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byte to integer conversion -- mock exam qtn

Baskaran Subramani
Ranch Hand

Joined: Jul 30, 2000
Posts: 38
what is the result of the following ..
(byte)0x81 >> 2
the answer given is FFFFFFE0. I do understand that before any shift operation , it will be converted to Int. How come byte 0x81 becomes int 0xFFFFFF81 ? can anyone explain this?
Baskaran.
Sunita Vontel
Ranch Hand

Joined: Aug 28, 2000
Posts: 72
Hey what a coincidence I was just about to tyoe the same question.I will wait for the answer too.
Anonymous
Ranch Hand

Joined: Nov 22, 2008
Posts: 18944
Although you cast 0x81 to byte, it still gets promoted to int before shift. As the highese bit of 0x81 is 1, when it's promoted to int, it takes the 1 and propagates it all the way to the leftmost bit, which oxFFFFFF81.
Hope that helps.
Sunita Vontel
Ranch Hand

Joined: Aug 28, 2000
Posts: 72
Doet it mean when a byte is promoted to an integer , if it is filled with 0 or 1 depends on the leftmost bit??
MahaAdd
Greenhorn

Joined: Aug 28, 2000
Posts: 28
Hi,
i couldn't get u..
can u tell me how could u arrive at oxFFFFFF81 in detail..
thanks
Originally posted by Tian:
Although you cast 0x81 to byte, it still gets promoted to int before shift. As the highese bit of 0x81 is 1, when it's promoted to int, it takes the 1 and propagates it all the way to the leftmost bit, which oxFFFFFF81.
Hope that helps.

Stephanie Grasson
Ranch Hand

Joined: Jun 14, 2000
Posts: 347
Hi all.
I think there may have been a mistake somewhere that propagated through this post.
The original question is:
"what is the result of the following .."
(byte)0x81 >> 2
The correct answer is 0xFFFFFFE0 (NOT 0xFFFFFF81).
You can test it for yourself with the following little program:

Here are the steps to get this result:
0x81 (hexadecimal) is equal to 129 (decimal) which is
10000001 (binary).
So there is the byte value.
Next, before the right shift occurs, the byte is promoted to an int. Because the most significant bit in the original byte is a 1, 1's are used to fill in the upper bits of this integer. So we get this:
11111111 11111111 11111111 10000001
Now we do our right shift by 2, and we get this:
11111111 11111111 11111111 11100000
Finally, we convert the binary to hexidecimal:
1111 1111 1111 1111 1111 1111 1110 0000
F F F F F F E 0
So the answer is:
0xFFFFFFE0
Hope this helps.
Stephanie
Sunita Vontel
Ranch Hand

Joined: Aug 28, 2000
Posts: 72
Thanks stephanie
Baskaran Subramani
Ranch Hand

Joined: Jul 30, 2000
Posts: 38
Thanks stephan.. I got it..
 
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