FAQ 4.4 Does Perl have a round() function? What about ceil() and floor()? Trig functions...

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4.4: Does Perl have a round() function?  What about ceil() and floor()?  Trig

    Remember that "int()" merely truncates toward 0. For rounding to a
    certain number of digits, "sprintf()" or "printf()" is usually the
    easiest route.

            printf("%.3f", 3.1415926535);   # prints 3.142

    The "POSIX" module (part of the standard Perl distribution) implements
    "ceil()", "floor()", and a number of other mathematical and
    trigonometric functions.

            use POSIX;
            $ceil   = ceil(3.5);   # 4
            $floor  = floor(3.5);  # 3

    In 5.000 to 5.003 perls, trigonometry was done in the "Math::Complex"
    module. With 5.004, the "Math::Trig" module (part of the standard Perl
    distribution) implements the trigonometric functions. Internally it uses
    the "Math::Complex" module and some functions can break out from the
    real axis into the complex plane, for example the inverse sine of 2.

    Rounding in financial applications can have serious implications, and
    the rounding method used should be specified precisely. In these cases,
    it probably pays not to trust whichever system rounding is being used by
    Perl, but to instead implement the rounding function you need yourself.

    To see why, notice how you'll still have an issue on half-way-point

            for ($i = 0; $i < 1.01; $i += 0.05) { printf "%.1f ",$i}

            0.0 0.1 0.1 0.2 0.2 0.2 0.3 0.3 0.4 0.4 0.5 0.5 0.6 0.7 0.7
            0.8 0.8 0.9 0.9 1.0 1.0

    Don't blame Perl. It's the same as in C. IEEE says we have to do this.
    Perl numbers whose absolute values are integers under 2**31 (on 32 bit
    machines) will work pretty much like mathematical integers. Other
    numbers are not guaranteed.


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