crc32.java

提供JAVA平台的CRC解密程序

/*************************************************************************
 *  Compilation:  javac CRC32.java CharStdIn.java
 *  Execution:    java CRC32 < data.txt
 *  
 *  Reads in a sequence of bytes and prints out their 32 bit
 *  Cylcic Redundancy Check (CRC32 or Ethernet / AAL5 or ITU-TSS).
 *
 *  0 1 2 4 5 7 8 10 11 12 16 22 23 26 32
 *
 *************************************************************************/

public class CRC32 { 

   public static void main(String[] args) { 
      int crc = 0xFFFFFFFF;       // initial contents of LFBSR

      while (!CharStdIn.isEmpty()) {
         char c = CharStdIn.readChar();
         // read 8 bits one at a time
         for (int i = 0; i < 8; i++) {
            boolean c31 = ((crc >>> 31      & 1) == 1);
            boolean bit = ((c   >>> (7 - i) & 1) == 1);
            crc <<= 1;
        
           /**************************************************************
            * Uses irreducible polynomial:
            *    1    + x    + x^2  + x^4  + x^5  + x^7  + x^8  +
            *    x^10 + x^11 + x^12 + x^16 + x^22 + x^23 + x^26 
            *
            * 0000 0100 1100 0001 0001 1101 1011 0111                 
            *    0    4    C    1    1    D    B    7
            **************************************************************/
            if (c31 ^ bit) crc ^= 0x04C11DB7;
         }
      }
      System.out.println("CRC32 = " + crc);
      System.out.println("CRC32 = " + Integer.toHexString(crc));
   }

}