Converting from hexa to decimal

[caughtbehind]

I found this on the facebook website - what do you think is the result of this conversion

{ (0xFACEB00C >> 2) in decimal format } @ facebook.com

I know 0x is the symbol for Hexadecimal, but what does ">> 2" do?

Converting FACEB00C into decimal gives 4207849484 - but I'm pretty sure thats not the solution

 

[Chase]

I found the number as well, but I have yet to decipher the ">>2" thing...this is very interesting and rest assured I will post here if I ever figure it out...

::-Chase-::

 

[Chankama]

Bit shift operation. In this case by 2 positions. Which is analogous to dividing the number by 4..

e.g. 0xC >> 2 = 0x1100 >> 2 = 0x11 = 3

or 0xC >> 2 = 12 /4 = 3

 

[jaeusm]

I found the number as well, but I have yet to decipher the ">>2" thing

">>" is the bitwise right shift operator. In this case, it means shift 2 bits to the right, or knock the two right-most (least significant) bits off. For instance, a right shift of 2 bits applied to the value 0xF is 0x3.

0xF = 1111 (binary)
1111 >> 2 = 0011 = 3

Edit: Chankama beat me to it

 

[wilsoniya]

The behavior of >> varies from language to language. In C and Java, >> is the arithmetic right shift operator. I believe the previous two posts by jaeusm and Chankama have almost covered how >> is handled.

You both are correct under intuitive circumstances. In A >> B, you were considering A to be an unsigned integer. If we allow A to be signed, we will run into problems. Take the previous example:

0xF = 1111

If 0xF is unsigned:
1111 >> 2 = 0011
or equivalently:
15 >> 2 = 3.

Unfortunately, C and Java handle arithmetic right shift differently. It seems C forces the number being shifted to be unsigned. Java uses the 'correct' definition of arithmetic right shift and propagates the most significant bit in the result (known as sign extension):

1111 >> 2 = 1111
equivalently in decimal:
-1 >> 2 = -1

or using a different example:
1100 >> 1 = 1110
equivalently in decimal:
-4 >> 1 = -2

Verify: http://en.wikipedia.org/wiki/Bitwise_shift#Shifts_in_C.2C_C.2B.2B.2C_and_Java

Note I am using 2's complement for the representation of the signed integers.

If you ask me, 0xfaceb00c >> 2 is an idiotic thing for the facebook recruiting team to use as an email address. I know they're trying to be clever, but honestly, I hope the engineers exercise a higher degree of finite precision in their daily work than they do in describing their obscure email addresses.