void gf2m_decomp_rootfind_state::calc_next_Aij()
{
/*
* upon function entry, we have in the state j, Aij.
* first thing, we declare Aij Aij_minusone and increase j.
* Case j=0 upon function entry also included, then Aij contains A_{i,j=0}.
*/
uint32_t i;
gf2m diff, new_j_gray;
uint32_t Lik_pos_base;
this->m_j++;
new_j_gray = lex_to_gray(this->m_j);
if(this->m_j & 1) /* half of the times */
{
Lik_pos_base = 0;
}
else if(this->m_j & 2) /* one quarter of the times */
{
Lik_pos_base = this->m_outer_summands;
}
else if( this->m_j & 4) /* one eighth of the times */
{
Lik_pos_base = this->m_outer_summands * 2;
}
else if( this->m_j & 8) /* one sixteenth of the times */
{
Lik_pos_base = this->m_outer_summands * 3;
}
else if( this->m_j & 16) /* ... */
{
Lik_pos_base = this->m_outer_summands * 4;
}
else
{
gf2m delta_offs = 5;
diff = this->m_j_gray ^ new_j_gray;
while(((static_cast<gf2m>(1) << delta_offs) & diff) == 0)
{
delta_offs++;
}
Lik_pos_base = delta_offs * this->m_outer_summands;
}
this->m_j_gray = new_j_gray;
i = 0;
for(; i < this->m_outer_summands; i++)
{
this->m_Aij[i] ^= this->m_Lik[Lik_pos_base + i];
}
}
std::unique_ptr<binary_matrix> generate_R(std::vector<gf2m> &L, polyn_gf2m* g, std::shared_ptr<GF2m_Field> sp_field, u32bit code_length, u32bit t )
{
//L- Support
//t- Number of errors
//n- Length of the Goppa code
//m- The extension degree of the GF
//g- The generator polynomial.
gf2m x,y;
u32bit i,j,k,r,n;
std::vector<int> Laux(code_length);
n=code_length;
r=t*sp_field->get_extension_degree();
binary_matrix H(r, n) ;
for(i=0; i< n; i++)
{
x = g->eval(lex_to_gray(L[i]));//evaluate the polynomial at the point L[i].
x = sp_field->gf_inv(x);
y = x;
for(j=0; j<t; j++)
{
for(k=0; k<sp_field->get_extension_degree(); k++)
{
if(y & (1<<k))
{
//the co-eff. are set in 2^0,...,2^11 ; 2^0,...,2^11 format along the rows/cols?
H.set_coef_to_one(j*sp_field->get_extension_degree()+ k,i);
}
}
y = sp_field->gf_mul(y,lex_to_gray(L[i]));
}
}//The H matrix is fed.
secure_vector<int> perm = H.row_reduced_echelon_form();
if (perm.size() == 0)
{
// result still is NULL
throw Invalid_State("could not bring matrix in row reduced echelon form");
}
std::unique_ptr<binary_matrix> result(new binary_matrix(n-r,r)) ;
for (i = 0; i < (*result).m_rown; ++i)
{
for (j = 0; j < (*result).m_coln; ++j)
{
if (H.coef(j,perm[i]))
{
result->toggle_coeff(i,j);
}
}
}
for (i = 0; i < code_length; ++i)
{
Laux[i] = L[perm[i]];
}
for (i = 0; i < code_length; ++i)
{
L[i] = Laux[i];
}
return result;
}
