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experimenting with 3 times faster EEA

Browse source 
https://en.wikipedia.org/wiki/Extended_Euclidean_algorithm#Simple_algebraic_field_extensions
This commit is contained in:
Ahmet Inan 2023-04-21 08:17:11 +02:00
commit 9570346a59
1 changed files with 22 additions and 0 deletions
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22
galois_field.hh
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@ -392,10 +392,32 @@ template <int M, int64_t POLY, typename TYPE>
GaloisFieldReference<M, POLY, TYPE> rcp(GaloisFieldReference<M, POLY, TYPE> a)
{
assert(a.v);
#if 1
uint32_t r = POLY, newr = a.v;
uint32_t t = 0, newt = 1;
auto degree = [](uint32_t a) {
int d = 0;
while (a >>= 1)
++d;
return d;
};
while (newr != 1) {
int j = degree(newr) - degree(r);
if (j < 0) {
j = -j;
std::swap(newr, r);
std::swap(newt, t);
}
newr ^= r << j;
newt ^= t << j;
}
return GaloisFieldReference<M, POLY, TYPE>(newt);
#else
GaloisFieldReference<M, POLY, TYPE> t(a *= a);
for (int i = 0; i < M - 2; ++i)
t *= a *= a;
return t;
#endif
}
template <int M, int64_t POLY, typename TYPE>