* You should be using binmode on your input handle.

In the real program this is in a subroutine which gets pre-opened handles passed in; I just added a quick open at the top here to have a runnable snippet.

* ($check_value & 0x7fffffff) << 1 might be safer (more portable) than ($check_value << 1) & 0xffffffff

It more clearly shows what it's actually trying to do as well I think. Thanks.

* The following is faster (but nowhere near as fast as C would be): 
 $check_value ^= unpack('L', $_); 
 $check_value = ( ($check_value & 0x7fffffff) << 1 )
              | ( $check_value >> 31 );

[download]

As shown in my reply to BrowserUK below (which I'll post in a little bit), this cut my time from 1:38 to 1:26, or about a 12% improvement.

* Using C doesn't require shelling out. perlxstut or Inline::C will allow you to access C code from perl.

I looked at Inline::C, but that appears to require a compiler to be available at runtime, which isn't guaranteed. Still it might be worth doing a "use it if it's there" type thing.

So in the end I took BrowserUK's C code below and did all the magic xs invocations to get an .so; I'm including that inside an eval, so if the .so is not there it'll fall back to the slow perl implementation.

In reply to Re^2: Improving performance of checksum calculation by Crackers2
in thread Improving performance of checksum calculation by Crackers2

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.