Be careful with JS numbers

Re:Be careful with JS numbers by martin-adams on Sunday January 13, 2013 @02:44PM (#5051622)

I got hit by JavaScript rounding on a project once. Funny thing is, IE8 was okay with it and Chrome was the one that caused issues.

Turns out that 1000000 * 8.2 = 8199999.999999999

Sometimes we learn the hard way. The bug was getting written into an XML document and pushed to an embedded device over HTTP which was expecting an int and caused the device to crash. We fixed both bugs.

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Re:Be careful with JS numbers by ricardobeat on Sunday January 13, 2013 @04:03PM (#5051852)

    // Scheme
    (print (* 1000000 8.2))
    > 8199999.999999999

    // Python
    >>> 1000000 * 8.2
    8199999.999999999

    //PHP
    > 1000000 * 8.2
    > 8199999.999999999

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Re:Be careful with JS numbers by ehsanu1 on Sunday January 13, 2013 @04:10PM (#5051866)

    # Ruby 1.8.7
    1.8.7 :022 > 1000000 * 8.2
     => 8200000.0 

    # Ruby 1.9.2
    1.9.2p320 :001 > 1000000 * 8.2
     => 8199999.999999999

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Re:Be careful with JS numbers by jabiko on Sunday January 13, 2013 @05:12PM (#5052102)

I can't reproduce the PHP example:

  $ uname -p
  x86_64
  $ php -v
  PHP 5.4.6-1ubuntu1 (cli) (built: Aug 22 2012 21:13:52)
  Copyright (c) 1997-2012 The PHP Group
  Zend Engine v2.4.0, Copyright (c) 1998-2012 Zend Technologies
  $ php -r 'var_dump(1000000 * 8.2);'
  float(8200000)
  $

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Re:Be careful with JS numbers by ricardobeat on Sunday January 13, 2013 @09:41PM (#5053028)

My fault, I think I copied from the wrong REPL.

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Re:Be careful with JS numbers by CamperBob2 on Sunday January 13, 2013 @04:34PM (#5051941)

C/C++:

   printf("%lf\n", 1000000 * 8.2);
   8200000.000000

Here, printf() is doing the necessary rounding to hide the fact that 8.2 isn't exactly representable. It's interesting that other languages don't do something similar when outputting a float to text.

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Re:Be careful with JS numbers by pindi on Sunday January 13, 2013 @05:36PM (#5052172)

They do, you just have to request it:

    //Python
    >>> repr(1000000 * 8.2)
    '8199999.999999999'
    >>> "%lf" % (1000000 * 8.2)
    '8200000.000000'

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