ITPEC FE Subject A April 2025 Question 1

Bit Masking with AND — extract specific bits by zeroing others.

To extract the most significant 4 bits of an 8-bit integer, apply AND with a mask:

• •Mask: 11110000 — ones where you want to keep, zeros where you want to clear
• •Example: 10110101 AND 11110000 = 10110000

Why not others:
- (b) NAND with 11110000 — inverts the AND result, gives the opposite
- (c) OR with 00001111 — sets lower 4 bits to 1 instead of clearing them
- (d) XOR with 00001111 — flips lower 4 bits instead of clearing them

Key rule: AND 1 = keep bit, AND 0 = clear bit. This is the standard bit masking technique.

AI-generated — may contain errors