byte sorting

[lascar]

I'm trying to write some java code in order to talk to a RFID device.
The protocol I must follow (ISO don't recall what number) asks for every
query to end with a CRC.
This CRC must be expressed in a 'least significant byte first' and,
within a byte, 'least significant bit first'.
I can decide the order of my 2 CRC bytes. Shall I also work on bitwise
operations in order to set all bits properly, or is this something
implicit within the java architecture?
Thanks,
Las

 

[John C. Bollinger]

I'm trying to write some java code in order to talk to a RFID device.
The protocol I must follow (ISO don't recall what number) asks for every
query to end with a CRC.
This CRC must be expressed in a 'least significant byte first' and,
within a byte, 'least significant bit first'.
I can decide the order of my 2 CRC bytes. Shall I also work on bitwise
operations in order to set all bits properly, or is this something
implicit within the java architecture?

Java integer types are logically big-endian with respect to byte order,
and logically big-endian with respect to bit order within any byte.
(How these things are expressed in the underlying hardware is
irrelevant.) Java I/O and networking API will not perform bit
reordering for you.


John Bollinger
(e-mail address removed)

 

[Roedy Green]

I can decide the order of my 2 CRC bytes. Shall I also work on bitwise
operations in order to set all bits properly, or is this something
implicit within the java architecture?

Java does all i/o bigendian. If you want it little endian you must
take special measures.

See http://mindprod.com/jgloss/endian.html