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java reading an unsigned int from file (into an int) and showing me the value as negative

Posted on 2014-09-03
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Last Modified: 2014-09-11
Hi Experts,

I'm reading an int from a stream in java and I know what I'm reading is an unsigned int, and obviously it's a big number because I get the negative sign on it (representation is negative because the negative bit is set).

I would like to know what the int value of -1083351007 is as an unsigned int?

Thanks,
Mike
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Question by:thready
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by:pepr
pepr earned 200 total points
ID: 40302114
I am not good in Java, but as far as I know, there is no unsigned integer there. You need to declare the variable as long (or the class Long wrapper).
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Neil Russell earned 100 total points
ID: 40302120
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by:pepr
pepr earned 200 total points
ID: 40302130
If you know you need to get only four bytes from the stream, you may need to read it as four bytes, detect the endianness, and compose the long value out of those four bytes.
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by:Jan Louwerens
Jan Louwerens earned 100 total points
ID: 40302136
It look like it's overflowing as an int value. Try readind it as a long value.

To convert that number into it's unsigned equivalent:
      int intValue = -1083351007;
      long longValue = Long.valueOf(intValue & 0xFFFFFFFFl);

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by:thready
ID: 40302150
all good answers, thanks everyone- I'm on the right track.  Although it is overflowing, all the data is in my variable as expected.  I will be back soon with points!  :)

The conversion to 3211616289 made me very happy  :o)
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by:zzynx
zzynx earned 100 total points
ID: 40302815
And if you know the insides
(
  - the maximum number that fits in an int is Integer.MAX_VALUE
  - a negative int is in fact a number that is too big to fit in an int
  - a negative int is Integer.MAX_VALUE plus the part that doesn't fit, being the number minus Integer.MAX_VALUE
)
here's yet another way to do it:

long longValue2 = (long)Integer.MAX_VALUE + (long)(intValue - Integer.MAX_VALUE);
System.out.println(longValue2);  // this is printing out 3211616289
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Author Closing Comment

by:thready
ID: 40316107
Thanks everyone, sorry for the late reply!
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Expert Comment

by:zzynx
ID: 40316354
You're welcome.
Thanx 4 axxepting
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