This is a low-level hamming (7,4,3) codec, written in C++ using bitwise operators.

This codec is part of my SOP. The project report, can be read here (in danish).

Features

• Encode bytes
• Encode block of bytes
• Decode bytes
• Decode block of bytes
• Hamming Distance utility function
• Hamming weight utility function
• SEC-DEC extra parity bit for double error detection

Build

If you're on Linux just type make in the root directory and it will build the program and unit tests for you.

Manual:

mkdir -p build/
cd build/
cmake ..

Then to only build program:
make hamming
the unit tests:
make tests
or build all:
make

How to use

You can use this as a library if you remove main.cpp.

• encoding: 4 bits (4 lower bits of a uint8_t), gets encoded to 7 bits (7 lower bits of uint8_t).
• decoding: 7 bits (7 lower bits of a uint8_t), gets decoded to 4 bits (4 lower bits of uint8_t).

Encoding

Encode single chunk

To encode a chunk (4bits) into a 7bit codeword, use the uint8_t encode_hamming7_4chunk(uint8_t) function.

Example:

uint8_t code = 0b0101;
uint8_t codeword = encode_hamming7_4chunk(code); // Should be equal to 0b01001010

Encoding block of data

To encode a block of data, use the int encode_hamming7_4(uint8_t *buffer, uint8_t *codeword, unsigned int size) function.

• buffer: a pointer pointing to the data to be encoded
• codeword: a pointer to a buffer where the codeword should be written to. MUST be at least twice as big as buffer.
• size: the count of elements in buffer to encode.

Example:

uint8_t* data = (uint8_t *) "Here i have some data to be encoded";

// Allocate for codeword buffer (twice as big as data buffer)

size_t data_size = strlen(data);
uint8_t* codeword = (uint8_t *) malloc(sizeof(uint8_t) * data_size * 2);

// Encode block

int rc = encode_hamming7_4(data, codeword, data_size);

Decoding

Decode single chunk

To decode a single codeword (7 bits) to a 4bit code/chunk, use the uint8_t decode_hamming7_4chunk(uint8_t) function.

Example:

uint8_t codeword = 0b01001010;
uint8_t code = decode_hamming7_4chunk(code); // Should be equal to 0b01010

Decode block of data

To decode a block of data, use the void decode_hamming7_4(uint8_t *codewordBuf, uint8_t *outBuffer, unsigned int size) function.

• codewordBuf: a pointer pointing to the data to be decoded
• outBuffer: a pointer to a buffer where the decoded codewords should be written to. MUST at least be as big as half of codewordBuf (size/2).
• size: the count of elements in codewordBuf to decode.

Example:

// The encoded data (in this example it comes from stdin):

std::vector<uint8_t> codewordBuf(std::istreambuf_iterator<char>(std::cin), {});

// Allocate for codeword buffer (twice as big as data buffer)

size_t inputSize = codewordBuf.size();
size_t outSize = inputSize / 2;
uint8_t* decoded_data = (uint8_t *) malloc(sizeof(uint8_t) * outSize);

// Decode block

decode_hamming7_4(codewordBuf.data(), decoded_data, inputSize);