CRC16校验码的JAVA实现

http://hi.baidu.com/fanthes/blog/item/f684e5cdc061f3510eb34503.html

1．Design   2．Codeimport java.io.IOException; public class CRC16Checker {             private static int[] index = new int[] { 16, 15, 2, 0 };             private static int[] getBinary(String text) {                        StringBuffer num = new StringBuffer();                        String s; char ch;                        for (int i = 0; i < text.length(); i++) { // Change each char to binary code.                                    s = Integer.toBinaryString(text.charAt(i));                                    // If the code is less than 8 bit, make it as 8 bit.                                    for (int j = 8 - s.length(); j > 0; j--) num.append(0);                                    num.append(s);                        }                        int len = num.length();                        int[] code = new int[len];                        for (int i = 0; i < len; i++) // Change each 0/1 char to int.                            code[i] = Character.getNumericValue(num.charAt(i));                        return code;            }             private static String toHex(int[] num) {                        StringBuffer hex = new StringBuffer(num.length / 4);                        char[] ch = new char[4];                        for (int i = 0; i < num.length;) {                            // Change each 0/1 int to char.                                    ch[0] = Character.forDigit(num[i++], 2);                                    ch[1] = Character.forDigit(num[i++], 2);                                    ch[2] = Character.forDigit(num[i++], 2);                                    ch[3] = Character.forDigit(num[i++], 2);                                    // Change each 4-bit-code to hex number.                                    hex.append(Integer.toHexString(Integer.parseInt(String.valueOf(ch), 2)));                        }                        return hex.toString();            } // CRC codes main process            public static int[] makeCRCCodes(int[] sourceCodes, int[] multinomial) {                        // The lenght of CRC code is N bits longer than source code. The codes                         // from 0 to sourceLength are same as the source. N bits after source                         // are the CRC codes. N is decided by the multinomial.                        // CRC码数组总长为原码长加上校验码码长。数组前部存放原码。校验码存放在数组                        // 最后的N位。校验码长度决定于生成多项式数组0位置上的元素。                        int sourceLength = sourceCodes.length;                        int codesLength = sourceLength + multinomial[0];                        int[] crcCodes = new int[codesLength];                        // Copy source code from 0 to sourceLength. 拷贝原码。                        System.arraycopy(sourceCodes, 0, crcCodes, 0, sourceLength);                        int temp, pos;                        // Division system. 除法器。                        for (int i = 0; i < sourceLength; i++) {                                    // Count value of the input adding the first register.                                    // 用第i位原码和第一个寄存器值模二加。                                    temp = (crcCodes[sourceLength] + sourceCodes[i]) % 2;                                     // Move registers forwards from (1, length) to (0, length - 1).                                     // 第二个寄存器及以后的所有寄存器值前移1位。                                    System.arraycopy(                                                crcCodes, sourceLength + 1, crcCodes, sourceLength, multinomial[0] - 1);                                    // Set the last register with counted value.                                     // 最后一个寄存器值存放计算好的输入值。                                    crcCodes[codesLength - 1] = temp;                                    // Count other registers. 按生成多项式的值算出位置，模二加出该寄存器的值。                                    for (int j = index.length - 2; j > 0; j--) {                                                pos = codesLength - multinomial[j] - 1;                                                crcCodes[pos] = (crcCodes[pos] + temp) % 2;                                    }                        }                        return crcCodes;            }             public static void main(String[] args) throws IOException {                        System.out.print("Input hex data :");                        StringBuffer buf = new StringBuffer();                        char ch = (char) System.in.read();                        while (ch != '\r' && ch != '\n') {                                    buf.append(ch);                                    ch = (char) System.in.read();                        }                        // Get binary codes.                        int[] b = CRC16Checker.getBinary(buf.toString());                        // Make CRC codes.                        b = CRC16Checker.makeCRCCodes(b, CRC16Checker.index);                         // Output code as binary number.                         for (int i = 0; i < b.length;) {                                    for (int j = 0; j < 4; j++, i++) System.out.print(b[i]);                                    System.out.print(' ');                        }                        System.out.println();                        // Output code as hex number.                         System.out.println("The CRC16 code is :" + CRC16Checker.toHex(b));            }} 3. Test report :Case : A （ASCII = 41）Result : 410186CRC bits : 0168 （0000 0001 1000 0110）Run program :Input hex data :A0100 0001 0000 0001 1000 0110The CRC16 code is :410186 Case : CRC16TEST （ASCII = 43 52 43 31 36 54 45 53 54）Result : 455243313654455354fb66 CRC bits : fb66 （1111 1011 0110 0110）Run program :Input hex data :CRC16TEST0100 0011 0101 0010 0100 0011 0011 0001 0011 0110 0101 0100 0100 0101 0101 0011 0101 0100 1111 1011 0110 0110The CRC16 code is :435243313654455354fb66 Case : 5k （ASCII = 35 6b）Result : 356b3f79 CRC bits : 3f79 （0011 1111 0111 1001）Run program :Input hex data :5k0011 0101 0110 1011 0011 1111 0111 1001The CRC16 code is :356b3f79