What is a bitwise | operator

Question

In lamens terms, what does a bitwise | operator do in Javascript and why is:

8 | 1 ; //9

Duplicate question: http://stackoverflow.com/questions/276706/what-are-bitwise-operators — aug, Dec 09 '12 at 21:46
[MDN docs](https://developer.mozilla.org/en-US/docs/JavaScript/Guide/Expressions_and_Operators#Bitwise_operators) — I Hate Lazy, Dec 09 '12 at 21:46
question just has nothing to do with javascript in particular. — jAndy, Dec 09 '12 at 21:48

Chris Young · Accepted Answer · 2012-12-09T22:12:47.963

8 in binary = 1000
1 in binary = 0001

if you take each binary digit and treat them as if statements (1 being true and 0 being false), you get this:

1 || 0 = 1
0 || 0 = 0
0 || 0 = 0
0 || 1 = 1

and the result is 1001, which is 9 in decimal

If it had been 8 & 1, it would go like this:

1 && 0 = 0
0 && 0 = 0
0 && 0 = 0
0 && 1 = 0

and the result would be 0

Here's a quick example of how you might use these:

You would use the OR operator if you wanted to combine masks -

Using an example of file permissions, you may have the following flags:

1st bit - execute (bin - 001, dec - 1)
2nd bit - write (bin - 010, dec - 2)
3rd bit - read (bin - 100, dec - 4)

If you wanted to create a mask for read and execute, you'd do something like read value | execute value which is 1 | 4 which would give you 5 (101 in bin)

Now you have a mask that you can check a file's permissions to see if it has both of these permissions, using the & operator:

Example file 1 (has read, write, and execute)

Its permission value is 7 (111 in bin): 111 & 101 = 101, so it does have those perms

Example file 2 (has read and write)

Its permission value is 6 (110 in bin): 110 & 101 = 100, so it only has the 100 (4 in dec) perms (read) of the two provided from the mask

score 2 · Answer 2 · answered Dec 09 '12 at 21:46

2

The | operator is a bitwise OR.

8 (base 10) is 1000 (base 2; binary). 1 is 0001

So, 8 | 1 (base 10) is equal to 1000 | 0001 binary, which is 1001 binary, which is 9 (base 10).

answered Dec 09 '12 at 21:46

mah

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score 2 · Answer 3 · answered Dec 09 '12 at 21:47

2

All values on a computer are stored on the hardware in binary format.

| is the OR operater, which combines all bits from both values:

8 - 1000
1 = 0001
--------
9 = 1001

answered Dec 09 '12 at 21:47

Jonathan Wood

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score 1 · Answer 4 · answered Dec 09 '12 at 21:46

Well, in your example, take the binary representations:

8 = 0b1000
1 = 0b0001

Then apply a logical OR to each bit (hence "bitwise"): For each bit, if either one, the other or both is/are 1 then the result is 1, else the result is 0.

8|1 = 0b1001

Which is 9.

score 1 · Answer 5 · answered Dec 09 '12 at 21:48

It takes the binary representation of two numbers, and finds the union ("or") between them.

Consider the two you gave:

binary(8) = 1000
binary(1) = 0001

So, if a bit is 1 in the first number (8) or the second number (1) or if it is 1 in both then it is carried down to the result.

So, 8 | 1 = 9, because 1001 in binary is the result of the "or" operation and is 9 in decimal

What is a bitwise | operator

5 Answers5