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shift ops!

ashok khetan
Ranch Hand

Joined: Jul 29, 2001
Posts: 153
hi,
a simple ?, if the right hand operand in a bit-shift expression is negative(e.g. 10 >> -2), then is there any separate rule for such calculations?
ashok.
Angela Narain
Ranch Hand

Joined: Apr 14, 2001
Posts: 327
The shift distance for integer values is always in the range
of 0 to 31 and for long values in the range of 0 to 63
.So you cannot possibily have a negative shift distance !
Correct me if wrong

Cameron Park
Ranch Hand

Joined: Apr 06, 2001
Posts: 371
I think shifting by negative value is actually shifting by their positive counterparts. For instance, 2>>-1 actually equals 2>>1111 1111 1111 1111, which eqauls 2>>31.
Guoqiao Sun
Ranch Hand

Joined: Jul 18, 2001
Posts: 317
Let's assume the right hand side operand is R, the left side operand is L.
For shift operation L SHIFT R, There will be a % operation if R is not inside the given range.
If L is int, the range is 0-32.
If L is long, the range is 0-64.
In that case, the result of the following
If L is int, R%32
If L is long, R%64

will be replaced for R.
Hope it helps.
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Guoqiao Sun
Sun Certified Programmer for Java™ 2 Platform
Try my mock exam¹ at my homepage.


Guoqiao Sun<br />SCJP2 SCWCD2<br />Creator of <a href="http://www.jiris.com/" target="_blank" rel="nofollow">www.jiris.com</a>, Java resource, mock exam, forum
Dave Vick
Ranch Hand

Joined: May 10, 2001
Posts: 3244
the actual operation carried out on the right hand operand is a bitwise & using a mask of 0x1F for ints and 0x3F for longs. For positive values this is the same as a %32 or %64, but for negative values it behaves differently. What it amounts to, at least in the few tests I've done, is that if the operand is greater than -32(for ints) it adds the operand to 32. So a shift of -4 would actually be a shift of 28. If the operand is less than -32 it will do a %32 on the operand then add the result (a negative number) to 32.
For a line like this:
54 >>> -34;
take -34%32, the result is -2, add -2 to 32, the result is 30, so the line could be written as:
54 >>> 30;
As a follow up, I dont think you'll see anything like this on the test - I didn't and dont know of anyone else who did.
hope this helped


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Dave
Sun Certified Programmer for the Java� 2 Platform


Dave
 
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subject: shift ops!