/*
* Copyright 2012 ZXing authors
*
* 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.
*/
using System;
using System.Text;
namespace ZXing.PDF417.Internal.EC
{
/// <summary>
/// <see cref="ZXing.Common.ReedSolomon.GenericGFPoly"/>
/// </summary>
/// <author>Sean Owen</author>
internal sealed class ModulusPoly
{
private readonly ModulusGF field;
private readonly int[] coefficients;
public ModulusPoly(ModulusGF field, int[] coefficients)
{
if (coefficients.Length == 0)
{
throw new ArgumentException();
}
this.field = field;
int coefficientsLength = coefficients.Length;
if (coefficientsLength > 1 && coefficients[0] == 0)
{
// Leading term must be non-zero for anything except the constant polynomial "0"
int firstNonZero = 1;
while (firstNonZero < coefficientsLength && coefficients[firstNonZero] == 0)
{
firstNonZero++;
}
if (firstNonZero == coefficientsLength)
{
this.coefficients = new int[]{0};
}
else
{
this.coefficients = new int[coefficientsLength - firstNonZero];
Array.Copy(coefficients,
firstNonZero,
this.coefficients,
0,
this.coefficients.Length);
}
}
else
{
this.coefficients = coefficients;
}
}
/// <summary>
/// Gets the coefficients.
/// </summary>
/// <value>The coefficients.</value>
internal int[] Coefficients
{
get { return coefficients; }
}
/// <summary>
/// degree of this polynomial
/// </summary>
internal int Degree
{
get
{
return coefficients.Length - 1;
}
}
/// <summary>
/// Gets a value indicating whether this instance is zero.
/// </summary>
/// <value>true if this polynomial is the monomial "0"
/// </value>
internal bool isZero
{
get { return coefficients[0] == 0; }
}
/// <summary>
/// coefficient of x^degree term in this polynomial
/// </summary>
/// <param name="degree">The degree.</param>
/// <returns>coefficient of x^degree term in this polynomial</returns>
internal int getCoefficient(int degree)
{
return coefficients[coefficients.Length - 1 - degree];
}
/// <summary>
/// evaluation of this polynomial at a given point
/// </summary>
/// <param name="a">A.</param>
/// <returns>evaluation of this polynomial at a given point</returns>
internal int evaluateAt(int a)
{
if (a == 0)
{
// Just return the x^0 coefficient
return getCoefficient(0);
}
int result = 0;
if (a == 1)
{
// Just the sum of the coefficients
foreach (var coefficient in coefficients)
{
result = field.add(result, coefficient);
}
return result;
}
result = coefficients[0];
int size = coefficients.Length;
for (int i = 1; i < size; i++)
{
result = field.add(field.multiply(a, result), coefficients[i]);
}
return result;
}
/// <summary>
/// Adds another Modulus
/// </summary>
/// <param name="other">Other.</param>
internal ModulusPoly add(ModulusPoly other)
{
if (!field.Equals(other.field))
{
throw new ArgumentException("ModulusPolys do not have same ModulusGF field");
}
if (isZero)
{
return other;
}
if (other.isZero)
{
return this;
}
int[] smallerCoefficients = this.coefficients;
int[] largerCoefficients = other.coefficients;
if (smallerCoefficients.Length > largerCoefficients.Length)
{
int[] temp = smallerCoefficients;
smallerCoefficients = largerCoefficients;
largerCoefficients = temp;
}
int[] sumDiff = new int[largerCoefficients.Length];
int lengthDiff = largerCoefficients.Length - smallerCoefficients.Length;
// Copy high-order terms only found in higher-degree polynomial's coefficients
Array.Copy(largerCoefficients, 0, sumDiff, 0, lengthDiff);
for (int i = lengthDiff; i < largerCoefficients.Length; i++)
{
sumDiff[i] = field.add(smallerCoefficients[i - lengthDiff], largerCoefficients[i]);
}
return new ModulusPoly(field, sumDiff);
}
/// <summary>
/// Subtract another Modulus
/// </summary>
/// <param name="other">Other.</param>
internal ModulusPoly subtract(ModulusPoly other)
{
if (!field.Equals(other.field))
{
throw new ArgumentException("ModulusPolys do not have same ModulusGF field");
}
if (other.isZero)
{
return this;
}
return add(other.getNegative());
}
/// <summary>
/// Multiply by another Modulus
/// </summary>
/// <param name="other">Other.</param>
internal ModulusPoly multiply(ModulusPoly other)
{
if (!field.Equals(other.field))
{
throw new ArgumentException("ModulusPolys do not have same ModulusGF field");
}
if (isZero || other.isZero)
{
return field.Zero;
}
int[] aCoefficients = this.coefficients;
int aLength = aCoefficients.Length;
int[] bCoefficients = other.coefficients;
int bLength = bCoefficients.Length;
int[] product = new int[aLength + bLength - 1];
for (int i = 0; i < aLength; i++)
{
int aCoeff = aCoefficients[i];
for (int j = 0; j < bLength; j++)
{
product[i + j] = field.add(product[i + j], field.multiply(aCoeff, bCoefficients[j]));
}
}
return new ModulusPoly(field, product);
}
/// <summary>
/// Returns a Negative version of this instance
/// </summary>
internal ModulusPoly getNegative()
{
int size = coefficients.Length;
int[] negativeCoefficients = new int[size];
for (int i = 0; i < size; i++)
{
negativeCoefficients[i] = field.subtract(0, coefficients[i]);
}
return new ModulusPoly(field, negativeCoefficients);
}
/// <summary>
/// Multiply by a Scalar.
