Beefy Boxes and Bandwidth Generously Provided by pair Networks
go ahead... be a heretic
 
PerlMonks  

comment on

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

I have a binary file (think ELF or Windows PE) that includes fields that may be long (32 bit) or quad (64) bit and little or big endien depending on the specific file. The script may be running on a big or little endian machine with a Perl built for 32 or 64 bits. I want to unpack the fields for later use that will include display using printf and file operations using read and seek so I need to convert from file representation to the running Perl's native representation for those fields. The following sample code does that, but the pack 'L2' ...; unpack 'Q' feels a bit clunky. Can it be tidied up?

use warnings; use strict; use Config; use Fcntl; printf "Perl $^V %s ivsize %d byteorder %d\n", $Config{archname}, $Config{ivsize}, $Config{byteorder}; # Generate a "binary file" with a string of bytes likely to show up is +sues in # decoding my $binary = "\x91\x34\x33\x90\x81\x32\x31\x80"; for my $fileLE (0, 1) { my $fromFile = $fileLE ? 'V4' : 'N4'; open my $inFH, '<:raw', \$binary; read $inFH, my $raw1, 4; read $inFH, my $raw2, 4; my $long1 = unpack $fromFile, $raw1; my $long2 = unpack $fromFile, $raw2; my $packed = pack "L2", $fileLE ? ($long1, $long2) : ($long2, $lon +g1); my $longlong = unpack 'Q', $packed; printf "%s: %016x\n", ($fileLE ? "LE" : "BE"), $longlong; }

A 32 bit Windows build prints:

Perl v5.32.0 MSWin32-x86-multi-thread-64int ivsize 8 byteorder 1234567 +8 BE: 9134339081323180 LE: 8031328190333491

A nice sanity check would be to run the code on a big endian system and see that the numbers generated are the same. Of course the long long processing will come unstuck where ivsize < 8.

Optimising for fewest key strokes only makes sense transmitting to Pluto or beyond

In reply to Unpacking byte stream long/quad little/big endian fields by GrandFather

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, 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, 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.
  • Log In?
    Username:
    Password:

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

    How do I use this? | Other CB clients
    Other Users?
    Others scrutinizing the Monastery: (2)
    As of 2021-04-23 04:26 GMT
    Sections?
    Information?
    Find Nodes?
    Leftovers?
      Voting Booth?

      No recent polls found

      Notices?