#### Do you have a question? Post it now! No Registration Necessary. Now with pictures!

**posted on**

- PerlFAQ Server

September 8, 2009, 4:00 pm

This is an excerpt from the latest version perlfaq4.pod, which

comes with the standard Perl distribution. These postings aim to

reduce the number of repeated questions as well as allow the community

to review and update the answers. The latest version of the complete

perlfaq is at http://faq.perl.org .

--------------------------------------------------------------------

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

alternation:

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.

--------------------------------------------------------------------

The perlfaq-workers, a group of volunteers, maintain the perlfaq. They

are not necessarily experts in every domain where Perl might show up,

so please include as much information as possible and relevant in any

corrections. The perlfaq-workers also don't have access to every

operating system or platform, so please include relevant details for

corrections to examples that do not work on particular platforms.

Working code is greatly appreciated.

If you'd like to help maintain the perlfaq, see the details in

perlfaq.pod.

#### Site Timeline

- » Perl regex expression to return values
- — Next thread in » PERL Discussions

- » Need expert help matching a line
- — Previous thread in » PERL Discussions

- » s suffix question
- — Newest thread in » PERL Discussions

- » Adblock Testscript problem
- — The site's Newest Thread. Posted in » HTML Markup Language