,
                0xd58d, 0x3653, 0x2672, 0x1611, 0x630, 0x76d7, 0x66f6, 0x5695, 0x46b4, 0xb75b, 0xa77a, 0x9719,
                0x8738, 0xf7df, 0xe7fe, 0xd79d, 0xc7bc, 0x48c4, 0x58e5, 0x6886, 0x78a7, 0x840, 0x1861, 0x2802,
                0x3823, 0xc9cc, 0xd9ed, 0xe98e, 0xf9af, 0x8948, 0x9969, 0xa90a, 0xb92b, 0x5af5, 0x4ad4, 0x7ab7,
                0x6a96, 0x1a71, 0xa50, 0x3a33, 0x2a12, 0xdbfd, 0xcbdc, 0xfbbf, 0xeb9e, 0x9b79, 0x8b58, 0xbb3b,
                0xab1a, 0x6ca6, 0x7c87, 0x4ce4, 0x5cc5, 0x2c22, 0x3c03, 0xc60, 0x1c41, 0xedae, 0xfd8f, 0xcdec,
                0xddcd, 0xad2a, 0xbd0b, 0x8d68, 0x9d49, 0x7e97, 0x6eb6, 0x5ed5, 0x4ef4, 0x3e13, 0x2e32, 0x1e51,
                0xe70, 0xff9f, 0xefbe, 0xdfdd, 0xcffc, 0xbf1b, 0xaf3a, 0x9f59, 0x8f78, 0x9188, 0x81a9, 0xb1ca,
                0xa1eb, 0xd10c, 0xc12d, 0xf14e, 0xe16f, 0x1080, 0xa1, 0x30c2, 0x20e3, 0x5004, 0x4025, 0x7046,
                0x6067, 0x83b9, 0x9398, 0xa3fb, 0xb3da, 0xc33d, 0xd31c, 0xe37f, 0xf35e, 0x2b1, 0x1290, 0x22f3,
                0x32d2, 0x4235, 0x5214, 0x6277, 0x7256, 0xb5ea, 0xa5cb, 0x95a8, 0x8589, 0xf56e, 0xe54f, 0xd52c,
                0xc50d, 0x34e2, 0x24c3, 0x14a0, 0x481, 0x7466, 0x6447, 0x5424, 0x4405, 0xa7db, 0xb7fa, 0x8799,
                0x97b8, 0xe75f, 0xf77e, 0xc71d, 0xd73c, 0x26d3, 0x36f2, 0x691, 0x16b0, 0x6657, 0x7676, 0x4615,
                0x5634, 0xd94c, 0xc96d, 0xf90e, 0xe92f, 0x99c8, 0x89e9, 0xb98a, 0xa9ab, 0x5844, 0x4865, 0x7806,
                0x6827, 0x18c0, 0x8e1, 0x3882, 0x28a3, 0xcb7d, 0xdb5c, 0xeb3f, 0xfb1e, 0x8bf9, 0x9bd8, 0xabbb,
                0xbb9a, 0x4a75, 0x5a54, 0x6a37, 0x7a16, 0xaf1, 0x1ad0, 0x2ab3, 0x3a92, 0xfd2e, 0xed0f, 0xdd6c,
                0xcd4d, 0xbdaa, 0xad8b, 0x9de8, 0x8dc9, 0x7c26, 0x6c07, 0x5c64, 0x4c45, 0x3ca2, 0x2c83, 0x1ce0,
                0xcc1, 0xef1f, 0xff3e, 0xcf5d, 0xdf7c, 0xaf9b, 0xbfba, 0x8fd9, 0x9ff8, 0x6e17, 0x7e36, 0x4e55,
                0x5e74, 0x2e93, 0x3eb2, 0xed1, 0x1ef0 };

        int size = cmdPackage.length - 2;
        char checksum = 0xFFFF;
        int counter = 0;
        while (counter < size) {
            checksum = (char) ((char) (checksum << 8) ^ table[((checksum >> 8) ^ cmdPackage[counter]) & 0xFF]);
            counter++;
        }
        return checksum;
    }

    public static String byteArrayToString(byte[] data) {
        return new String(Hex.encodeHex(data));
    }
}