/// <summary>
/// Multiplies the polynomial by another, taking the indices mod N.
/// <para>Does not change this polynomial but returns the result as a new polynomial.
/// Both polynomials must have the same number of coefficients.
/// This method uses the <a href="http://en.wikipedia.org/wiki/Schönhage–Strassen_algorithm"/>
/// Schönhage–Strassen algorithm.</para>
/// </summary>
///
/// <param name="Factor">Multiplication factor</param>
///
/// <returns>Multiplied polynomial</returns>
///
/// <exception cref="CryptoAsymmetricException">Thrown if the two polynomials differ in the number of coefficients</exception>
public BigDecimalPolynomial Multiply(BigIntPolynomial Factor)
{
if (Factor.Coeffs.Length != Coeffs.Length)
{
throw new CryptoAsymmetricException("BigDecimalPolynomial:Multiply", "Number of coefficients must be the same!", new FormatException());
}
BigIntPolynomial poly1 = new BigIntPolynomial(Coeffs.Length);
for (int i = 0; i < Coeffs.Length; i++)
{
poly1.Coeffs[i] = Coeffs[i].UnScaledValue;
}
int scale = Coeffs[0].Scale;
BigIntPolynomial cBigInt = poly1.MultBig(Factor);
BigDecimalPolynomial c = new BigDecimalPolynomial(cBigInt.Coeffs.Length);
for (int i = 0; i < c.Coeffs.Length; i++)
{
c.Coeffs[i] = new BigDecimal(cBigInt.Coeffs[i], scale);
}
return(c);
}
/// <summary>
/// Multiplies the polynomial by an <c>IntegerPolynomial</c>,
/// taking the indices mod <c>N</c>.
/// </summary>
///
/// <param name="Factor">A polynomial factor</param>
///
/// <returns>The product of the two polynomials</returns>
public BigIntPolynomial Multiply(BigIntPolynomial Factor)
{
BigIntPolynomial c = m_f1.Multiply(Factor);
c = m_f2.Multiply(c);
c.Add(m_f3.Multiply(Factor));
return(c);
}
private BigIntPolynomial MultRecursive(BigIntPolynomial Factor)
{
// Karatsuba multiplication
BigInteger[] a = Coeffs;
BigInteger[] b = Factor.Coeffs;
int n = Factor.Coeffs.Length;
if (n <= 1)
{
BigInteger[] c = (BigInteger[])Coeffs.Clone();
for (int i = 0; i < Coeffs.Length; i++)
{
c[i] = c[i].Multiply(Factor.Coeffs[0]);
}
return(new BigIntPolynomial(c));
}
else
{
int n1 = n / 2;
BigIntPolynomial a1 = new BigIntPolynomial(a.CopyOf(n1));
BigIntPolynomial a2 = new BigIntPolynomial(a.CopyOfRange(n1, n));
BigIntPolynomial b1 = new BigIntPolynomial(b.CopyOf(n1));
BigIntPolynomial b2 = new BigIntPolynomial(b.CopyOfRange(n1, n));
BigIntPolynomial A = (BigIntPolynomial)a1.Clone();
A.Add(a2);
BigIntPolynomial B = (BigIntPolynomial)b1.Clone();
B.Add(b2);
BigIntPolynomial c1 = a1.MultRecursive(b1);
BigIntPolynomial c2 = a2.MultRecursive(b2);
BigIntPolynomial c3 = A.MultRecursive(B);
c3.Subtract(c1);
c3.Subtract(c2);
BigIntPolynomial c = new BigIntPolynomial(2 * n - 1);
for (int i = 0; i < c1.Coeffs.Length; i++)
{
c.Coeffs[i] = c1.Coeffs[i];
}
for (int i = 0; i < c3.Coeffs.Length; i++)
{
c.Coeffs[n1 + i] = c.Coeffs[n1 + i].Add(c3.Coeffs[i]);
}
for (int i = 0; i < c2.Coeffs.Length; i++)
{
c.Coeffs[2 * n1 + i] = c.Coeffs[2 * n1 + i].Add(c2.Coeffs[i]);
}
return(c);
}
}
/// <summary>
/// Rounds all coefficients to the nearest integer
/// </summary>
///
/// <returns>A new polynomial with <c>BigInteger</c> coefficients</returns>
public BigIntPolynomial Round()
{
int N = Coeffs.Length;
BigIntPolynomial p = new BigIntPolynomial(N);
for (int i = 0; i < N; i++)
{
p.Coeffs[i] = Coeffs[i].SetScale(0, RoundingModes.HalfEven).ToBigInteger();
}
return(p);
}
/// <summary>
/// Adds another polynomial which can have a different number of coefficients.
