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package org.bouncycastle.pqc.math.ntru.polynomial;
import java.math.BigInteger;
import org.bouncycastle.pqc.math.ntru.euclid.BigIntEuclidean;
/**
* A resultant modulo a <code>BigInteger</code>
*/
public class ModularResultant
extends Resultant
{
BigInteger modulus;
ModularResultant(BigIntPolynomial rho, BigInteger res, BigInteger modulus)
{
super(rho, res);
this.modulus = modulus;
}
/**
* Calculates a <code>rho</code> modulo <code>m1*m2</code> from
* two resultants whose <code>rho</code>s are modulo <code>m1</code> and <code>m2</code>.<br/>
* </code>res</code> is set to <code>null</code>.
*
* @param modRes1
* @param modRes2
* @return <code>rho</code> modulo <code>modRes1.modulus * modRes2.modulus</code>, and <code>null</code> for </code>res</code>.
*/
static ModularResultant combineRho(ModularResultant modRes1, ModularResultant modRes2)
{
BigInteger mod1 = modRes1.modulus;
BigInteger mod2 = modRes2.modulus;
BigInteger prod = mod1.multiply(mod2);
BigIntEuclidean er = BigIntEuclidean.calculate(mod2, mod1);
BigIntPolynomial rho1 = (BigIntPolynomial)modRes1.rho.clone();
rho1.mult(er.x.multiply(mod2));
BigIntPolynomial rho2 = (BigIntPolynomial)modRes2.rho.clone();
rho2.mult(er.y.multiply(mod1));
rho1.add(rho2);
rho1.mod(prod);
return new ModularResultant(rho1, null, prod);
}
}
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