/// </summary>
/// <param name="scalar">Scalar.</param>
internal ModulusPoly multiply(int scalar)
{
if (scalar == 0)
{
return field.Zero;
}
if (scalar == 1)
{
return this;
}
int size = coefficients.Length;
int[] product = new int[size];
for (int i = 0; i < size; i++)
{
product[i] = field.multiply(coefficients[i], scalar);
}
return new ModulusPoly(field, product);
}
/// <summary>
/// Multiplies by a Monomial
/// </summary>
/// <returns>The by monomial.</returns>
/// <param name="degree">Degree.</param>
/// <param name="coefficient">Coefficient.</param>
internal ModulusPoly multiplyByMonomial(int degree, int coefficient)
{
if (degree < 0)
{
throw new ArgumentException();
}
if (coefficient == 0)
{
return field.Zero;
}
int size = coefficients.Length;
int[] product = new int[size + degree];
for (int i = 0; i < size; i++)
{
product[i] = field.multiply(coefficients[i], coefficient);
}
return new ModulusPoly(field, product);
}
/*
/// <summary>
/// Divide by another modulus
/// </summary>
/// <param name="other">Other.</param>
internal ModulusPoly[] divide(ModulusPoly other)
{
if (!field.Equals(other.field))
{
throw new ArgumentException("ModulusPolys do not have same ModulusGF field");
}
if (other.isZero)
{
throw new DivideByZeroException();
}
ModulusPoly quotient = field.Zero;
ModulusPoly remainder = this;
int denominatorLeadingTerm = other.getCoefficient(other.Degree);
int inverseDenominatorLeadingTerm = field.inverse(denominatorLeadingTerm);
while (remainder.Degree >= other.Degree && !remainder.isZero)
{
int degreeDifference = remainder.Degree - other.Degree;
int scale = field.multiply(remainder.getCoefficient(remainder.Degree), inverseDenominatorLeadingTerm);
ModulusPoly term = other.multiplyByMonomial(degreeDifference, scale);
ModulusPoly iterationQuotient = field.buildMonomial(degreeDifference, scale);
quotient = quotient.add(iterationQuotient);
remainder = remainder.subtract(term);
}
return new ModulusPoly[] { quotient, remainder };
}
*/
/// <summary>
/// Returns a <see cref="System.String"/> that represents the current <see cref="ZXing.PDF417.Internal.EC.ModulusPoly"/>.
/// </summary>
/// <returns>A <see cref="System.String"/> that represents the current .
public override String ToString()
{
var result = new StringBuilder(8 * Degree);
for (int degree = Degree; degree >= 0; degree--)
{
int coefficient = getCoefficient(degree);
if (coefficient != 0)
{
if (coefficient < 0)
{
result.Append(" - ");
coefficient = -coefficient;
}
else
{
if (result.Length > 0)
{
result.Append(" + ");
}
}
if (degree == 0 || coefficient != 1)
{
result.Append(coefficient);
}
if (degree != 0)
{
if (degree == 1)
{
result.Append('x');
}
else
{
result.Append("x^");
result.Append(degree);
}
}
}
}
return result.ToString();
}
}
}