/// </summary>
///
/// <param name="B">The polynomial to add</param>
public void Add(BigIntPolynomial B)
{
if (B.Coeffs.Length > Coeffs.Length)
{
int N = Coeffs.Length;
Coeffs = Coeffs.CopyOf(B.Coeffs.Length);
for (int i = N; i < Coeffs.Length; i++)
Coeffs[i] = BigInteger.Zero;
}
for (int i = 0; i < B.Coeffs.Length; i++)
Coeffs[i] = Coeffs[i].Add(B.Coeffs[i]);
}
/// <summary>
/// Multiplies the polynomial by a <c>BigIntPolynomial</c>, taking the indices mod N. Does not
/// change this polynomial but returns the result as a new polynomial.
/// <para>Both polynomials must have the same number of coefficients.</para>
/// </summary>
///
/// <param name="Factor">The polynomial to multiply by</param>
///
/// <returns>The product of the two polynomials</returns>
public BigIntPolynomial Multiply(BigIntPolynomial Factor)
{
BigInteger[] b = Factor.Coeffs;
if (b.Length != m_N)
{
throw new CryptoAsymmetricException("SparseTernaryPolynomial:Multiply", "Number of coefficients must be the same!", new FormatException());
}
BigInteger[] c = new BigInteger[m_N];
for (int i = 0; i < m_N; i++)
{
c[i] = BigInteger.Zero;
}
for (int i = 0; i < m_ones.Length; i++)
{
int j = m_N - 1 - m_ones[i];
for (int k = m_N - 1; k >= 0; k--)
{
c[k] = c[k].Add(b[j]);
j--;
if (j < 0)
{
j = m_N - 1;
}
}
}
for (int i = 0; i < m_negOnes.Length; i++)
{
int j = m_N - 1 - m_negOnes[i];
for (int k = m_N - 1; k >= 0; k--)
{
c[k] = c[k].Subtract(b[j]);
j--;
if (j < 0)
{
j = m_N - 1;
}
}
}
return(new BigIntPolynomial(c));
}
/// <summary>
/// Test the validity of the BigIntPolynomial implementation
/// </summary>
///
/// <returns>State</returns>
public string Test()
{
try
{
BigIntPolynomial a = new BigIntPolynomial(new IntegerPolynomial(new int[] { 4, -1, 9, 2, 1, -5, 12, -7, 0, -9, 5 }));
BigIntPolynomial b = new BigIntPolynomial(new IntegerPolynomial(new int[] { -6, 0, 0, 13, 3, -2, -4, 10, 11, 2, -1 }));
BigIntPolynomial expected = new BigIntPolynomial(new IntegerPolynomial(new int[] { 2, -189, 77, 124, -29, 0, -75, 124, -49, 267, 34 }));
if (!Compare.AreEqual(expected.Coeffs, a.MultSmall(b).Coeffs))
throw new Exception("BigIntPolynomial known value test failed!");
OnProgress(new TestEventArgs("Passed round 1 BigIntPolynomial known value"));
if (!Compare.AreEqual(expected.Coeffs, a.MultBig(b).Coeffs))
throw new Exception("BigIntPolynomial known value test failed!");
OnProgress(new TestEventArgs("Passed round 2 BigIntPolynomial known value"));
Random rng = new Random();
BigInteger[] aCoeffs = new BigInteger[10 + rng.Next(50)];
BigInteger[] bCoeffs = new BigInteger[aCoeffs.Length];
for (int i = 0; i < 3; i++)
{
for (int j = 0; j < aCoeffs.Length; j++)
{
byte[] aArr = new byte[600 + rng.Next(100)];
rng.NextBytes(aArr);
aCoeffs[j] = new BigInteger(aArr);
byte[] bArr = new byte[600 + rng.Next(100)];
rng.NextBytes(bArr);
bCoeffs[j] = new BigInteger(bArr);
}
a = new BigIntPolynomial(aCoeffs);
b = new BigIntPolynomial(bCoeffs);
if (!Compare.AreEqual(a.MultSmall(b).Coeffs, a.MultBig(b).Coeffs))
throw new Exception("BigIntPolynomial coefficient comparison test failed!");
}
OnProgress(new TestEventArgs("Passed BigIntPolynomial coefficient comparison"));
return SUCCESS;
}
catch (Exception Ex)
{
string message = Ex.Message == null ? "" : Ex.Message;
throw new Exception(FAILURE + message);
}
}
/// <summary>
/// Calculates a <c>rho</c> modulo <c>m1*m2</c> from two resultants whose
/// <c>rho</c>s are modulo <c>m1</c> and <c>m2</c>.
