CODEWITHSUNDEEP
operatorsgo
Zagorax
Zagorax

Reputation: 11900

What do the operators '<<' and '>>' do?

I was following 'A tour of GO` on http://tour.golang.org. The table 15 has some code that I cannot understand. It defines two constants with the following syntax:

const (
    Big = 1<<100
    Small = Big>>99
)

And it's not clear at all to me what it means. I tried to modify the code and run it with different values, to record the change, but I was not able to understand what is going on there.

Then, it uses that operator again on table 24. It defines a variable with the following syntax:

MaxInt uint64 = 1<<64 - 1

And when it prints the variable, it prints:

uint64(18446744073709551615)

Where uint64 is the type. But I can't understand where 18446744073709551615 comes from.

Upvotes: 3

Views: 208

Answers (4)

embedded.kyle
embedded.kyle

Reputation: 11476

It's a logical shift:

every bit in the operand is simply moved a given number of bit positions, and the vacant bit-positions are filled in, usually with zeros

Go Operators:

<<   left shift             integer << unsigned integer
>>   right shift            integer >> unsigned integer

Upvotes: 1

Paolo Falabella
Paolo Falabella

Reputation: 25874

They are Go's bitwise shift operators.

Here's a good explanation of how they work for C (they work in the same way in several languages). Basically 1<<64 - 1 corresponds to 2^64 -1, = 18446744073709551615.

Think of it this way. In decimal if you start from 001 (which is 10^0) and then shift the 1 to the left, you end up with 010, which is 10^1. If you shift it again you end with 100, which is 10^2. So shifting to the left is equivalent to multiplying by 10 as many times as the times you shift.

In binary it's the same thing, but in base 2, so 1<<64 means multiplying by 2 64 times (i.e. 2 ^ 64).

Upvotes: 11

Denys S&#233;guret
Denys S&#233;guret

Reputation: 382454

That's the same as in all languages of the C family : a bit shift.

See http://en.wikipedia.org/wiki/Bitwise_operation#Bit_shifts

This operation is commonly used to multiply or divide an unsigned integer by powers of 2 :

b := a >> 1 // divides by 2

1<<100 is simply 2^100 (that's Big).

1<<64-1 is 2⁶⁴-1, and that's the biggest integer you can represent in 64 bits (by the way you can't represent 1<<64 as a 64 bits int and the point of table 15 is to demonstrate that you can have it in numerical constants anyway in Go).

Upvotes: 7

Cl&#225;udio Ribeiro
Cl&#225;udio Ribeiro

Reputation: 1699

The >> and << are logical shift operations. You can see more about those here:

http://en.wikipedia.org/wiki/Logical_shift

Also, you can check all the Go operators in their webpage

Upvotes: 1

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