[Libre-soc-bugs] [Bug 782] add galois field bitmanip instructions

[bugzilla-daemon at libre-soc.org]

https://bugs.libre-soc.org/show_bug.cgi?id=782

--- Comment #13 from Jacob Lifshay <programmerjake at gmail.com> ---
(In reply to Luke Kenneth Casson Leighton from comment #11)
> correct me if wrong i believe it quite simple to show XOR insufficient
> 
> polynomial 0b110001
> x          0b110000
> y          0b001111
> XOR        0b111111
> clearly this is greater than the polynomial which modulo you are
> supposed to XOR and instead get the correct answer:

well, that's because you started with something bigger you should
have...remember, these are polynomials, so any bit set means you divide it out.

> polynomial 0b110001
> x          0b110000

here x would have to be reduced to something without the top bit set, only
after reducing it is it a value you'd actually expect to have as an input. I'm
not working out what it'd reduce to at the moment, it's 4:30am here.

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