I've taken a look at Digest::Nilsimsa. It is a cool thing. However, I've found a problem. 
for my $d ( 30 .. 36 ) {
  my $this = $nil->text2digest( ( 'a' x $d ) . 'b' ) ;
  my $that = $nil->text2digest( ( 'a' x ( $d + 1 ) ) ) ;
  print nilcomp( $this , $that ) ;
  }

sub nilcomp {
  my $diff = 0 ;
  my $diff2 = 0 ;
  my @this = split /|/ , shift ;
  my @that = split /|/ , shift ;
  for my $a ( 0 .. scalar(@this)-1 ) {
    $diff++ if $this[$a] ne $that[$a] ;
    my $is = hex $this[$a] ;
    my $at = hex $that[$a] ;
    if ( $is != $at ) {
      $diff2 += abs $is - $at ;
      }
    }
  return ( join "" , @this) . qq(\n) .
         ( join "" , @that) . qq(\n) .
         $diff . qq( characters different\n) .
         ( abs $diff2 ) . qq( bits different\n\n);
  }

[download]
gives you 
000000000000900000010021000008105000080010000004000c400000000008
0000000000009000000000200000080040000000000000040008400000000000
8 characters different
25 bits different

000000000000900000010021000008105000080010000004000c400000000008
0000000000009000000000200000080040000000000000040008400000000000
8 characters different
25 bits different

000000000000900000010021000008105000080010000004000c400000000008
0000000000009000000000200000080040000000000000040008400000000000
8 characters different
25 bits different

000000000000900000010021000008105000080010000004000c400000000008
0000000000009000000000200000080040000000000000040008400000000000
8 characters different
25 bits different

000000000000900000010021000008105000080010000004000c400000000008
0000000000009000000000200000080040000000000000040008400000000000
8 characters different
25 bits different

0000000000009000000000200000080040000000000000040008400000000000
0000000000009000000000200000080040000000000000040008400000000000
0 characters different
0 bits different

0000000000009000000000200000080040000000000000040008400000000000
0000000000009000000000200000080040000000000000040008400000000000
0 characters different
0 bits different

[download]
If all I was trying to use this on were 35-character data sets, that'd be cool, but I'm trying to run this on whole web pages. I pull out all markup and whitespace, I'll still be in the headers by the time the 35th character rolled around. I love it in theory, but in practice, the data's too big for the module. So, I could do this:  $output =~ s[(.{35})][$nilsimsa->text2digest($1)]ge ; or something of the sort, but that seems ... goofy. But it does point out that taking length $output and comparing it to last time should indicate a small change, if they're only a small number of characters apart.

.sig goes here

In reply to Re^2: Quantitative Change instead of Boolean by titivillus
in thread Quantitative Change instead of Boolean by titivillus

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.