bit-serializer.cc

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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>
 */
 
#include "ns3/bit-serializer.h"
 
#include "ns3/bit-deserializer.h"
 
#include <iostream>
 
using namespace ns3;
 
// The main purpose of the BitSerializer and bitDeserializer classes is to
// simplify the bit serialization and deserialization in headers, trailers
// and packet bodies.
//
// This is usually performed by using bit masks, which works great if the
// field delimiters are known in advance, and are in a fixed position.
// If the field (i.e., a group of bits) position is dependent from some
// other parameter, then the code is more complex.
// If the field boundary is not even a multiple of a byte, then the problem
// is even more complex.
//
// BitSerializer allows you to "push" bits into a temporary buffer, and then
// extract an array of uint8_t to be used in
// Buffer::Iterator:Write (uint8_t const *buffer, uint32_t size).
//
// Similarly, BitDeserializer can be initialized by an array of uint8_t,
// typically obtained by a Buffer::Iterator:Read (uint8_t *buffer, uint32_t size)
// and then "pop" bits from the underlying buffer.
//
// This example shows the basic operations.
 
int
main()
{
    BitSerializer testBitSerializer1;
 
    // add 7 bits - 0x55 (101 0101)
    testBitSerializer1.PushBits(0x55, 7);
    // add 3 bits - 0x7 (111)
    testBitSerializer1.PushBits(0x7, 3);
    // add 2 bits - 0x0 (00)
    testBitSerializer1.PushBits(0x0, 2);
    // The results is 1010 1011 1100.
    // Adding 4 bits of padding at the end the result is 0xabc0.
 
    std::vector<uint8_t> result = testBitSerializer1.GetBytes();
 
    std::cout << "Result:    ";
    for (std::size_t i = 0; i < result.size(); i++)
    {
        std::cout << std::hex << int(result[i]) << " ";
    }
    std::cout << std::endl;
    std::cout << "Expecting: ab c0" << std::endl;
 
    // Here, instead of printing bits, you typically serialize them using
    // Buffer::Iterator:Write (uint8_t const *buffer, uint32_t size).
    //
    // In this case the number of bits pushed is not a multiple of a byte
    // so the class adds a padding at the end of the buffer.
    // This is the default behaviour.
 
    BitSerializer testBitSerializer2;
 
    // add 7 bits - 0x55 (101 0101)
    testBitSerializer2.PushBits(0x55, 7);
    // add 3 bits - 0x7 (111)
    testBitSerializer2.PushBits(0x7, 3);
    // add 2 bits - 0x0 (00)
    testBitSerializer2.PushBits(0x0, 2);
 
    // Change the class behaviour so to use a padding at the start of the buffer.
    testBitSerializer2.InsertPaddingAtEnd(false);
    // The results is 1010 1011 1100.
    // Adding 4 bits of padding at the start the result is 0xabc.
 
    result = testBitSerializer2.GetBytes();
 
    std::cout << "Result:    ";
    for (std::size_t i = 0; i < result.size(); i++)
    {
        std::cout << std::hex << int(result[i]) << " ";
    }
    std::cout << std::endl;
    std::cout << "Expecting: a bc" << std::endl;
 
    // Here, instead of printing bits, you typically serialize them using
    // Buffer::Iterator:Write (uint8_t const *buffer, uint32_t size).
    //
    // In this case the number of bits pushed is not a multiple of a byte
    // so the class adds a padding at the start of the buffer.
 
    BitDeserializer testBitDeserializer;
    uint8_t test[2];
    test[0] = 0xab;
    test[1] = 0xc0;
 
    // Typically a BitDeserializer will be initialized by an array obtained by
    // Buffer::Iterator:Read (uint8_t *buffer, uint32_t size).
 
    testBitDeserializer.PushBytes(test, 2);
    uint16_t nibble1 = testBitDeserializer.GetBits(7);
    uint8_t nibble2 = testBitDeserializer.GetBits(3);
    uint8_t nibble3 = testBitDeserializer.GetBits(2);
    //  if you deserialize too many bits you'll get an assert.
    //  uint8_t errorNibble = testBitDeserializer.GetBits (6);
 
    std::cout << "Result:    " << std::hex << nibble1 << " " << +nibble2 << " " << +nibble3 << " "
              << std::endl;
    std::cout << "Expecting: 55 7 0" << std::endl;
 
    return 0;
}