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simplified check matrix creation

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This commit is contained in:
Mirek Kratochvil 2012-05-15 13:58:48 +02:00
parent 2f8dfb56af
commit 0db682e5df
1 changed files with 10 additions and 29 deletions
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39
lib/polynomial.cpp
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@ -222,37 +222,18 @@ uint polynomial::eval (uint x, gf2m&fld) const
void polynomial::compute_goppa_check_matrix (matrix&r, gf2m&fld) void polynomial::compute_goppa_check_matrix (matrix&r, gf2m&fld)
{ {
if (degree() < 0) return; //wrongly initialized polynomial if (degree() < 0) return; //wrongly initialized polynomial
uint t = degree();
vector<polynomial> vd, h; //matrix over fld
uint i, j, k;
//construction from Barreto's slides with maximal support L=[0..fld.n)
vd.resize (fld.n);
for (i = 0; i < fld.n; ++i) {
vd[i].resize (t);
vd[i][0] = fld.inv (eval (i, fld) );
}
//compute support powers
for (j = 0; j < fld.n; ++j) for (i = 1; i < t; ++i)
vd[j][i] = fld.mult (vd[j][i-1], j);
//multiply by goppa coefficients (compute t*vd)
h.resize (fld.n);
for (i = 0; i < fld.n; ++i) {
h[i].resize (t);
for (j = 0; j < t; ++j) { //computing the element h[i][j]
h[i][j] = 0;
for (k = 0; k <= j; ++k) //k = column index of t
h[i][j] = fld.add (h[i][j],
fld.mult (item (t + k - j),
vd[i][k]) );
}
}
//now convert to binary
r.resize (fld.n); r.resize (fld.n);
for (i = 0; i < fld.n; ++i)
r[i].from_poly (h[i], fld); for (uint i = 0; i < fld.n; ++i) {
polynomial col;
col.resize (2);
col[0] = i;
col[1] = 1;
col.inv(*this,fld);
//i-th row of the check matrix is polynomial 1/(x-i)
r[i].from_poly(col,fld);
}
} }
void polynomial::make_monic (gf2m&fld) void polynomial::make_monic (gf2m&fld)