[erlang-questions] checksum calculation
Tue Apr 7 10:55:53 CEST 2009
Suppose you have an industrial machine which send messages following by the checksum calculated by the xor of all bytes, what can I do with your advices ;-)
>On 6 Apr 2009, at 9:34 pm, Gamoto wrote:
>> If it is not a very good solution, would you like to suggest a
>> better one, for me and the other readers ?\
>Suppose you have a block of bytes and there is an
>error that results in one byte being replaced by
>a different byte. Then an XOR checksum will detect
>Suppose there is an error that results in two bytes
>being swapped. Then an XOR checksum will detect no
>change at all. Or suppose that two equal bytes are
>both replaced by the same new byte. Again, nothing
>noticed by XOR.
>Just look "checksum" up in the Wikipedia; that's as
>good a place as any to start.
>The 'zlib' module in Erlang already has support for
>crc32 and adler32. I thought I saw crc32 somewhere
>else as well.
>Theory and practice don't agree as much in practice
>as they do in theory, so it's worth having a look at
>"Performance of Checksums and CRCs over Real Data"
>by Jonathan Stone, Michael Greenwald, Craig Partridge,
>and Jim Hughes
>and at "Revisiting Fletcher and Adler Checksums"
>by Theresa Maxino, whose conclusions I found surprising.
>It all depends on what your data are like and what
>kinds of errors you plausibly need to protect against,
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