Bit Masking

mental model using the name

The word mask in the name helps to understand and remember the concept.

Here, mask means a bit pattern that hides all but certain bits. We extract the values from the bit positions we want.

Why bit masking is needed

Bit masking avoids parsing the whole bit sequence to extract data. That's costly.

For example, file permissions are stored for 3 scopes: owner, group, and others. Without a bit mask, the client must parse the whole permission sequence to get one scope.

With a bitmask, you AND the actual bits with the mask. The mask has ones at the positions you want. The result then lets you read those bits directly.