/// <para><c>res</c> is set to <c>null</c>.</para>
/// </summary>
///
/// <param name="ModRes1">M1 resultant</param>
/// <param name="ModRes2">M2 resultant</param>
///
/// <returns><c>Rho</c> modulo <c>modRes1.modulus * modRes2.modulus</c>, and <c>null</c> for <c>res</c></returns>
public static ModularResultant CombineRho(ModularResultant ModRes1, ModularResultant ModRes2)
{
BigInteger mod1 = ModRes1.m_modulus;
BigInteger mod2 = ModRes2.m_modulus;
BigInteger prod = mod1.Multiply(mod2);
BigIntEuclidean er = BigIntEuclidean.Calculate(mod2, mod1);
BigIntPolynomial rho1 = ModRes1.Rho.Clone();
rho1.Multiply(er.X.Multiply(mod2));
BigIntPolynomial rho2 = ModRes2.Rho.Clone();
rho2.Multiply(er.Y.Multiply(mod1));
rho1.Add(rho2);
rho1.Mod(prod);
return(new ModularResultant(rho1, null, prod));
}
/// <summary>
/// Adds another polynomial which can have a different number of coefficients.
/// </summary>
///
/// <param name="B">The polynomial to add</param>
public void Add(BigIntPolynomial B)
{
if (B.Coeffs.Length > Coeffs.Length)
{
int N = Coeffs.Length;
Coeffs = Coeffs.CopyOf(B.Coeffs.Length);
for (int i = N; i < Coeffs.Length; i++)
{
Coeffs[i] = BigInteger.Zero;
}
}
for (int i = 0; i < B.Coeffs.Length; i++)
{
Coeffs[i] = Coeffs[i].Add(B.Coeffs[i]);
}
}
/** tests mult(IntegerPolynomial) and mult(BigIntPolynomial) */
private void MultTest()
{
CSPRng rng = new CSPRng();
SparseTernaryPolynomial p1 = SparseTernaryPolynomial.GenerateRandom(1000, 500, 500, rng);
IntegerPolynomial p2 = PolynomialGeneratorForTesting.generateRandom(1000);
IntegerPolynomial prod1 = p1.Multiply(p2);
prod1 = p1.Multiply(p2);
IntegerPolynomial prod2 = p1.Multiply(p2);
if (!Compare.Equals(prod1, prod2))
throw new Exception("SparseTernaryPolynomial multiplication test failed!");
BigIntPolynomial p3 = new BigIntPolynomial(p2);
BigIntPolynomial prod3 = p1.Multiply(p3);
if (!Compare.Equals(new BigIntPolynomial(prod1), prod3))
throw new Exception("SparseTernaryPolynomial multiplication test failed!");
}
/// <summary>
/// Multiplies the polynomial by another, taking the indices mod N.
/// <para>Does not change this polynomial but returns the result as a new polynomial.
/// Both polynomials must have the same number of coefficients.
