[avr-libc-dev] [bug #37901] CRC-CCITT calculation incorrect

[Joerg Wunsch]

Update of bug #37901 (project avr-libc):

             Open/Closed:                  Closed => Open                   

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Follow-up Comment #3:

> The standard CCITT CRC should produce an endian
> and bit-order independent result that is compatible
> with other implementations.

It's simply impossible to implement a bit-order independent CRC.  The
existing _crc_ccitt_update() is known to work with any kind of
communication protocol that transfers the low-order bit first (not
only IrDA but many others; probably any communication protocol except
USB works this way).

If anyone wants the opposite-bit-order CRC function that is compatible
with the Xmega CRC, they ought to use _crc_xmodem_update().

Yes, renaming anything is sheer impossible, as it would break
backwards compatibility for all those people who use the current
functions.

I reopen the bug report so you can append a patch that you think would
make the documentation clearer on this.  Perhaps mention that
_crc_xmodem_update() is the one that is compatible with the Xmega CRC?
Insert a paragraph describing the bit-order problem?


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