Bitwise - How can I check if a binary number contains another?

Question

  A  = 110000000    -    384 Blue+Red
  B  = 011000010    -    194 Green+Black+Red

  A & B =   C  = 010000000    -    128 Red

How can I check if B contains all the bits in A and perhaps others? In the case above I would like to get "false".

I'm using XCode & objective-c but that shouldn't matter as far as I know

It's unclear what the colors are refering to in your example. I guess your question is "How can I check if all the bits set to 1 in number A are also set to 1 in number B ?" — franssu
– franssu, Commented Jan 21, 2014 at 11:56

user555045 · Accepted Answer · 2014-01-21 11:52:23Z

17

B contains A if A & B (ie, the intersection) is equal to A:

(a & b) == a

Which is analogous to

a ⊆ b ↔ (a ∩ b) = a

from set theory.

answered Jan 21, 2014 at 11:52

user555045

65.8k6 gold badges95 silver badges181 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Segev Over a year ago

a ⊆ b ↔ (a ∩ b) = a Took me back a few years, thanks!

Mike Seymour · Accepted Answer · 2014-01-21 12:10:12Z

1

If you mean exactly the same bits, the test is A == B.

If you mean B must have all the bits that are set in A, and perhaps others, (A & B) == A.

edited Jan 21, 2014 at 12:10

answered Jan 21, 2014 at 11:47

Mike Seymour

256k30 gold badges467 silver badges658 bronze badges

1 Comment

Mike Seymour Over a year ago

Of course your test won't print anything: your value of B doesn't contain all the bits of your value of A, so you get false as you say you want.

Rahul · Accepted Answer · 2014-01-21 11:48:00Z

0

Use ex-nor

 In C ^ is ex-or operator and ~ is complement, to get ex-nor use ~(a^b)

if a and b are same then all bits will be 1 in ~(a^b)

answered Jan 21, 2014 at 11:48

Rahul

3,5193 gold badges19 silver badges29 bronze badges

2 Comments

Mike Seymour Over a year ago

Or, equivalently, a == b. I don't think the obfuscation adds anything.

Rahul Over a year ago

Definitely. To perform bit wise operator you can use above.

Collectives™ on Stack Overflow

Bitwise - How can I check if a binary number contains another?

3 Answers 3

1 Comment

1 Comment

2 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

1 Comment

1 Comment

2 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related