/// This method is designed for smaller polynomials and uses
/// <a href="http://en.wikipedia.org/wiki/Karatsuba_algorithm">Karatsuba multiplication</a>.</para>
/// </summary>
///
/// <param name="Factor">he polynomial to multiply by</param>
///
/// <returns>The product polynomial</returns>
///
/// <exception cref="CryptoAsymmetricException">Throws if the two polynomials have a different number of coefficients</exception>
public BigIntPolynomial MultSmall(BigIntPolynomial Factor)
{
int N = Coeffs.Length;
if (Factor.Coeffs.Length != N)
{
throw new CryptoAsymmetricException("BigIntPolynomial:Multiply", "Number of coefficients must be the same!", new FormatException());
}
BigIntPolynomial c = MultRecursive(Factor);
if (c.Coeffs.Length > N)
{
for (int k = N; k < c.Coeffs.Length; k++)
{
c.Coeffs[k - N] = c.Coeffs[k - N].Add(c.Coeffs[k]);
}
c.Coeffs = c.Coeffs.CopyOf(N);
}
return(c);
}
private int[] ToIntArray(BigIntPolynomial A, int K)
{
int N = A.Coeffs.Length;
int sign = A.Coeffs[A.Degree()].Signum();
int[] aInt = new int[N * K];
for (int i = N - 1; i >= 0; i--)
{
int[] cArr = SchonhageStrassen.ToIntArray(A.Coeffs[i].Abs());
if (A.Coeffs[i].Signum() * sign < 0)
{
SubShifted(aInt, cArr, i * K);
}
else
{
AddShifted(aInt, cArr, i * K);
}
}
return(aInt);
}
/// <summary>
/// Compare this big integer polynomial to another for equality
/// </summary>
///
/// <param name="Obj">Object to compare</param>
///
/// <returns>True if equal, otherwise false</returns>
public override bool Equals(Object Obj)
{
if (this == Obj)
{
return(true);
}
if (Obj == null)
{
return(false);
}
BigIntPolynomial other = (BigIntPolynomial)Obj;
for (int i = 0; i < Coeffs.Length; i++)
{
if (!Coeffs[i].Equals(other.Coeffs[i]))
{
return(false);
}
}
return(true);
}
/// <summary>
/// Test the validity of the BigDecimalPolynomial implementation
/// </summary>
///
/// <returns>State</returns>
public string Test()
{
try
{
BigDecimalPolynomial a = CreateBigDecimalPolynomial(new int[] { 4, -1, 9, 2, 1, -5, 12, -7, 0, -9, 5 });
BigIntPolynomial b = new BigIntPolynomial(new IntegerPolynomial(new int[] { -6, 0, 0, 13, 3, -2, -4, 10, 11, 2, -1 }));
BigDecimalPolynomial c = a.Multiply(b);
if(!Compare.AreEqual(c.Coeffs, CreateBigDecimalPolynomial(new int[] { 2, -189, 77, 124, -29, 0, -75, 124, -49, 267, 34 }).Coeffs))
throw new Exception("The BigDecimalPolynomial test failed!");
// multiply a polynomial by its inverse modulo 2048 and check that the result is 1
IntegerPolynomial d, dInv;
CSPRng rng = new CSPRng();
do
{
d = DenseTernaryPolynomial.GenerateRandom(1001, 333, 334, rng);
dInv = d.InvertFq(2048);
} while (dInv == null);
d.Mod(2048);
BigDecimalPolynomial e = CreateBigDecimalPolynomial(d.Coeffs);
BigIntPolynomial f = new BigIntPolynomial(dInv);
IntegerPolynomial g = new IntegerPolynomial(e.Multiply(f).Round());
g.ModPositive(2048);
if (!g.EqualsOne())
throw new Exception("The BigDecimalPolynomial test failed!");
OnProgress(new TestEventArgs("Passed BigDecimalPolynomial tests"));
return SUCCESS;
}
catch (Exception Ex)
{
string message = Ex.Message == null ? "" : Ex.Message;
throw new Exception(FAILURE + message);
}
}
/// <summary>
/// Stores the Rho and resultant values
/// </summary>
///
/// <param name="Rho">A polynomial such that <c>res = rho*this + t*(x^n-1) for some integer t</c></param>
/// <param name="Res">A polynomial with <c>x^n-1</c> </param>
public Resultant(BigIntPolynomial Rho, BigInteger Res)
{
this.Rho = Rho;
this.Res = Res;
}
/// <summary>
/// Rounds all coefficients to the nearest integer
/// </summary>
///
/// <returns>A new polynomial with <c>BigInteger</c> coefficients</returns>
public BigIntPolynomial Round()
{
int N = Coeffs.Length;
BigIntPolynomial p = new BigIntPolynomial(N);
for (int i = 0; i < N; i++)
p.Coeffs[i] = Coeffs[i].SetScale(0, RoundingModes.HalfEven).ToBigInteger();
return p;
}
/// <summary>
/// Multiplies the polynomial by another, taking the indices mod N.
