85-bits CRC

Dear all:

I have to compute a long CRC (85 bits). I'm used to compute 16-bits and
32-bits CRCs, using tables or using "brute-force" algorithms (via
software) which make use of the fact that 16 bits or 32 bits makes a
word or half a word.

But 85 bits demands, perhpas, other approaches, to be effective. I
wonder if some of you can point me in the right direction. Is there
any other group more suited to be asked? Books, references?

--
Saludos,
Ignacio G.T.

"Ignacio G.T." <> wrote in message
news:...
> Dear all:
>
> I have to compute a long CRC (85 bits).

I am curuous what is this for?

> I'm used to compute 16-bits and
> 32-bits CRCs, using tables or using "brute-force" algorithms (via
> software) which make use of the fact that 16 bits or 32 bits makes a
> word or half a word.
>
> But 85 bits demands, perhpas, other approaches, to be effective.
> I wonder if some of you can point me in the right direction. Is there
> any other group more suited to be asked? Books, references?

CRC is a remainder of the polynomial division. Thus you can extend the 85
bit CRC polynomial to 96 bit polynomial, which is a multiple of machine
word. The 96 bit CRC can be computed efficiently, and then you convert the
96 bit CRC to 85 bits.

Vladimir Vassilevsky
DSP and Mixed Signal Consultant
www.abvolt.com