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Thread: Evaluating to negative zero

  1. #1
    Super Moderator helloworld922's Avatar
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    Default Evaluating to negative zero

    Don't know if anyone's tried this, but:

    System.out.println((0*3*Math.sin(4)));
    output:
    -0
    even if you set it to a double variable:
    double a = 0*3*Math.sin(4);
    System.out.println(a);
    output:
    -0
    if (a == 0)
    {
    System.out.println("-0 equals 0");
    }

    any thoughts on why this is?


  2. #2
    mmm.. coffee JavaPF's Avatar
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    Default Re: Evaluating to negative zero

    Hello helloworld922,

    What made you do this? What output would you be expecting?
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    Super Moderator helloworld922's Avatar
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    Default Re: Evaluating to negative zero

    I was testing my parser with fairly random expressions to see if it was correct. When this spit out -0, i did a few tests in java itself to see what java did.

    I expected it to be positive 0.

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    Default Re: Evaluating to negative zero

    Hmm... No idea!

    Math (Java Platform SE 6)
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    Senile Half-Wit Freaky Chris's Avatar
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    Default Re: Evaluating to negative zero

    Turns out Java has a bit of a problem. When you multiply any float / double by 0 you will always get the sign of the original double / float, rather than plain positive 0.

    Hence why 0*3*-0.75..... returns -0.

    Chris
    chris[at]javaprogrammingforums[dot]com

    Prifysgol Bangor University, North Wales

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    Super Moderator helloworld922's Avatar
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    Default Re: Evaluating to negative zero

    well, i guess at least they bothered to make -0 = 0

  7. #7
    Senile Half-Wit Freaky Chris's Avatar
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    Default Re: Evaluating to negative zero

    indeed lol
    chris[at]javaprogrammingforums[dot]com

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