[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 #39 from Jacob Lifshay <programmerjake at gmail.com> ---
after thinking about a bit, I think gfmul's algorithm can be partially merged
with the gfinv algorithm I posted in comment 33, giving us a gfdiv algorithm
that takes less time than gfinv followed by gfmul.

Let's assume we're calculating gfdiv(N(x), A(x)) (A in the denominator in order
to match the gfinv algorithm).

This is because the U(x) and V(x) polynomials are never used as inputs in the
gfinv algorithm, and the algorithm has some nice additional properties, so we
can change them to clmul(N(x), U(x)) and clmul(N(x), V(x)) throughout the
algorithm, that way the algorithm will return clmul(N(x), gfinv(A(x))) which
will be denoted by T(x). T(x), when reduced by G(x) (the reducing polynomial)
produces the result of gfdiv(N(x), A(x)).

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