I came up with the following, which works for my use-case ...

Note that the floating point value 1/3 is not the same as the rational value 1/3, and while your subroutine works as you want for your use case, it won't work correctly for (eg) cube_root( -91197 ** 3 ), where it will return -91196.9999999999.
For general purposes, you therefore really need an implementation that performs cbrt(x), as opposed to pow(x, 1 / 3).
haukex has already shown that the excellent Math::Prime::Util::GMP module provides what you're after.
My own Math::MPFR module provides the same capability (courtesy of the mpfr C library):

C:\>perl -MMath::MPFR=":mpfr" -le "$op = Math::MPFR->new(-9117 ** 3); 
+Rmpfr_cbrt($op, $op, MPFR_RNDN); print $op;"
-9.117e3
[download]

or, the more general:

C:\>perl -MMath::MPFR=":mpfr" -le "$op = Math::MPFR->new(-9117 ** 3); 
+Rmpfr_rootn_ui($op, $op, 3, MPFR_RNDN); print $op;"
-9.117e3
[download]

Cheers,
Rob

---

---

• Are you posting in the right place? Check out Where do I post X? to know for sure.
• Posts may use any of the Perl Monks Approved HTML tags. Currently these include the following:

  <code> <a> <b> <big> <blockquote> <br /> <dd> <dl> <dt> <em> <font> <h1> <h2> <h3> <h4> <h5> <h6> <hr /> <i> <li> <nbsp> <ol> <p> <small> <strike> <strong> <sub> <sup> <table> <td> <th> <tr> <tt> <u> <ul>

• Snippets of code should be wrapped in <code> tags not <pre> tags. In fact, <pre> tags should generally be avoided. If they must be used, extreme care should be taken to ensure that their contents do not have long lines (<70 chars), in order to prevent horizontal scrolling (and possible janitor intervention).
• Want more info? How to link or How to display code and escape characters are good places to start.