FAQ 4.2 Why is int() broken?

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4.2: Why is int() broken?

    Your "int()" is most probably working just fine. It's the numbers that
    aren't quite what you think.

    First, see the answer to "Why am I getting long decimals (eg,
    19.9499999999999) instead of the numbers I should be getting (eg,

    For example, this

            print int(0.6/0.2-2), "\n";

    will in most computers print 0, not 1, because even such simple numbers
    as 0.6 and 0.2 cannot be presented exactly by floating-point numbers.
    What you think in the above as 'three' is really more like


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Re: FAQ 4.2 Why is int() broken?

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Why subtract 2? This example works just as well without the subtraction:

        perl -e 'print int(0.6/0.2), "\n";'

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I don't like the phrase "even such simple numbers as 0.6 and 0.2". It
implies that these numbers are "simple" and that there is much less of a
chance that such "complicated" numbers as 952279704355844 or
0.845794282927275986594395362772047519683837890625 can be represented
exactly, when in fact they can. Also "by floating-point numbers" is
incorrect in its generality - they could be represented by decimal
floating-point numbers.

How about

    ... because 0.6 and 0.2 cannot be presented exactly by binary
    floating-point numbers because they are not multiples of a power of

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And that can be easily demonstrated by subtracting 3:

        perl -e 'print +(0.6/0.2) - 3, "\n";'


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