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000090_news@newsmaster….columbia.edu _Sun May 17 19:13:28 1998.msg
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From: fdc@watsun.cc.columbia.edu (Frank da Cruz)
Newsgroups: comp.protocols.kermit.misc
Subject: Re: CRC-CCITT in C-Kermit?
Date: 17 May 1998 23:13:25 GMT
Organization: Columbia University
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In article <355f6176.22879615@149.174.211.108>,
Ron Heiby <heiby_u@falkor.chi.il.us> wrote:
: Hi! I'm trying to come up with definition and example implementation of
: CRC-CCITT for a standards effort I'm involved with.
:
: I have run across several implementations that claim to implement CRC-CCITT.
:
I think they are probably all compatible in the sense that they use the same
generating polynomial, i.e. the one prescribed by the CCITT (ITU-T) for the
16-bit CRC. The fact that they arrive at different results most likely
indicates different starting conditions, like:
: ... the CRC must be pre-loaded with 0xffff ...
Kermit's is initialized to 0.
Hint: When implementing CRC calculation in C, be sure to use unsigned
arithmetic, and to avoid implicit conversion of arithmetic operands to signed.
- Frank