http://www.bouncycastle.org/java.html: The Bouncy Castle Crypto package is a Java implementation of cryptographic algorithms. This jar contains JCE provider and lightweight API for the Bouncy Castle Cryptography APIs for JDK 1.5 to JDK 1.8.
  • The Legion of the Bouncy Castle Inc. 
package org.bouncycastle.pqc.math.ntru.polynomial.test;

import java.math.BigDecimal;
import java.security.SecureRandom;

import junit.framework.TestCase;
import org.bouncycastle.pqc.math.ntru.polynomial.BigDecimalPolynomial;
import org.bouncycastle.pqc.math.ntru.polynomial.BigIntPolynomial;
import org.bouncycastle.pqc.math.ntru.polynomial.DenseTernaryPolynomial;
import org.bouncycastle.pqc.math.ntru.polynomial.IntegerPolynomial;

public class BigDecimalPolynomialTest
    extends TestCase
{
    public void testMult()
    {
        BigDecimalPolynomial a = new BigDecimalPolynomial(new BigIntPolynomial(new IntegerPolynomial(new int[]{4, -1, 9, 2, 1, -5, 12, -7, 0, -9, 5})));
        BigDecimalPolynomial b = new BigDecimalPolynomial(new BigIntPolynomial(new IntegerPolynomial(new int[]{-6, 0, 0, 13, 3, -2, -4, 10, 11, 2, -1})));
        BigDecimalPolynomial c = a.mult(b);
        BigDecimal[] expectedCoeffs = new BigDecimalPolynomial(new BigIntPolynomial(new IntegerPolynomial(new int[]{2, -189, 77, 124, -29, 0, -75, 124, -49, 267, 34}))).getCoeffs();

        BigDecimal[] cCoeffs = c.getCoeffs();

        assertEquals(expectedCoeffs.length, cCoeffs.length);
        for (int i = 0; i != cCoeffs.length; i++)
        {
            assertEquals(expectedCoeffs[i], cCoeffs[i]);
        }

        // multiply a polynomial by its inverse modulo 2048 and check that the result is 1
        SecureRandom random = new SecureRandom();
        IntegerPolynomial d, dInv;
        do
        {
            d = DenseTernaryPolynomial.generateRandom(1001, 333, 334, random);
            dInv = d.invertFq(2048);
        }
        while (dInv == null);

        d.mod(2048);
        BigDecimalPolynomial e = new BigDecimalPolynomial(new BigIntPolynomial(d));
        BigIntPolynomial f = new BigIntPolynomial(dInv);
        IntegerPolynomial g = new IntegerPolynomial(e.mult(f).round());
        g.modPositive(2048);
        assertTrue(g.equalsOne());
    }
}