static int fq_sign(element_ptr n) {
int res;
eptr r = n->data;
res = element_sign(r->x);
if (!res) return element_sign(r->y);
return res;
}
// Requires e to be a point on an elliptic curve.
int element_from_bytes_compressed(element_ptr e, unsigned char *data) {
curve_data_ptr cdp = (curve_data_ptr)e->field->data;
point_ptr P = (point_ptr)e->data;
int len;
len = element_from_bytes(P->x, data);
point_from_x(P, P->x, cdp->a, cdp->b);
if (data[len]) {
if (element_sign(P->y) < 0) element_neg(P->y, P->y);
} else if (element_sign(P->y) > 0) {
element_neg(P->y, P->y);
}
len++;
return len;
}
// Requires e to be a point on an elliptic curve.
int element_to_bytes_compressed(unsigned char *data, element_ptr e) {
point_ptr P = (point_ptr)e->data;
int len;
len = element_to_bytes(data, P->x);
if (element_sign(P->y) > 0) {
data[len] = 1;
} else {
data[len] = 0;
}
len++;
return len;
}
static int curve_sign(element_ptr e) {
point_ptr p = (point_ptr)e->data;
if (p->inf_flag) return 0;
return element_sign(p->y);
}