/// <para>Does not change this polynomial but returns the result as a new polynomial.
/// Both polynomials must have the same number of coefficients.
/// This method uses the <a href="http://en.wikipedia.org/wiki/Schönhage–Strassen_algorithm"/>
/// Schönhage–Strassen algorithm.</para>
/// </summary>
///
/// <param name="Factor">Multiplication factor</param>
///
/// <returns>Multiplied polynomial</returns>
///
/// <exception cref="NTRUException">Thrown if the two polynomials differ in the number of coefficients</exception>
public BigDecimalPolynomial Multiply(BigIntPolynomial Factor)
{
if (Factor.Coeffs.Length != Coeffs.Length)
throw new CryptoAsymmetricException("BigDecimalPolynomial:Multiply", "Number of coefficients must be the same!", new FormatException());
BigIntPolynomial poly1 = new BigIntPolynomial(Coeffs.Length);
for (int i = 0; i < Coeffs.Length; i++)
poly1.Coeffs[i] = Coeffs[i].UnScaledValue;
int scale = Coeffs[0].Scale;
BigIntPolynomial cBigInt = poly1.MultBig(Factor);
BigDecimalPolynomial c = new BigDecimalPolynomial(cBigInt.Coeffs.Length);
for (int i = 0; i < c.Coeffs.Length; i++)
c.Coeffs[i] = new BigDecimal(cBigInt.Coeffs[i], scale);
return c;
}
/// <summary>
/// Multiplies the polynomial by a <c>BigIntPolynomial</c>, taking the indices mod N. Does not
/// change this polynomial but returns the result as a new polynomial.
/// <para>Both polynomials must have the same number of coefficients.</para>
/// </summary>
///
/// <param name="Factor">The polynomial to multiply by</param>
///
/// <returns>The product of the two polynomials</returns>
public BigIntPolynomial Multiply(BigIntPolynomial Factor)
{
BigInteger[] b = Factor.Coeffs;
if (b.Length != _N)
throw new CryptoAsymmetricException("SparseTernaryPolynomial:Multiply", "Number of coefficients must be the same!", new FormatException());
BigInteger[] c = new BigInteger[_N];
for (int i = 0; i < _N; i++)
c[i] = BigInteger.Zero;
for (int i = 0; i < _ones.Length; i++)
{
int j = _N - 1 - _ones[i];
for (int k = _N - 1; k >= 0; k--)
{
c[k] = c[k].Add(b[j]);
j--;
if (j < 0)
j = _N - 1;
}
}
for (int i = 0; i < _negOnes.Length; i++)
{
int j = _N - 1 - _negOnes[i];
for (int k = _N - 1; k >= 0; k--)
{
c[k] = c[k].Subtract(b[j]);
j--;
if (j < 0)
j = _N - 1;
}
}
return new BigIntPolynomial(c);
}
private int[] ToIntArray(BigIntPolynomial A, int K)
{
int N = A.Coeffs.Length;
int sign = A.Coeffs[A.Degree()].Signum();
int[] aInt = new int[N * K];
for (int i = N - 1; i >= 0; i--)
{
int[] cArr = SchonhageStrassen.ToIntArray(A.Coeffs[i].Abs());
if (A.Coeffs[i].Signum() * sign < 0)
SubShifted(aInt, cArr, i * K);
else
AddShifted(aInt, cArr, i * K);
}
return aInt;
}
private BigIntPolynomial MultRecursive(BigIntPolynomial Factor)
{
// Karatsuba multiplication
BigInteger[] a = Coeffs;
BigInteger[] b = Factor.Coeffs;
int n = Factor.Coeffs.Length;
if (n <= 1)
{
BigInteger[] c = (BigInteger[])Coeffs.Clone();
for (int i = 0; i < Coeffs.Length; i++)
c[i] = c[i].Multiply(Factor.Coeffs[0]);
return new BigIntPolynomial(c);
}
else
{
int n1 = n / 2;
BigIntPolynomial a1 = new BigIntPolynomial(a.CopyOf(n1));
BigIntPolynomial a2 = new BigIntPolynomial(a.CopyOfRange(n1, n));
BigIntPolynomial b1 = new BigIntPolynomial(b.CopyOf(n1));
