How do you round a floating point number in Perl?

by

Output of perldoc -q round

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.

More Related Contents:

  1. Failing to install MIME::Base64 using cpan [closed]
  2. Declaring a 2D coordinate in Perl / C / C++ [closed]
  3. Why can’t Perl find my file that is in ClearCase?
  4. Difference of Two Arrays Using Perl
  5. round() doesn’t seem to be rounding properly
  6. How can I output UTF-8 from Perl?
  7. Get decimal portion of a number with JavaScript
  8. What’s the difference between a hash and hash reference in Perl?
  9. Multiline search replace with Perl
  10. How do I “use” a Perl module in a directory not in @INC?
  11. How can I process options using Perl in -n or -p mode?
  12. How can I hook into Perl’s print?
  13. How can I combine hashes in Perl?
  14. Why do my Perl tests fail with use encoding ‘utf8’?
  15. What is the difference between my and local in Perl?
  16. Why does my Perl script exit with 137?
  17. Perl read line by line
  18. What is the difference between Perl’s ( or, and ) and ( ||, && ) short-circuit operators?
  19. How do I change, delete, or insert a line in a file, or append to the beginning of a file in Perl?
  20. How can I install a specific version of a set of Perl modules?
  21. Obtain a switch/case behaviour in Perl 5
  22. How do I extract the domain out of an URL?
  23. Why does $foo->{bar} autovivify but %$foo doesn’t?
  24. What should I use for a Perl script’s shebang line?
  25. How can I find memory leaks in long-running Perl program?
  26. Why do Perl variables need to start with $, %,@ (sigils)?
  27. Print lines from one file that are not contained in another file
  28. Perl DBD::Oracle Module installation
  29. Explain the deviousness of the Perl “preamble”
  30. Why doesn’t Perl’s each() iterate through the entire hash the second time?

Leave a Comment