Bitfield Utilities in C
===========================

This is a C library with functions to help encode and decode Controller Area
Network (CAN) message payloads or other bitfields.

The header files contain complete function documentation, but to get you
started, here are examples using the API:

## Bitfield Manipulation

The bitfields are stored in `uint8_t[]`.

    uint8_t data[4] = {0x12, 0x34, 0x56, 0x78};
    uint8_t result = get_byte(data, sizeof(data), 0);
    // result = 0x12;
    result = get_nibble(data, sizeof(data), 0);
    // result = 0x1;
    bool success = copy_bits_right_aligned(data, 4, 4, 12, result, 4)
    // success == true
    // result[0] == 0x2
    // result[1] == 0x34

## 8 Byte Helpers

If you are dealing with 8 byte CAN messages as `uint64_t`, there are some
additional functions prefixed with `eightbyte_` that may be faster or more
useful.

### 8 Byte Decoding

    uint64_t data = 0x8000000000000000;
    uint64_t result = get_bitfield(data, 0, 1, false);
    // result == 0x1

    data = 0x0402574d555a0401;
    result = get_bitfield(data, 16, 32, false);
    // result = 0x574d555a;

    data = 0x00000000F34DFCFF;
    result = eightbyte_get_byte(data, 0, false);
    //result = 0x0

    result = eightbyte_get_byte(data, 4, false);
    //result = 0xF3

    result = eightbyte_get_nibble(data, 10, false);
    //result = 0x4;

### 8 Byte Encoding

    uint64_t data = 0;
    fail_unless(set_bit_field(&data, 1, 0, 1));
    uint64_t result = get_bitfield(data, 0, 1, false);
    ck_assert_int_eq(result, 0x1);

### CAN Signal Encoding

The library supports encoding floating point CAN signals as well as booleans
into a uint64_t payload.

    uint64_t payload = bitfield_encode_float(1, 1, 3, 1, 0)
    // payload == 0x1000000000000000

    payload = bitfield_encode_bool(true, 1, 3);
    // payload == 0x1000000000000000

### CAN Signal Decoding

The library supports parsing floating point CAN signals as well as booleans.

    uint64_t payload = 0xeb00000000000000;
    float float_result = bitfield_parse_float(payload,
            2, // starting bit
            4, // width of the signal's field
            1001.0, // transformation factor for the signal value
            -30000.0); // transformation offset for the signal value
    // float_result == -19990.0

    bool bool_result = bitfield_parse_bool(payload,
            0, // starting bit
            1, // width of the signal's field
            1.0, // transformation factor for the signal value
            0); // transformation offset for the signal value
    // bool_result == true

## Testing

The library includes a test suite that uses the `check` C unit test library. It
requires the unit testing library `check`.

    $ make test

You can also see the test coverage if you have `lcov` installed and the
`BROWSER` environment variable set to your choice of web browsers:

    $ BROWSER=google-chrome-stable make coverage

## Authors

Chris Peplin cpeplin@ford.com

## License

Copyright (c) 2013 Ford Motor Company

Licensed under the BSD license.