As you know, a tiny error log($size) / log(2) could lead to a big error in the result. Perl Differences in the underlying C libraries and hardware can result in those tiny differences on other systems even if they don't exist on your own.

I suppose the error coming from floating point arithmetic can bite me only in the case when $size is a power of 2

You also need to check one less than powers of two for errors rounding up.

249 = 562949953421312 

$ perl -E'say int( log(562949953421309) / log(2) )'
48

$ perl -E'say int( log(562949953421310) / log(2) )'
49     XXX

$ perl -E'say int( log(562949953421311) / log(2) )'
49     XXX

$ perl -E'say int( log(562949953421312) / log(2) )'
49

$ perl -E'say int( log(562949953421313) / log(2) )'
49

[download]

(Problem found by accident)

In reply to Re: May I be bitten by floating point arithmetic in the following restricted case? by ikegami
in thread May I be bitten by floating point arithmetic in the following restricted case? by rubasov

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.