in reply to How to use perl digest module to calculate CRC?

That CRC implementation is broken. It is not manipulating bits; but rather bytes of 1s and 0s. Digest::CRC will never match its output.

It could be that the conflation of bits and bytes is deliberate for sound reasoning; but if I had to guess (which I do as I cannot locate further info on the code), it is simply that the author didn't understand the difference.

Why have you selected that particular CRC algorithm/implementation as you model? If it is simply the first result you found; choose more wisely.

It isn't hard to match its output; but you would be better off using a proper CRC.

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  • Comment on Re: How to use perl digest module to calculate CRC?

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Re^2: How to use perl digest module to calculate CRC?
by guyra (Novice) on Mar 21, 2013 at 11:22 UTC

    I understand.

    Can you recomend a proper crc calculator?

    Thx
[reply]
      Can you recomend a proper crc calculator?

      Do you mean code, or an on-line calculator?

      Either way, the first thing to know is: why are you calculating a crc? What are you hoping it will do for you?

      With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'
      Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
      "Science is about questioning the status quo. Questioning authority".
      In the absence of evidence, opinion is indistinguishable from prejudice.
[reply]

        First, thx for your support!

        The reason I need it:

        I'm acting as a transmitter, and I need to calculate the CRC and then send it along with the message.

        The CRC algorithem that I'm using is not standard.

        P = 1EDC6F41

        Init value = FFFFFFFF

        The file that I'm working on is generated by an in-house script that we have.

        The address should not be part of the CRC calc. Only the HEX bytes.

        All the lines in the file should be considered as one message.

        So what should I do prior to send the data into the digest::CRC?

        Thx again :)

        Guy

[reply]

        I have a file containing data in HEX.

        example:

        @0000 FF FF FF 02 24 E0 02 26 A9 02 21 B0 02 21 53 02

        @0010 21 6A 02 21 EE 02 21 F5 02 25 55 02 22 7B 02 23

        @0090 D2 AF D2 B8 75 1F 01 12 0B B1 75 15 00 E5 0B 20

        etc..

        I need to calculate the CRC for this data:

        my poly is non-standard.

        P=1edc6f41

        init value = 0xFFFFFFFF

        I'm going to use the digect::CRC to do it and I want some kind of a model as a reference to know that I do it correctly.

        By the way, as far as I understand, the digest::CRC consider the data as an ASCII string.

        Meaning it takes each char, gets it ascii value, and then convert it to BIN.

        This is not what I need.

        Ineed it to take the chars and consider them as a HEX value, and just convert them to BIN.

        Any idea on how I should achive it?

        Thx a lot

        Guy.

[reply]

        Still working on getting al the params.

        However, it seems that there is a problem with this approach.

        Not all HEX values have a "valid" ascii value that can be sent to the digest::crc.

        For example: if HEX=01 --> ASCII=SOH, which is not really a char that can be sent.

        That means that many HEX vals can't be in the game...

        Am I correct about that?

        If so, is there any other Perl olution for CRC on HEX data?

        Thx

[reply]

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