title: how bitwise operations are used

panel 1

Binary formats often pack information into bytes very tightly to save space.

Bitwise operations are what you use to encode or decode data into a binary format.

Here’s how and, or, left shift, and right shift are used for encoding and decoding.

panel 2: check/set bit flags

set bit flags with or: x = x | 0x04

check bit flags with and:: if (x & 0x04 != 0) {}

(snippets are C code)

panel 3: bit masking

“bit masking” means using & to set some bits in a number to zero. For example, & 0xFFFF zeroes all except the last 16 bits:

masked = x & 0xFFFF

panel 4: unpack/pack bits

for example, to unpack the leftmost 2 bits of a byte: first_two_bits = x >> 6 (>> is right shift)

for example, to pack 01 into the left 2 bits of a byte: result = (1 << 6) (<< is left shift)

panel 5: checksums and encryption

xor is used for checksums and encryption. Here’s what encrypting with xor in Python looks like:

```

text = b”secret message” for (t, k) in zip(text, key): encrypted += t ^ k ```