[erlang-questions] checksum calculation

Steve Davis <>
Wed Apr 8 13:04:26 CEST 2009


Gamoto,

What I would do is:
1) make a cup of tea,
2) open my browser to http://www.erlang.org/doc/
3)...and start doing some reading.

Steve

On Apr 7, 3:55 am, "Gamoto" <> wrote:
> Richard,
> 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 ;-)
> John
>
>
>
>
>
>
>
> >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
> >that difference.
>
> >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,
> >really.
>
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