org.apfloat.internal.Factor3NTTStrategy Maven / Gradle / Ivy

Go to download
package org.apfloat.internal;

import org.apfloat.ApfloatContext;
import org.apfloat.ApfloatRuntimeException;
import org.apfloat.spi.NTTStrategy;
import org.apfloat.spi.Factor3NTTStepStrategy;
import org.apfloat.spi.DataStorage;
import org.apfloat.spi.Util;

/**
 * A transform that implements a 3-point transform on
 * top of another Number Theoretic Transform that does
 * transforms of length 2ⁿ.
 *
 * @see Factor3NTTStepStrategy
 *
 * @since 1.7.0
 * @version 1.7.0
 * @author Mikko Tommila
 */

public class Factor3NTTStrategy
    implements NTTStrategy, Parallelizable
{
    /**
     * Creates a new factor-3 transform strategy on top of an existing transform.
     * The underlying transform needs to be capable of only doing transforms of
     * length 2ⁿ.
     *
     * @param factor2Strategy The underlying transformation strategy, that can be capable of only doing radix-2 transforms.
     */

    public Factor3NTTStrategy(NTTStrategy factor2Strategy)
    {
        this.factor2Strategy = factor2Strategy;
        ApfloatContext ctx = ApfloatContext.getContext();
        this.stepStrategy = ctx.getBuilderFactory().getNTTBuilder().createFactor3NTTSteps();
    }

    public void transform(DataStorage dataStorage, int modulus)
        throws ApfloatRuntimeException
    {
        long length = dataStorage.getSize(),
             power2length = (length & -length);

        if (length > this.stepStrategy.getMaxTransformLength())
        {
            throw new TransformLengthExceededException("Maximum transform length exceeded: " + length + " > " + this.stepStrategy.getMaxTransformLength());
        }

        if (length == power2length)
        {
            // Transform length is a power of two
            this.factor2Strategy.transform(dataStorage, modulus);
        }
        else
        {
            // Transform length is three times a power of two
            assert (length == 3 * power2length);

            DataStorage dataStorage0 = dataStorage.subsequence(0, power2length),
                        dataStorage1 = dataStorage.subsequence(power2length, power2length),
                        dataStorage2 = dataStorage.subsequence(2 * power2length, power2length);

            // Transform the columns
            this.stepStrategy.transformColumns(dataStorage0, dataStorage1, dataStorage2, 0, power2length, power2length, length, false, modulus);

            // Transform the rows
            this.factor2Strategy.transform(dataStorage0, modulus);
            this.factor2Strategy.transform(dataStorage1, modulus);
            this.factor2Strategy.transform(dataStorage2, modulus);
        }
    }

    public void inverseTransform(DataStorage dataStorage, int modulus, long totalTransformLength)
        throws ApfloatRuntimeException
    {
        long length = dataStorage.getSize(),
             power2length = (length & -length);

        if (Math.max(length, totalTransformLength) > this.stepStrategy.getMaxTransformLength())
        {
            throw new TransformLengthExceededException("Maximum transform length exceeded: " + Math.max(length, totalTransformLength) + " > " + this.stepStrategy.getMaxTransformLength());
        }

        if (length == power2length)
        {
            // Transform length is a power of two
            this.factor2Strategy.inverseTransform(dataStorage, modulus, totalTransformLength);
        }
        else
        {
            // Transform length is three times a power of two
            assert (length == 3 * power2length);

            DataStorage dataStorage0 = dataStorage.subsequence(0, power2length),
                        dataStorage1 = dataStorage.subsequence(power2length, power2length),
                        dataStorage2 = dataStorage.subsequence(2 * power2length, power2length);

            // Transform the rows
            this.factor2Strategy.inverseTransform(dataStorage0, modulus, totalTransformLength);
            this.factor2Strategy.inverseTransform(dataStorage1, modulus, totalTransformLength);
            this.factor2Strategy.inverseTransform(dataStorage2, modulus, totalTransformLength);

            // Transform the columns
            this.stepStrategy.transformColumns(dataStorage0, dataStorage1, dataStorage2, 0, power2length, power2length, length, true, modulus);
        }
    }

    public long getTransformLength(long size)
    {
        // Calculates the needed transform length, that is
        // a power of two, or three times a power of two
        return Util.round23up(size);
    }

    public void setParallelRunner(ParallelRunner parallelRunner)
    {
        if (this.factor2Strategy instanceof Parallelizable)
        {
            ((Parallelizable) this.factor2Strategy).setParallelRunner(parallelRunner);
        }
        if (this.stepStrategy instanceof Parallelizable)
        {
            ((Parallelizable) this.stepStrategy).setParallelRunner(parallelRunner);
        }
    }

    private NTTStrategy factor2Strategy;
    private Factor3NTTStepStrategy stepStrategy;
}