Should your code not be: 

perl -e 'for my $i (1..63) {if(int(log(2**($i-1))/log(2)) != $i-1) {pr
+int "$i\n"}}'

[download]

which gives no output for me.

UPDATE: Apologies, I think I get it now, the leading one of 2^i - 1 should be in the same place as the leading one for 2^(i-1) which is what you are testing.

My next thought was to use length(sprintf("%b",$x)) but that does not work either:

for my $i (1..63) {
    if(length(sprintf("%b",2**$i-1)) != length(sprintf("%b",2**($i-1))
+)) {
    print"$i\n";
    printf("%b\n",2**($i-1));
    printf("%b\n",(2**$i)-1);
    }
}

[download]

In reply to Re: reliable get position of leftmost bit in large integers by hdb
in thread reliable get position of leftmost bit in large integers by wollmers

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.