BC_ReedSolomon.cpp

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// Copyright 2014 The PDFium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
 
// Original code copyright 2014 Foxit Software Inc. http://www.foxitsoftware.com
// Original code is licensed as follows:
/*
 * 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.
 */
 
#include "fxbarcode/common/reedsolomon/BC_ReedSolomon.h"
 
#include <memory>
#include <utility>
 
#include "fxbarcode/common/reedsolomon/BC_ReedSolomonGF256.h"
#include "fxbarcode/common/reedsolomon/BC_ReedSolomonGF256Poly.h"
 
CBC_ReedSolomonEncoder::CBC_ReedSolomonEncoder(CBC_ReedSolomonGF256* field)
    : m_field(field) {
  m_cachedGenerators.push_back(std::make_unique<CBC_ReedSolomonGF256Poly>(
      m_field, std::vector<int32_t>{1}));
}
 
CBC_ReedSolomonEncoder::~CBC_ReedSolomonEncoder() = default;
 
CBC_ReedSolomonGF256Poly* CBC_ReedSolomonEncoder::BuildGenerator(
    size_t degree) {
  if (degree >= m_cachedGenerators.size()) {
    CBC_ReedSolomonGF256Poly* lastGenerator = m_cachedGenerators.back().get();
    for (size_t d = m_cachedGenerators.size(); d <= degree; ++d) {
      CBC_ReedSolomonGF256Poly temp_poly(m_field, {1, m_field->Exp(d - 1)});
      auto nextGenerator = lastGenerator->Multiply(&temp_poly);
      if (!nextGenerator)
        return nullptr;
 
      lastGenerator = nextGenerator.get();
      m_cachedGenerators.push_back(std::move(nextGenerator));
    }
  }
  return m_cachedGenerators[degree].get();
}
 
bool CBC_ReedSolomonEncoder::Encode(std::vector<int32_t>* toEncode,
                                    size_t ecBytes) {
  if (ecBytes == 0)
    return false;
 
  if (toEncode->size() <= ecBytes)
    return false;
 
  CBC_ReedSolomonGF256Poly* generator = BuildGenerator(ecBytes);
  if (!generator)
    return false;
 
  size_t dataBytes = toEncode->size() - ecBytes;
  std::vector<int32_t> infoCoefficients(dataBytes);
  for (size_t x = 0; x < dataBytes; x++)
    infoCoefficients[x] = (*toEncode)[x];
 
  CBC_ReedSolomonGF256Poly info(m_field, infoCoefficients);
  auto infoTemp = info.MultiplyByMonomial(ecBytes, 1);
  if (!infoTemp)
    return false;
 
  auto remainder = infoTemp->Divide(generator);
  if (!remainder)
    return false;
 
  const auto& coefficients = remainder->GetCoefficients();
  size_t numZeroCoefficients =
      ecBytes > coefficients.size() ? ecBytes - coefficients.size() : 0;
  for (size_t i = 0; i < numZeroCoefficients; i++)
    (*toEncode)[dataBytes + i] = 0;
  for (size_t y = 0; y < coefficients.size(); y++)
    (*toEncode)[dataBytes + numZeroCoefficients + y] = coefficients[y];
  return true;
}