Bitstream

small utility functions for serialization and de-serialization of data

Example Usecase

write or read incoming/outgoing datastreams for protocols

Usage

Writing bits to a stream

uint8_t data[1];
BitstreamWriter bs(data, 1);
bs.put<2>(0b11);
bs.put<3>(0b101);

Reading bits from a stream

uint8_t data[2];
data[0] = 0b00000011;
data[1] = 0b10101110;
...
BitstreamReader bs(data, 2);
uint16_t a = bs.get<10>();
uint16_t b = bs.get<6>();

Reading bits from the middle

uint8_t data[2];
data[0] = 0b00000011;
data[1] = 0b10101110;
...
BitstreamReader bs(data, 2);
uint16_t a = bs.getWithOffset<10>(6);//will get 10 bits starting at bitoffset 6

Example: Parsing RTCP Packets

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
header|V=2|P|    RC   |   PT=SR=200   |             length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                         SSRC of sender                        |
      +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
sender|              NTP timestamp, most significant word             |
info  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |             NTP timestamp, least significant word             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                         RTP timestamp                         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                     sender's packet count                     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                      sender's octet count                     |
      +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+

Writing the code for the parser is now straight forward:

uint8_t rtcp_packet[24];
... // copy data from network receive
BitstreamReader bs(rtcp_packet, 24);
uint8_t version = bs.get<2>();
uint8_t padding = bs.get<1>();
uint8_t rc = bs.get<5>();
uint8_t packetType = bs.get<8>();
uint16_t length = bs.get<16>();
uint32_t ssrc = bs.get<32>();
uint64_t ntpTimestamp = bs.get<64>();
uint32_t rtpTimestamp = bs.get<32>();
uint32_t packetCount = bs.get<32>();
uint32_t octetCount = bs.get<32>();