Mein JavaCode rechnet die Prüfsumme CRC-CCITT der eingegebenen Zeichen. Allerdings geht das nur bei einer geraden Anzahl Zeichen richtig. Hat jemand ne Ahnung wieso das bei ungerader Anzahl nicht geht? Ich komme einfach auf keinen grünen Zweig... JavaCode
1 | public class Crc_CCITT //xModem |
2 | { |
3 | |
4 | long act_CRC_ul; |
5 | |
6 | // String [] test = new String[] {"E0", "06", "52"}; //--> Soll CRC = 7020 / ist= 5e97 XX |
7 | String[] test = new String[] {"E0", "06", "52", "53"}; //--> Soll CRC = 3401 / ist= 3401 OK |
8 | // String [] test = new String[] {"E0", "06", "52", "53", "44"}; //--> Soll CRC = 7F97 / ist= 1878 XX |
9 | // String [] test = new String[] {"E0", "06", "52", "53", "44", "E7"}; //--> Soll CRC = 95B1 / ist= 95B1 OK |
10 | |
11 | public Crc_CCITT() |
12 | { |
13 | calcCRC(makeIntArray()); |
14 | System.out.println(Long.toHexString(act_CRC_ul & 0xFFFF)); |
15 | } |
16 | public static void main(String[] args) |
17 | { |
18 | Crc_CCITT crc= new Crc_CCITT(); |
19 | } |
20 | |
21 | private int[] makeIntArray()//rechnet die Strings in Int-werte um. |
22 | { |
23 | int[] zeichen = new int[test.length]; |
24 | for (int n = 0; n < test.length; n++) |
25 | { |
26 | zeichen[n] = Integer.parseInt(test[n], 16); |
27 | } |
28 | return zeichen; |
29 | } |
30 | |
31 | private void calcCRC(int[] msg) |
32 | { |
33 | int u; |
34 | int msb_c, lsb_c; |
35 | // |
36 | act_CRC_ul = 0L; |
37 | // erste 2 Bytes MSB und LSB invertiert: |
38 | msb_c = msg[0]; |
39 | lsb_c = msg[1]; |
40 | |
41 | msg_upd2crc(msb_c, lsb_c); |
42 | // rest der MSG: |
43 | for (u = 2; u < msg.length; u++) |
44 | { |
45 | lsb_c = msg[u]; |
46 | u++; |
47 | if (u == msg.length) |
48 | { |
49 | msb_c = 0; // when message length is odd |
50 | } |
51 | else |
52 | { |
53 | msb_c = msg[u]; |
54 | } |
55 | msg_upd2crc(lsb_c, msb_c); |
56 | } |
57 | msg_upd2crc(0, 0); |
58 | } |
59 | public void msg_upd2crc(int msb_c, int lsb_c) |
60 | { |
61 | long shifter_w, data_w; |
62 | long carry_w; |
63 | |
64 | shifter_w = 0x8000L; |
65 | data_w = (((msb_c << 8) & 0xff00L) | (lsb_c & 0x00ffL)); |
66 | |
67 | do |
68 | { |
69 | carry_w = act_CRC_ul & 0x8000L; |
70 | |
71 | act_CRC_ul <<= 1; |
72 | |
73 | if ((data_w & shifter_w) != 0L) |
74 | { |
75 | act_CRC_ul++; |
76 | } |
77 | if (carry_w != 0L) |
78 | { |
79 | act_CRC_ul ^= 0x1021L; |
80 | } |
81 | shifter_w >>= 1; |
82 | act_CRC_ul &= 0xFFFFFF; |
83 | } |
84 | while (shifter_w != 0L); |
85 | } |
86 | } |