itextpdf.jar is a component in iText 5 Java library to provide core functionalities. iText Java library allows you to generate and manage PDF documents.

The Source Code files are provided at iText GitHub site.

You can compile it to generate your JAR file, using pom.xml as the build configuration file.

The source code of itextpdf-5.5.14.jar is provided below:

⏎ com/itextpdf/text/pdf/qrcode/GF256.java

/*
 * Copyright 2007 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.
 */

package com.itextpdf.text.pdf.qrcode;

/**
 * <p>This class contains utility methods for performing mathematical operations over
 * the Galois Field GF(256). Operations use a given primitive polynomial in calculations.</p>
 *
 * <p>Throughout this package, elements of GF(256) are represented as an <code>int</code>
 * for convenience and speed (but at the cost of memory).
 * Only the bottom 8 bits are really used.</p>
 *
 * @author Sean Owen
 * @since 5.0.2
 */
public final class GF256 {

  public static final GF256 QR_CODE_FIELD = new GF256(0x011D); // x^8 + x^4 + x^3 + x^2 + 1
  public static final GF256 DATA_MATRIX_FIELD = new GF256(0x012D); // x^8 + x^5 + x^3 + x^2 + 1

  private final int[] expTable;
  private final int[] logTable;
  private final GF256Poly zero;
  private final GF256Poly one;

  /**
   * Create a representation of GF(256) using the given primitive polynomial.
   *
   * @param primitive irreducible polynomial whose coefficients are represented by
   *  the bits of an int, where the least-significant bit represents the constant
   *  coefficient
   */
  private GF256(int primitive) {
    expTable = new int[256];
    logTable = new int[256];
    int x = 1;
    for (int i = 0; i < 256; i++) {
      expTable[i] = x;
      x <<= 1; // x = x * 2; we're assuming the generator alpha is 2
      if (x >= 0x100) {
        x ^= primitive;
      }
    }
    for (int i = 0; i < 255; i++) {
      logTable[expTable[i]] = i;
    }
    // logTable[0] == 0 but this should never be used
    zero = new GF256Poly(this, new int[]{0});
    one = new GF256Poly(this, new int[]{1});
  }

  GF256Poly getZero() {
    return zero;
  }

  GF256Poly getOne() {
    return one;
  }

  /**
   * @return the monomial representing coefficient * x^degree
   */
  GF256Poly buildMonomial(int degree, int coefficient) {
    if (degree < 0) {
      throw new IllegalArgumentException();
    }
    if (coefficient == 0) {
      return zero;
    }
    int[] coefficients = new int[degree + 1];
    coefficients[0] = coefficient;
    return new GF256Poly(this, coefficients);
  }

  /**
   * Implements both addition and subtraction -- they are the same in GF(256).
   *
   * @return sum/difference of a and b
   */
  static int addOrSubtract(int a, int b) {
    return a ^ b;
  }

  /**
   * @return 2 to the power of a in GF(256)
   */
  int exp(int a) {
    return expTable[a];
  }

  /**
   * @return base 2 log of a in GF(256)
   */
  int log(int a) {
    if (a == 0) {
      throw new IllegalArgumentException();
    }
    return logTable[a];
  }

  /**
   * @return multiplicative inverse of a
   */
  int inverse(int a) {
    if (a == 0) {
      throw new ArithmeticException();
    }
    return expTable[255 - logTable[a]];
  }

  /**
   * @param a
   * @param b
   * @return product of a and b in GF(256)
   */
  int multiply(int a, int b) {
    if (a == 0 || b == 0) {
      return 0;
    }
    if (a == 1) {
      return b;
    }
    if (b == 1) {
      return a;
    }
    return expTable[(logTable[a] + logTable[b]) % 255];
  }

}

⏎ com/itextpdf/text/pdf/qrcode/GF256.java

Or download all of them as a single archive file:

File name: itextpdf-5.5.14-fyi.zip
File size: 2163839 bytes
Release date: 2009-10-09
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