diff options
Diffstat (limited to 'src/bitfield/bitfield.h')
| -rw-r--r-- | src/bitfield/bitfield.h | 34 |
1 files changed, 33 insertions, 1 deletions
diff --git a/src/bitfield/bitfield.h b/src/bitfield/bitfield.h index 5dd976f0..80f31243 100644 --- a/src/bitfield/bitfield.h +++ b/src/bitfield/bitfield.h @@ -10,6 +10,36 @@ extern "C" { #endif +/* Public: Reads a subset of bits into a uint64_t, right aligned so they may be + * interpreted as a number. + * + * source - the bytes in question. + * source_size - the number of bytes in the source. + * offset - the starting index of the bit field (beginning from 0). + * bit_count - the width of the bit field to extract. This must be less than or + * equal to 64. + * + * Bit fields are positioned according to big-endian bit layout and the data is + * swapped automatically as necessary depending on the compiled architecture. + * + * For example, the bit layout of the value "42" (i.e. 00101010 set at position + * 14 with length 6 is: + * + * 000000000000001010100000000000000000000000000000000000000000000 + * + * and the same value and position but with length 8 is: + * + * 000000000000000010101000000000000000000000000000000000000000000 + * + * Examples + * + * uint64_t value = get_bitfield(data, data_size, 2, 4); + * + * Returns the value of the requested bit field, right aligned in a uint64_t. + */ +uint64_t get_bits(const uint8_t source[], const uint8_t source_length, + const uint16_t offset, const uint16_t bit_count); + /* Public: Return a single nibble from the byte array, with range checking. * * source - the source byte array. @@ -142,7 +172,9 @@ bool set_nibble(const uint16_t nibble_index, const uint8_t value, */ uint16_t bits_to_bytes(uint32_t bits); -/* Private: +/* Public: Return a right aligned bitmask for a uint64_t. + * + * bit_count - the number of bits to mask, right aligned. */ uint64_t bitmask(const uint8_t bit_count); |