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Karu Raj
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Joined: Aug 31, 2005
Posts: 481
Here i don't understand for operator below.Please give me logic to calculate .Are there any formula for the below one .

-5 >> 2 = -2
Stuart Ash
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Joined: Oct 07, 2005
Posts: 637
http://java.sun.com/docs/books/tutorial/java/nutsandbolts/bitwise.html


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Peter Chase
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Joined: Oct 30, 2001
Posts: 1970
Negative numbers in bitwise arithmetic are confusing. You have to work out what the negative numbers look like in binary (two's complement representation). Then the bitwise operation will make sense.

When writing code, I would suggest that you never use negative integer literals (e.g. -2) in a bitwise expression. The clearest representation is usually hexadecimal literals (e.g. 0xFFFFFFFE), because that is very easily translatable to binary in the head of the person reading your code.


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Scott Selikoff
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Joined: Oct 23, 2005
Posts: 3716
    
    5

The formula is to always convert the number to binary 0's and 1's, perform the operation, then convert it back. For exams or homework problems, you're not likely to find a better way to do it by hand.


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Ray Stojonic
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Joined: Aug 08, 2003
Posts: 326
As previously mentioned, negative numbers and bitwise operations are tricky.
I'll use a hit (or nibble...4 bits) to show the steps:

0101 = 5
1010 = ~5 (1s complement - flip all the bits)
1011 = -5 (2s complement - add 1 to 1s complement)

now shift right by 2, carry the sign bit

1101 = shift one
1110 = shift two (result)

so the result is 1110, which is a negative number.

I'll apply 2s complement to translate to an easier to read positive number, keeping in mind that the answer is really negative.

1110 = result
0001 = ~result
0010 = -result = 2 (but we know that it's really negative so: ) -2
 
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