void SFBerlekamp(vec_ZZ_pX& factors, const ZZ_pX& ff, long verbose)
{
ZZ_pX f = ff;
if (!IsOne(LeadCoeff(f)))
Error("SFBerlekamp: bad args");
if (deg(f) == 0) {
factors.SetLength(0);
return;
}
if (deg(f) == 1) {
factors.SetLength(1);
factors[0] = f;
return;
}
double t;
const ZZ& p = ZZ_p::modulus();
long n = deg(f);
ZZ_pXModulus F;
build(F, f);
ZZ_pX g, h;
if (verbose) { cerr << "computing X^p..."; t = GetTime(); }
PowerXMod(g, p, F);
if (verbose) { cerr << (GetTime()-t) << "\n"; }
vec_long D;
long r;
vec_ZZVec M;
if (verbose) { cerr << "building matrix..."; t = GetTime(); }
BuildMatrix(M, n, g, F, verbose);
if (verbose) { cerr << (GetTime()-t) << "\n"; }
if (verbose) { cerr << "diagonalizing..."; t = GetTime(); }
NullSpace(r, D, M, verbose);
if (verbose) { cerr << (GetTime()-t) << "\n"; }
if (verbose) cerr << "number of factors = " << r << "\n";
if (r == 1) {
factors.SetLength(1);
factors[0] = f;
return;
}
if (verbose) { cerr << "factor extraction..."; t = GetTime(); }
vec_ZZ_p roots;
RandomBasisElt(g, D, M);
MinPolyMod(h, g, F, r);
if (deg(h) == r) M.kill();
FindRoots(roots, h);
FindFactors(factors, f, g, roots);
ZZ_pX g1;
vec_ZZ_pX S, S1;
long i;
while (factors.length() < r) {
if (verbose) cerr << "+";
RandomBasisElt(g, D, M);
S.kill();
for (i = 0; i < factors.length(); i++) {
const ZZ_pX& f = factors[i];
if (deg(f) == 1) {
append(S, f);
continue;
}
build(F, f);
rem(g1, g, F);
if (deg(g1) <= 0) {
append(S, f);
continue;
}
MinPolyMod(h, g1, F, min(deg(f), r-factors.length()+1));
FindRoots(roots, h);
S1.kill();
FindFactors(S1, f, g1, roots);
append(S, S1);
}
swap(factors, S);
}
if (verbose) { cerr << (GetTime()-t) << "\n"; }
if (verbose) {
cerr << "degrees:";
long i;
for (i = 0; i < factors.length(); i++)
cerr << " " << deg(factors[i]);
cerr << "\n";
}
}
//=====================================================
BerlekampFactorization::BerlekampFactorization(
PolyOvrPrimeField *orig_poly )
{
int k, r, s;
int poly_idx;
int deg = orig_poly->MaxDegree();
int prime_char = orig_poly->PrimeBase();
matrix_pf *v;
PolyOvrPrimeField **polys;
int num_facs = 1;
int num_polys;
Factors = new PolyOvrPrimeField*[1];
Factors[0] = orig_poly;
for(int iter=0; iter<1; iter++)
{
num_polys = num_facs;
polys = new PolyOvrPrimeField*[num_polys];
for( poly_idx=0; poly_idx<num_polys; poly_idx++)
{
polys[poly_idx] = Factors[poly_idx];
int yydeg = (polys[poly_idx])->MaxDegree();
// delete (Factors[poly_idx]);
} // end of loop over poly_idx
delete[] Factors;
num_facs = 0;
Factors = new PolyOvrPrimeField*[20];
for( poly_idx=0; poly_idx<num_polys; poly_idx++)
{
//int xxdeg = (polys[poly_idx])->MaxDegree();
//if(xxdeg == 7) continue;
B_Mtx = new BerlekampMatrix( polys[poly_idx] );
// Row k corresponds to the term x**(k*p) where p is the
// characteristic of the prime field over which the polynomial
// is to be factored.
//-----------------------------------------------------
// Compute null space of B matrix
v = NullSpace(B_Mtx, &r);
//----------------------------------------------------
// Find factors
//DebugFile << "rrr = " << r << endl;
R = r;
//
// The original polynomial should factor into r irreducible
// polynomials. However each iteration of the Berlekamp
// factorization will only factor the original polynomial
// into p polynomials (which, in general, may be reducible)
// where p is the prime characteristic of the field from
// which the coefficients are drawn. Additional iterations
// can be performed until all r irreducible factors are found.
// Factors = new PolyOvrPrimeField*[r];
//PolyOvrPrimeField factor_poly;
//Factors[0] = new PolyOvrPrimeField;
for(k=1; k<2; k++)
{
//--------------------------------------------------------------
// Use the row 1 elements of v as coefficients for a polynomial
PolyOvrPrimeField *work_poly = new PolyOvrPrimeField( prime_char,
&((*v)[k]));
//DebugFile << "work_poly:" << endl;
//work_poly->DumpToStream(&DebugFile);
//DebugFile << "poly:" << endl;
//polys[poly_idx]->DumpToStream(&DebugFile);
for(s=0; s<prime_char; s++)
{
Factors[num_facs] = &(EuclideanAlgorithm( polys[poly_idx], work_poly ) );
//DebugFile << "factor_poly (for k=" << k <<", s=" << s << "):" << endl;
//(Factors[num_facs])->DumpToStream(&DebugFile);
(*work_poly) -= PrimeFieldElem( prime_char, 1 );
num_facs++;
}
delete work_poly;
delete B_Mtx;
delete v;
} // end of loop over k
} // end of loop over poly_idx
} // end of loop over iter
}
