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This is an excerpt from the latest version perlfaq4.pod, which
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4.4: Does Perl have a round() function? What about ceil() and floor()? Trig functions?

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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