Package com.github.junrar.crc

Class RarCRC

java.lang.Object

com.github.junrar.crc.RarCRC

public class RarCRC
extends Object

DOCUMENT ME

Method Summary

Modifier and Type	Method	Description
static short	checkOldCrc(short startCrc, byte[] data, int count)	Computes the legacy 16-bit checksum used by RAR 1.5 archives.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Method Details

checkOldCrc

public static short checkOldCrc(short startCrc,
 byte[] data,
 int count)

Computes the legacy 16-bit checksum used by RAR 1.5 archives.

This is not a standard CRC-16 algorithm. It is a simple rotating-add checksum equivalent to the OldCRC16 function in the original unrar source code. For each byte, it adds the byte value to the accumulator and then rotates the result left by 1 bit:

   crc = crc + byte;
   crc = (crc << 1) | (crc >>> 15);
 

Only used for RAR 1.5 (method 15) archives. RAR 2.0 and later use standard CRC-32 (polynomial 0xEDB88320).

Parameters:

startCrc - initial CRC value (typically 0 for RAR 1.5)

data - data to compute the checksum over

count - number of bytes to process

Returns:

the 16-bit rotating-add checksum