BigIntPolynomial b2 = new BigIntPolynomial(b.CopyOfRange(n1, n));
BigIntPolynomial A = (BigIntPolynomial)a1.Clone();
A.Add(a2);
BigIntPolynomial B = (BigIntPolynomial)b1.Clone();
B.Add(b2);
BigIntPolynomial c1 = a1.MultRecursive(b1);
BigIntPolynomial c2 = a2.MultRecursive(b2);
BigIntPolynomial c3 = A.MultRecursive(B);
c3.Subtract(c1);
c3.Subtract(c2);
BigIntPolynomial c = new BigIntPolynomial(2 * n - 1);
for (int i = 0; i < c1.Coeffs.Length; i++)
c.Coeffs[i] = c1.Coeffs[i];
for (int i = 0; i < c3.Coeffs.Length; i++)
c.Coeffs[n1 + i] = c.Coeffs[n1 + i].Add(c3.Coeffs[i]);
for (int i = 0; i < c2.Coeffs.Length; i++)
c.Coeffs[2 * n1 + i] = c.Coeffs[2 * n1 + i].Add(c2.Coeffs[i]);
return c;
}
}
/// <summary>
/// Multiplies the polynomial by another, taking the indices mod N.
/// <para>Does not change this polynomial but returns the result as a new polynomial.
/// Both polynomials must have the same number of coefficients.
/// This method is designed for large polynomials and uses Schönhage-Strassen multiplication
/// in combination with <a href="http://en.wikipedia.org/wiki/Kronecker_substitution">Kronecker substitution</a>.
/// See <a href="http://math.stackexchange.com/questions/58946/karatsuba-vs-schonhage-strassen-for-multiplication-of-polynomials#58955">here</a> for details.</para>
/// </summary>
///
/// <param name="Factor">The polynomial to multiply by</param>
///
/// <returns>The product polynomial</returns>
public BigIntPolynomial MultBig(BigIntPolynomial Factor)
{
int N = Coeffs.Length;
// determine #bits needed per coefficient
int logMinDigits = 32 - IntUtils.NumberOfLeadingZeros(N - 1);
int maxLengthA = 0;
for (int i = 0; i < Coeffs.Length; i++)
{
BigInteger coeff = Coeffs[i];
maxLengthA = Math.Max(maxLengthA, coeff.BitLength);
}
int maxLengthB = 0;
for (int i = 0; i < Factor.Coeffs.Length; i++)
{
BigInteger coeff = Factor.Coeffs[i];
maxLengthB = Math.Max(maxLengthB, coeff.BitLength);
}
int k = logMinDigits + maxLengthA + maxLengthB + 1; // in bits
k = (k + 31) / 32; // in ints
// encode each polynomial into an int[]
int aDeg = Degree();
int bDeg = Factor.Degree();
if (aDeg < 0 || bDeg < 0)
{
return(new BigIntPolynomial(N)); // return zero
}
int[] aInt = ToIntArray(this, k);
int[] bInt = ToIntArray(Factor, k);
int[] cInt = SchonhageStrassen.Multiply(aInt, bInt);
// decode poly coefficients from the product
BigInteger _2k = BigInteger.One.ShiftLeft(k * 32);
BigIntPolynomial cPoly = new BigIntPolynomial(N);
for (int i = 0; i < 2 * N - 1; i++)
{
int[] coeffInt = cInt.CopyOfRange(i * k, (i + 1) * k);
BigInteger coeff = SchonhageStrassen.ToBigInteger(coeffInt);
if (coeffInt[k - 1] < 0)
{ // if coeff > 2^(k-1)
coeff = coeff.Subtract(_2k);
// add 2^k to cInt which is the same as subtracting coeff
bool carry = false;
int cIdx = (i + 1) * k;
do
{
cInt[cIdx]++;
carry = cInt[cIdx] == 0;
cIdx++;
} while (carry);
}
cPoly.Coeffs[i % N] = cPoly.Coeffs[i % N].Add(coeff);
}
int aSign = Coeffs[aDeg].Signum();
int bSign = Factor.Coeffs[bDeg].Signum();
if (aSign * bSign < 0)
{
for (int i = 0; i < N; i++)
{
cPoly.Coeffs[i] = cPoly.Coeffs[i].Negate();
}
}
return(cPoly);
}
/// <summary>
/// Multiplies the polynomial by another, taking the indices mod N.
