/*******************************************************************************
* Copyright 2012 Analog Devices, Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
********************************************************************************/
package com.analog.lyric.dimple.factorfunctions;
import static java.util.Objects.*;
import com.analog.lyric.dimple.exceptions.DimpleException;
import com.analog.lyric.dimple.factorfunctions.core.FactorFunction;
import com.analog.lyric.dimple.model.domains.FiniteFieldNumber;
import com.analog.lyric.dimple.model.values.FiniteFieldValue;
import com.analog.lyric.dimple.model.values.Value;
/**
* Deterministic finite field (GF(2^n)) multiplication. This is a deterministic directed factor.
* <p>
* The variables are ordered as follows in the argument list:
* <ol>
* <li>Output (FiniteFieldVariable; Output = input1 * input2)
* <li>Input1 (FiniteFieldVariable)
* <li>Input2 (FiniteFieldVariable)
* </ol>
* @since 0.05
*/
public class FiniteFieldMult extends FactorFunction
{
@Override
public final double evalEnergy(Value[] arguments)
{
// Allow one constant input
final FiniteFieldNumber result = requireNonNull((FiniteFieldNumber)arguments[0].getObject());
final Value arg1 = arguments[1];
final FiniteFieldNumber input1 = (arg1 instanceof FiniteFieldValue) ? arg1.getFiniteField() : result.cloneWithNewValue(arg1.getInt());
final Value arg2 = arguments[2];
final FiniteFieldNumber input2 = (arg2 instanceof FiniteFieldValue) ? arg2.getFiniteField() : result.cloneWithNewValue(arg2.getInt());
if (!result.isCompatible(input1) || !result.isCompatible(input2))
throw new DimpleException("Primitive polynomials must match.");
final FiniteFieldNumber computedResult = finiteFieldProduct(input1, input2);
return (computedResult.isEqual(result)) ? 0 : Double.POSITIVE_INFINITY;
}
@Override
public final boolean isDirected() {return true;}
@Override
public final int[] getDirectedToIndices() {return new int[]{0};}
@Override
public final boolean isDeterministicDirected() {return true;}
@Override
public final void evalDeterministic(Value[] arguments)
{
// Allow one constant input
final Value arg1Value = arguments[1];
final Value arg2Value = arguments[2];
final Object arg1 = requireNonNull(arg1Value.getObject());
final Object arg2 = requireNonNull(arg2Value.getObject());
final FiniteFieldNumber input1 = (arg1 instanceof FiniteFieldNumber) ? (FiniteFieldNumber)arg1 : ((FiniteFieldNumber)arg2).cloneWithNewValue(arg1Value.getInt());
final FiniteFieldNumber input2 = (arg2 instanceof FiniteFieldNumber) ? (FiniteFieldNumber)arg2 : ((FiniteFieldNumber)arg1).cloneWithNewValue(arg2Value.getInt());
if (!input1.isCompatible(input2))
throw new DimpleException("Primitive polynomials must match.");
arguments[0].setFiniteField(finiteFieldProduct(input1, input2)); // Replace the output value
}
private final FiniteFieldNumber finiteFieldProduct(FiniteFieldNumber input1, FiniteFieldNumber input2)
{
int x = input1.intValue();
int y = input2.intValue();
int n = input1.getN();
int prim_poly = input1.getPrimativePolynomial();
int z=0;
/* Convolve x and y as bit strings mod 2 */
for (int i = 0; i < n; i++)
if ((1 & (x>>i)) == 1)
z ^= (y<<i);
/* Take any "extra" bits located at bit n or higher and fold it back down */
for (int i = 2*n; i>=n; i--)
if ((1 & (z>>i)) == 1)
z ^= (prim_poly<<(i-n));
return input1.cloneWithNewValue(z);
}
}