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custom CRC

Posted: 30 Apr 2012 22:47
by poposhka
Hello. I'm trying to calculate a custom CRC on a file. The instructions aren't very clear, would it be possible to add how to do this in a manual or something?

I'm trying to use the polynomial: x^24 + 4x^3 + 3x + 1

Thanks for any help.

Re: custom CRC

Posted: 03 May 2012 01:45
by Maƫl
Have a look at wikipedia http://en.wikipedia.org/wiki/Cyclic_redundancy_check especially the sections "Specification of CRC" and "Commonly used and standardized CRCs". They tell you how you can determine the params for the Custom CRC in HxD.

For example, for CRC-32 the values are: polynomial = 0x04C11DB7, InitialValue = 0xFFFFFFFF, FinalXorValue = 0xFFFFFFFF, ReflectIn = True, ReflectOut = True. In case you only know the polynomial try playing with ReflectIn, ReflectOut (can be true or false) and InitialValue and FinalXorValue (most likely either 0xFFFFFFFF or 0x00000000).

See also here: http://regregex.bbcmicro.net/crc-catalogue.htm