bit-serializer.h

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/*
 * Copyright (c) 2020 Universita' di Firenze, Italy
 *
 * SPDX-License-Identifier: GPL-2.0-only
 *
 * Author: Tommaso Pecorella <tommaso.pecorella@unifi.it>
 */
 
#ifndef BITSERIALIZER_H_
#define BITSERIALIZER_H_
 
#include <cstdint>
#include <vector>
 
namespace ns3
{
 
/**
 * \ingroup packet
 *
 * \brief Bit serializer. See also \sa ns3::BitDeserializer
 *
 * This class helps converting a variable number, variable sized
 * number of bit-boundary fields to its final byte array representation.
 *
 * The typical use-case is:
 * \verbatim
   aaa: A field
   bbb: B field
   ccc: C field
   ddd: D field
   000: padding
 
   |aaaa abbb bbcc cdd0|
 \endverbatim
 *
 *
 * Padding can be automatically added at the end or at the start
 * of the byte blob to reach a multiple of 8 bits.
 * By default the padding is added at the end of the byte blob.
 *
 * This class should be used in two cases:
 *   - When the number of fields is large.
 *   - When the number of fields is variable.
 * In the other cases it's more convenient to use a simple bitmask.
 */
 
class BitSerializer
{
  public:
    BitSerializer();
 
    /**
     * Toggles the padding insertion policy.
     * \param padAtEnd true if the padding have to be inserted at the end of the bit blob.
     */
    void InsertPaddingAtEnd(bool padAtEnd);
 
    /**
     * Pushes a number of bits in the blob.
     * \param value the bits to be inserted.
     * \param significantBits Number of bits to insert.
     */
    void PushBits(uint64_t value, uint8_t significantBits);
 
    /**
     * Get the bytes representation of the blob.
     * Note that this operation  \b automatically add the
     * needed padding at the end (or start) of the blob.
     *
     * \warning {This operation clears the stored data.}
     *
     * \returns The byte representation of the blob.
     */
    std::vector<uint8_t> GetBytes();
 
    /**
     * Get the bytes representation of the blob.
     * Note that this operation  \b automatically add the
     * needed padding at the end (or start) of the blob.
     *
     * \warning {This operation clears the stored data.}
     *
     * \param [out] buffer The buffer where to store the return data.
     * \param [in] size The size of the buffer.
     * \returns The number of bytes actually used in the buffer.
     */
    uint8_t GetBytes(uint8_t* buffer, uint32_t size);
 
  private:
    /**
     * Add the padding at the start of the blob.
     */
    void PadAtStart();
 
    /**
     * Add the padding at the end of the blob.
     */
    void PadAtEnd();
 
    std::vector<bool> m_blob; //!< Blob of serialized bits.
    bool m_padAtEnd;          //!< True if the padding must be added at the end of the blob.
};
 
} // namespace ns3
 
#endif /* BITSERIALIZER_H_ */