Final answer:
The code n = (packed_data >> 18) & 0xff right-shifts 'packed_data' by 18 bits and then uses a bitwise AND with 0xff to extract the 8 bits (1 byte) now positioned in the least significant bit places.
Step-by-step explanation:
The given line of code n = (packed_data >> 18) & 0xff; performs a bit manipulation operation, specifically in the context of extracting a byte from an integer value.
Firstly, the operation packed_data >> 18 is a right bitwise shift which moves the bits in packed_data 18 positions to the right. This has the effect of discarding the 18 least significant bits and bringing the bits 18 positions deeper into the integer into the least significant positions.
Following this, the operation & 0xff applies a bitwise AND with the hexadecimal value 0xff, which is equivalent to the binary value 11111111. This operation masks out all but the 8 least significant bits of the result from the shift operation. Essentially, it extracts the 8 bits in the integer that were at positions 18 to 25 (inclusive) after the shift, effectively isolating a byte from the original packed_data.