com.datastax.oss.protocol.internal.util

Class Crc

java.lang.Object

com.datastax.oss.protocol.internal.util.Crc

public class Crc
extends Object

Copied and adapted from the server-side version.

Constructor Summary

Constructors

Constructor and Description
Crc()

Method Summary

Modifier and Type	Method and Description
static int	computeCrc24(long bytes, int len) NOTE: the order of bytes must reach the wire in the same order the CRC is computed, with the CRC immediately following in a trailer.
static <B> int	computeCrc32(B buffer, PrimitiveCodec<B> codec)

Methods inherited from class java.lang.Object

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

Constructor Detail

Crc

public Crc()

Method Detail

computeCrc32

public static <B> int computeCrc32(B buffer,
                                   PrimitiveCodec<B> codec)

computeCrc24

public static int computeCrc24(long bytes,
                               int len)

NOTE: the order of bytes must reach the wire in the same order the CRC is computed, with the CRC immediately following in a trailer. Since we read in least significant byte order, if you write to a buffer using putInt or putLong, the byte order will be reversed and you will lose the guarantee of protection from burst corruptions of 24 bits in length.

Make sure either to write byte-by-byte to the wire, or to use Integer/Long.reverseBytes if you write to a BIG_ENDIAN buffer.

See http://users.ece.cmu.edu/~koopman/pubs/ray06_crcalgorithms.pdf

Complain to the ethernet spec writers, for having inverse bit to byte significance order.

Note we use the most naive algorithm here. We support at most 8 bytes, and typically supply 5 or fewer, so any efficiency of a table approach is swallowed by the time to hit L3, even for a tiny (4bit) table.

Parameters:

bytes - an up to 8-byte register containing bytes to compute the CRC over the bytes AND bits will be read least-significant to most significant.

len - the number of bytes, greater than 0 and fewer than 9, to be read from bytes

Returns:

the least-significant bit AND byte order crc24 using the CRC24_POLY polynomial