Dear monks,

I came to problem, when I wanted convert python code to perl. It is about calculating custom hash of file, in general it should do following: filesize + 64bit chksum of the first and last 64k (even if they overlap because the file is smaller than 128k) Source codes for other languages are here I am not good in bits operation, pack, unpack and uint64...but I did try, and here is what I came up with: 
#!/usr/bin/perl -w
use strict;

die "need file as parameter" unless my $file = $ARGV[0];

open(my $fh, $file) or die "Can't open file $file: $!";
die "File $file is too small!" if -s $file < 65536;

my $hashstring = -s $file;

#calculate first 64kb
for(1 .. 65536/8) {
    read($fh, my $byte, 4);
    my $ll = unpack("LL", $byte);
    #here is missing code
}

#calculate last 64kb
seek $fh, -65536, 2;
for(1 .. 65536/8) {
    read($fh, my $byte, 4);
    my $ll = unpack("LL", $byte);
    #here is missing code
}
close($fh);

printf("Hash of $file is: %016x", $hashstring);

[download]
Please, help me, so I will get the same hash using perl. Thank you monkers!

In reply to Creating custom hash of file by 2ge

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.