/// <para>Does not change this polynomial but returns the result as a new polynomial.
/// Both polynomials must have the same number of coefficients.
/// This method is designed for large polynomials and uses Schönhage-Strassen multiplication
/// in combination with <a href="http://en.wikipedia.org/wiki/Kronecker_substitution">Kronecker substitution</a>.
/// See <a href="http://math.stackexchange.com/questions/58946/karatsuba-vs-schonhage-strassen-for-multiplication-of-polynomials#58955">here</a> for details.</para>
/// </summary>
///
/// <param name="Factor">The polynomial to multiply by</param>
///
/// <returns>The product polynomial</returns>
public BigIntPolynomial MultBig(BigIntPolynomial Factor)
{
int N = Coeffs.Length;
// determine #bits needed per coefficient
int logMinDigits = 32 - IntUtils.NumberOfLeadingZeros(N - 1);
int maxLengthA = 0;
for (int i = 0; i < Coeffs.Length; i++)
{
BigInteger coeff = Coeffs[i];
maxLengthA = Math.Max(maxLengthA, coeff.BitLength);
}
int maxLengthB = 0;
for (int i = 0; i < Factor.Coeffs.Length; i++)
{
BigInteger coeff = Factor.Coeffs[i];
maxLengthB = Math.Max(maxLengthB, coeff.BitLength);
}
int k = logMinDigits + maxLengthA + maxLengthB + 1; // in bits
k = (k + 31) / 32; // in ints
// encode each polynomial into an int[]
int aDeg = Degree();
int bDeg = Factor.Degree();
if (aDeg < 0 || bDeg < 0)
return new BigIntPolynomial(N); // return zero
int[] aInt = ToIntArray(this, k);
int[] bInt = ToIntArray(Factor, k);
int[] cInt = SchonhageStrassen.Multiply(aInt, bInt);
// decode poly coefficients from the product
BigInteger _2k = BigInteger.One.ShiftLeft(k * 32);
BigIntPolynomial cPoly = new BigIntPolynomial(N);
for (int i = 0; i < 2 * N - 1; i++)
{
int[] coeffInt = cInt.CopyOfRange(i * k, (i + 1) * k);
BigInteger coeff = SchonhageStrassen.ToBigInteger(coeffInt);
if (coeffInt[k - 1] < 0)
{ // if coeff > 2^(k-1)
coeff = coeff.Subtract(_2k);
// add 2^k to cInt which is the same as subtracting coeff
bool carry = false;
int cIdx = (i + 1) * k;
do
{
cInt[cIdx]++;
carry = cInt[cIdx] == 0;
cIdx++;
} while (carry);
}
cPoly.Coeffs[i % N] = cPoly.Coeffs[i % N].Add(coeff);
}
int aSign = Coeffs[aDeg].Signum();
int bSign = Factor.Coeffs[bDeg].Signum();
if (aSign * bSign < 0)
{
for (int i = 0; i < N; i++)
cPoly.Coeffs[i] = cPoly.Coeffs[i].Negate();
}
return cPoly;
}
/// <summary>
/// Multiplies the polynomial by an <c>IntegerPolynomial</c>,
/// taking the indices mod <c>N</c>.
