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 07052011, 05:51 AM #1Member
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Feeling a lil bitstupid with this bitwise.
I have a function written in JavaScript that deals with unsigned longs (guess you could call them since JS has no var types). Anyhow I'm porting the project to Java and the same bitshifting operations are not working as expected. Here is an example.
JavaScript:
1509786213^3738585502=2027172869
Java
1509786213^3738585502=2267794427
I can't get any bitshift operation to change the number so the right number. Any ideas? Thanks ahead of time.
 07052011, 06:11 AM #2
Your problem is that in Java by default literal values are ints. 3738585502 is larger than the largest int value. You can try making your values longs by placing an 'L' after the number: 3738585502L
 07052011, 11:22 AM #3JavaScript:
1509786213^3738585502=2027172869
I have as book in front of me calculating 2^112131 (a Mersenne prime) and it needs two pages to print the result. The BigInteger class has a powmethod but only for intarguments.No bug ever had to calculate its fitnessfunction.
 07052011, 11:38 AM #4
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I think the OP means an exlusiveor operation by the '^' symbol; what I don't understand is how Java (according to the OP) calculates the expression as:
1509786213^3738585502=2267794427
I tried it but my result is negative (as the Javascript result) as well.
kind regards,
Jos
ps. only the exponent needs to be an int, that mantissa is a BigInteger so your Mersenne prime can be calculated by a BigInteger object ;)I have the stamina of a seal; I lie on the beach instead of running on it.
 07052011, 12:15 PM #5Senior Member
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 07052011, 12:34 PM #6
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 07052011, 01:07 PM #7
@Jos
Eating sand again. (Working too much with my own calculator that interprets me fine )
only the exponent needs to be an int, that mantissa is a BigInteger so your Mersenne prime can be calculated by a BigInteger object ;)No bug ever had to calculate its fitnessfunction.
 07052011, 01:15 PM #8
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 07052011, 05:30 PM #9Member
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I've tried with and without longs neither way seemed to make a difference. I just stuck it in its own lil class and ran it like such
Java Code:public static void main(String[] args) { System.out.println(1509786213^3738585502L); }
 07052011, 05:37 PM #10
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I have the stamina of a seal; I lie on the beach instead of running on it.
 07052011, 05:38 PM #11Member
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So how are others getting the correct negative result?
 07052011, 05:41 PM #12
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 07052011, 05:45 PM #13Member
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Using them as literals it wont even compile, because the second number is too large. But you gave me enough insight to understand whats happening. I ended up casting the result back to an int and got the correct number. I've been in JS so long that I have to get reacquainted with strong typing. Thanks.
 07052011, 05:54 PM #14
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So now you did this:
Java Code:System.out.println((int)(1509786213^3738585502L));
kind regards,
JosI have the stamina of a seal; I lie on the beach instead of running on it.
 07052011, 06:16 PM #15Member
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Okay, I'm really sorry to keep bugging about this but I hit another problem, 2027172869^421330478. The result I'm looking for is 2654418389, but Java gives me 1640548907. I toyed around with int vs long and couldn't seem to get it working.
 07052011, 06:38 PM #16
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Print out those values in binary; the classes Integer and Long have method for it; also print out the binary form of the result and see.
kind regards,
JosI have the stamina of a seal; I lie on the beach instead of running on it.
 07052011, 07:03 PM #17Member
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I understand that the results are the same in binary, but how can I get Java to handle it properly, I think what youre tryin to get me to see is that its treating the result as an int when it needs to be a long but casting doesnt work since it wont just add in the extra bits.
 07052011, 07:59 PM #18
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Ok, subtract the result you're expecting from the result you're getting and see the result (all in int arithmetic). Also read about sign extension.
kind regards,
JosI have the stamina of a seal; I lie on the beach instead of running on it.
 07052011, 11:19 PM #19Member
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I got everything sorted. Thanks for all the help
 07062011, 08:11 AM #20
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