MAT key_genmat(gf_t *L, poly_t g)
{
//L- Support
//t- Number of errors, i.e.=30.
//n- Length of the Goppa code, i.e.=2^11
//m- The extension degree of the GF, i.e. =11
//g- The generator polynomial.
gf_t x,y;
MAT H,R;
int i,j,k,r,n;
int * perm, Laux[LENGTH];
n=LENGTH;//2^11=2048
r=NB_ERRORS*gf_extd();//32 x 11=352
H=mat_ini(r,n);//initialize matrix with actual no. of bits.
mat_set_to_zero(H); //set the matrix with all 0's.
for(i=0;i< n;i++)
{
x = poly_eval(g,L[i]);//evaluate the polynomial at the point L[i].
x = gf_inv(x);
y = x;
for(j=0;j<NB_ERRORS;j++)
{
for(k=0;k<gf_extd();k++)
{
if(y & (1<<k))//if((y>>k) & 1)
mat_set_coeff_to_one(H,j*gf_extd()+k,i);//the co-eff. are set in 2^0,...,2^11 ; 2^0,...,2^11 format along the rows/cols?
}
y = gf_mul(y,L[i]);
}
}//The H matrix is fed.
perm = mat_rref(H);
if (perm == NULL) {
mat_free(H);
return NULL;
}
R = mat_ini(n-r,r);
mat_set_to_zero(R); //set the matrix with all 0's.
for (i = 0; i < R->rown; ++i)
for (j = 0; j < R->coln; ++j)
if (mat_coeff(H,j,perm[i]))
mat_change_coeff(R,i,j);
for (i = 0; i < LENGTH; ++i)
Laux[i] = L[perm[i]];
for (i = 0; i < LENGTH; ++i)
L[i] = Laux[i];
mat_free(H);
free(perm);
return (R);
}
// retourne le degré du plus petit facteur
int poly_degppf(poly_t g) {
int i, d, res;
poly_t *u, p, r, s;
d = poly_deg(g);
u = malloc(d * sizeof (poly_t *));
for (i = 0; i < d; ++i)
u[i] = poly_alloc(d + 1);
poly_sqmod_init(g, u);
p = poly_alloc(d - 1);
poly_set_deg(p, 1);
poly_set_coeff(p, 1, gf_unit());
r = poly_alloc(d - 1);
res = d;
for (i = 1; i <= (d / 2) * gf_extd(); ++i) {
poly_sqmod(r, p, u, d);
// r = x^(2^i) mod g
if ((i % gf_extd()) == 0) { // donc 2^i = (2^m)^j (m deg d'extension)
poly_addto_coeff(r, 1, gf_unit());
poly_calcule_deg(r); // le degré peut changer
s = poly_gcd(g, r);
if (poly_deg(s) > 0) {
poly_free(s);
res = i / gf_extd();
break;
}
poly_free(s);
poly_addto_coeff(r, 1, gf_unit());
poly_calcule_deg(r); // le degré peut changer
}
// on se sert de s pour l'échange
s = p;
p = r;
r = s;
}
poly_free(p);
poly_free(r);
for (i = 0; i < d; ++i) {
poly_free(u[i]);
}
free(u);
return res;
}
// Returns the degree of the smallest factor
int poly_degppf(poly_t g) {
int i, d, res;
poly_t *u, p, r, s;
d = poly_deg(g);
u = malloc(d * sizeof (poly_t *));
for (i = 0; i < d; ++i)
u[i] = poly_alloc(d + 1);
poly_sqmod_init(g, u);
p = poly_alloc(d - 1);
poly_set_deg(p, 1);
poly_set_coeff(p, 1, gf_unit());
r = poly_alloc(d - 1);
res = d;
for (i = 1; i <= (d / 2) * gf_extd(); ++i) {
poly_sqmod(r, p, u, d);
// r = x^(2^i) mod g
if ((i % gf_extd()) == 0) { // so 2^i = (2^m)^j (m ext. degree)
poly_addto_coeff(r, 1, gf_unit());
poly_calcule_deg(r); // The degree may change
s = poly_gcd(g, r);
if (poly_deg(s) > 0) {
poly_free(s);
res = i / gf_extd();
break;
}
poly_free(s);
poly_addto_coeff(r, 1, gf_unit());
poly_calcule_deg(r); // The degree may change
}
// No need for the exchange s
s = p;
p = r;
r = s;
}
poly_free(p);
poly_free(r);
for (i = 0; i < d; ++i) {
poly_free(u[i]);
}
free(u);
return res;
}
poly_t * poly_sqrtmod_init(poly_t g) {
int i, t;
poly_t * sqrt, aux, p, q, * sq_aux;
t = poly_deg(g);
sq_aux = malloc(t * sizeof (poly_t));
for (i = 0; i < t; ++i)
sq_aux[i] = poly_alloc(t - 1);
poly_sqmod_init(g, sq_aux);
q = poly_alloc(t - 1);
p = poly_alloc(t - 1);
poly_set_deg(p, 1);
poly_set_coeff(p, 1, gf_unit());
// q(z) = 0, p(z) = z
for (i = 0; i < t * gf_extd() - 1; ++i) {
// q(z) <- p(z)^2 mod g(z)
poly_sqmod(q, p, sq_aux, t);
// q(z) <-> p(z)
aux = q;
q = p;
p = aux;
}
// p(z) = z^(2^(tm-1)) mod g(z) = sqrt(z) mod g(z)
sqrt = malloc(t * sizeof (poly_t));
for (i = 0; i < t; ++i)
sqrt[i] = poly_alloc(t - 1);
poly_set(sqrt[1], p);
poly_calcule_deg(sqrt[1]);
for(i = 3; i < t; i += 2) {
poly_set(sqrt[i], sqrt[i - 2]);
poly_shiftmod(sqrt[i], g);
poly_calcule_deg(sqrt[i]);
}
for (i = 0; i < t; i += 2) {
poly_set_to_zero(sqrt[i]);
sqrt[i]->coeff[i / 2] = gf_unit();
sqrt[i]->deg = i / 2;
}
for (i = 0; i < t; ++i)
poly_free(sq_aux[i]);
free(sq_aux);
poly_free(p);
poly_free(q);
return sqrt;
}
