diff options
Diffstat (limited to 'src/bitfield/8byte.c')
| -rw-r--r-- | src/bitfield/8byte.c | 28 |
1 files changed, 15 insertions, 13 deletions
diff --git a/src/bitfield/8byte.c b/src/bitfield/8byte.c index 3b6b5466..845be8c0 100644 --- a/src/bitfield/8byte.c +++ b/src/bitfield/8byte.c @@ -18,26 +18,28 @@ static uint16_t bits_to_bytes(uint32_t bits) { return byte_count; } -uint64_t get_bit_field(uint64_t source, const uint16_t startBit, +uint64_t get_bit_field(uint64_t source, const uint16_t offset, const uint16_t bit_count, bool big_endian) { - uint8_t result[8] = {0}; + int startByte = offset / CHAR_BIT; + int endByte = (offset + bit_count - 1) / CHAR_BIT; + if(!big_endian) { source = __builtin_bswap64(source); } - copyBitsRightAligned((const uint8_t*)&source, sizeof(source), startBit, - bit_count, result, sizeof(result)); - uint64_t int_result = 0; - if(!big_endian) { - // we need to swap the byte order of the array to get it into a - // uint64_t, but it's been right aligned so we have to be more careful - for(int i = 0; i < bits_to_bytes(bit_count); i++) { - int_result |= result[bits_to_bytes(bit_count) - i - 1] << (CHAR_BIT * i); + uint8_t* bytes = (uint8_t*)&source; + uint64_t ret = bytes[startByte]; + if(startByte != endByte) { + // The lowest byte address contains the most significant bit. + int i; + for(i = startByte + 1; i <= endByte; i++) { + ret = ret << 8; + ret = ret | bytes[i]; } - } else { - int_result = *(uint64_t*)result; } - return int_result; + + ret >>= 8 - find_end_bit(offset + bit_count); + return ret & bitmask(bit_count); } bool set_bit_field(uint64_t* destination, uint64_t value, const uint16_t offset, |