Operator Bitwise Right

Question

Hello

Conducting some studies on PHP I came across bitwise and until then all its operations has not been anything difficult, just the one of the right shift

An exmeplo I took and I still don’t understand was this:

print(4>>6); //onde o resultado final é igual a zero

And looking at a book I realized the following calculation for this expression:

4/2^6
2^6 = 2*2*2*2*2*2=64
64/4 = 0,06 

That in the case would be equal to zero, which is the result that php returns me, although I think it should give 16. Could someone explain this logic to me?

Answer 1

Dividend is 4 and the divisor is 64.

In the expression is reversed.

The right then is 4 / 64, whose result is 0.0625

Answer 2

See the 4 in base 2:

00000100

Now let’s move it once to the right ( 4 >> 1 ):

00000010

If we moved twice ( 4 >> 2 ):

00000001

Moving 6 houses, the bit was "gone", so the result 0.

Look at the left shift, I’ll take the number 6 as an example, and move twice:

00000110 (6)

00011000 (6<<2 = 24)

In short:

• when you shift to right, is divided by 2 at every step.

• when it moves to left, is multiplying by 2 at every step.

See more details here:

How the bit offset in C/C works++?