Beefy Boxes and Bandwidth Generously Provided by pair Networks
Clear questions and runnable code
get the best and fastest answer

comment on

( #3333=superdoc: print w/replies, xml ) Need Help??

Most of the complication is in place to reduce file reading to a bare minimum. Say you have two 1 Gbyte files. The size is exactly the same, but the files are very different. I wouldn't want to read and digest both files to understand they are different, when it's enough to read a few bytes in the same position. My program deals rather well with these cases. It starts by reading a small chunk from all files of the same size and uses that chunk as key to partition the group of files. If any subset contains more than one file, then read another chunk starting from another (preferably far) position and iterate.

It's more or less like the naif "real life" way of comparing things. If you have two books with a blank cover, to check if they are different you first compare the size. If it's the same, you open the same page from both and check if they differ. Only if the books are the same you need to keep on reading until the end.

Moreover, by using byte by byte comparison instead of hashing, you don't even risk false positives. As small as the risk may be, it will most surely happen for your presentation due tomorrow.

Package Finder::Looper takes care of the iteration. Each call to $looper->next returns a new pair ( start, length ) within a given range, so that consecutive calls sample from different parts of the file. That's the "interlaced" part (which I should maybe have called "interleaved", but hey! this side of the world it's not the best time for choosing names in foreign languages).

Having said this, the program probably needs some tweaking to better exploit filesystem/buffering/head-positioning optimizations.


Antonio Bellezza

The stupider the astronaut, the easier it is to win the trip to Vega - A. Tucket

In reply to Re: •Re: Interlaced duplicate file finder by abell
in thread Interlaced duplicate file finder by abell

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

  • 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 or How to display code and escape characters are good places to start.
Log In?

What's my password?
Create A New User
Domain Nodelet?
and the web crawler heard nothing...

How do I use this? | Other CB clients
Other Users?
Others romping around the Monastery: (6)
As of 2022-05-23 20:22 GMT
Find Nodes?
    Voting Booth?
    Do you prefer to work remotely?

    Results (82 votes). Check out past polls.