CODEWITHSUNDEEP
javaprimitive-types
user1467855
user1467855

Reputation: 3993

What does bitwise & 0x3FF do?

Can someone explain the following line of code? Particularly, I don't get what (short) x & 0x3FF does?

int num = ... //some number.
return (short) num & 0x3FF;

Upvotes: 5

Views: 9194

Answers (5)

Bohemian
Bohemian

Reputation: 425198

The java operator & is a "bitwise AND", meaning each bit of the two operands is ANDed together, leaving a 1 if both corresponding bits are 1.

0x3ff is binary 1111111111, so ANDing with that will mask all but the lowest ten bits.

The cast to short (a 16-bit number format) has no effect.

Upvotes: 1

sangupta
sangupta

Reputation: 2406

It retains only the right-most 10 bits.

Upvotes: 0

Prashant Kumar
Prashant Kumar

Reputation: 22579

Converting hex to binary, 0x3FF == 0b1111111111.

The & performs bitwise AND, so it will only keep the low bits if they were set to be on.
This guarantees that the answer is no larger than 0x3FF == 1023, so the answer is saved into a short, since we know it'll fit in one.

Upvotes: 3

Petar Ivanov
Petar Ivanov

Reputation: 93050

0x3FF is the number 1111111111 in binary, which means that the bitwize AND with it would give you the last 10 bits of num.

Upvotes: 8

Tim
Tim

Reputation: 35943

It zeros out the top bits of the number, such that the result is always between 0 and 1023. It's essentially the same thing as modulo(num, 1024) (for positive values of num).

Without seeing a broader context it's impossible to know why this is here, but that's what it does.

Upvotes: 10

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