/// </summary>
///
/// <param name="Factor">A polynomial factor</param>
///
/// <returns>The product of the two polynomials</returns>
public BigIntPolynomial Multiply(BigIntPolynomial Factor)
{
BigIntPolynomial c = _f1.Multiply(Factor);
c = _f2.Multiply(c);
c.Add(_f3.Multiply(Factor));
return c;
}
/// <summary>
/// Instantiate the class
/// </summary>
///
/// <param name="Rho">Rho code</param>
/// <param name="Res">Resultant</param>
/// <param name="Modulus">Modulus</param>
public ModularResultant(BigIntPolynomial Rho, BigInteger Res, BigInteger Modulus) :
base(Rho, Res)
{
this.m_modulus = Modulus;
}
/// <summary>
/// Constructs a <c>IntegerPolynomial</c> from a <c>BigIntPolynomial</c>. The two polynomials are independent of each other
/// </summary>
///
/// <param name="P">The original polynomial</param>
public IntegerPolynomial(BigIntPolynomial P)
{
Coeffs = new int[P.Coeffs.Length];
for (int i = 0; i < P.Coeffs.Length; i++)
Coeffs[i] = P.Coeffs[i].ToInt32();
}
// verifies that res=rho*a mod x^n-1 mod p
private void VerifyResultant(IntegerPolynomial a, Resultant r, int p)
{
BigIntPolynomial b = new BigIntPolynomial(a).MultSmall(r.Rho);
b.Mod(BigInteger.ValueOf(p));
for (int j = 1; j < b.Coeffs.Length - 1; j++)
{
if (!Compare.Equals(BigInteger.Zero, b.Coeffs[j]))
throw new Exception("IntegerPolynomialTest VerifyResultant test failed!");
}
if (r.Res.Equals(BigInteger.Zero))
{
if (!Compare.Equals(BigInteger.Zero, b.Coeffs[0].Subtract(b.Coeffs[b.Coeffs.Length - 1])))
throw new Exception("IntegerPolynomialTest VerifyResultant test failed!");
}
else
{
if (!Compare.Equals(BigInteger.Zero, (b.Coeffs[0].Subtract(b.Coeffs[b.Coeffs.Length - 1]).Subtract(r.Res).Mod(BigInteger.ValueOf(p)))))
throw new Exception("IntegerPolynomialTest VerifyResultant test failed!");
}
if (!Compare.Equals(BigInteger.Zero, b.Coeffs[0].Subtract(r.Res).Subtract(b.Coeffs[b.Coeffs.Length - 1].Negate()).Mod(BigInteger.ValueOf(p))))
throw new Exception("IntegerPolynomialTest VerifyResultant test failed!");
}
/// <summary>
/// Multiplies the polynomial with another, taking the indices mod N
/// </summary>
///
/// <param name="Factor">The polynomial factor</param>
///
/// <returns>Multiplied polynomial</returns>
public BigIntPolynomial Multiply(BigIntPolynomial Factor)
{
return new BigIntPolynomial(this).MultSmall(Factor);
}
/// <summary>
/// Multiplies the polynomial by another, taking the indices mod N.
/// <para>Does not change this polynomial but returns the result as a new polynomial.
/// Both polynomials must have the same number of coefficients.
/// This method is designed for smaller polynomials and uses
/// <a href="http://en.wikipedia.org/wiki/Karatsuba_algorithm">Karatsuba multiplication</a>.</para>
/// </summary>
///
/// <param name="Factor">he polynomial to multiply by</param>
///
/// <returns>The product polynomial</returns>
///
/// <exception cref="CryptoAsymmetricException">Throws if the two polynomials have a different number of coefficients</exception>
public BigIntPolynomial MultSmall(BigIntPolynomial Factor)
{
int N = Coeffs.Length;
if (Factor.Coeffs.Length != N)
throw new CryptoAsymmetricException("BigIntPolynomial:Multiply", "Number of coefficients must be the same!", new FormatException());
BigIntPolynomial c = MultRecursive(Factor);
if (c.Coeffs.Length > N)
{
for (int k = N; k < c.Coeffs.Length; k++)
c.Coeffs[k - N] = c.Coeffs[k - N].Add(c.Coeffs[k]);
c.Coeffs = c.Coeffs.CopyOf(N);
}
return c;
}
/// <summary>
/// Stores the Rho and resultant values
/// </summary>
///
/// <param name="Rho">A polynomial such that <c>res = rho*this + t*(x^n-1) for some integer t</c></param>
/// <param name="Res">A polynomial with <c>x^n-1</c> </param>
public Resultant(BigIntPolynomial Rho, BigInteger Res)
{
this.Rho = Rho;
this.Res = Res;
}
/// <summary>
/// Instantiate the class
/// </summary>
///
/// <param name="Rho">Rho code</param>
/// <param name="Res">Resultant</param>
/// <param name="Modulus">Modulus</param>
public ModularResultant(BigIntPolynomial Rho, BigInteger Res, BigInteger Modulus)
: base(Rho, Res)
{
this._modulus = Modulus;
}