text: /*
   * Copyright (c) Meta Platforms, Inc. and affiliates.
   *
   * 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.
   */
  
  /**
   * @author Giuseppe Ottaviano <ott@fb.com>
   *
   * Shared utils for BitVectorCoding.h and EliasFanoCoding.h.
   */
  
  #pragma once
  
  #include <stddef.h>
  
  namespace folly {
  namespace compression {
  namespace detail {
  
  /**
   * Helpers to store pointers to forward and skip pointer arrays only
   * if they are used, that is, the quantum is nonzero. If it is 0, the
   * class is empty, and the member is static to keep the syntax valid,
   * thus it will take no space in a derived class thanks to empty base
   * class optimization.
   */
  template <size_t>
  class ForwardPointers {
   protected:
    explicit ForwardPointers(const unsigned char* ptr) : forwardPointers_(ptr) {}
    const unsigned char* const forwardPointers_;
  };
  template <>
  class ForwardPointers<0> {
   protected:
    explicit ForwardPointers(const unsigned char*) {}
    constexpr static const unsigned char* const forwardPointers_{};
  };
  
  template <size_t>
  class SkipPointers {
   protected:
    explicit SkipPointers(const unsigned char* ptr) : skipPointers_(ptr) {}
    const unsigned char* const skipPointers_;
  };
  template <>
  class SkipPointers<0> {
   protected:
    explicit SkipPointers(const unsigned char*) {}
    constexpr static const unsigned char* const skipPointers_{};
  };
  } // namespace detail
  } // namespace compression
  } // namespace folly
  