http://qs321.pair.com?node_id=656344

andreas1234567 has asked for the wisdom of the Perl Monks concerning the following question:

Monks,

I have difficulties converting data on a binary format to decimal numbers related to this node. I suspect the number are encoded using a float. I'm able to see what the results should be using a third-party tool.

The number should perform as follows:

What kind of conversion of unpack trickery am I in search for?

A hexdump of the source file is available on my pad (relax it's only 192 bytes).

Update: It seems like this does the trick (updated as shown by Anonymous Monk): 

# read number: 8 bytes, return decimal value
sub getnumber {
  my $buffer = undef;
  my $num = read($FH, $buffer, 8);
  return unpack 'd*', reverse $buffer;
}

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Update: pfaut++ and Fletch++ for good advice to stubborn monk.
--
Andreas

Replies are listed 'Best First'.
Re: Binary to decimal conversion
by Anonymous Monk on Dec 11, 2007 at 10:19 UTC
    Too much joining :)
    return unpack 'd*', reverse $buffer;

    [download]
[reply]
[d/l]
      Hmm.. I'm surprised to see it works to reverse a scalar like that. read's 2nd argument is a SCALAR, and reverse's single argument is a LIST. What is it I do not understand?
      --
      Andreas
[reply]

        From reverse

        reverse LIST
      In list context, returns a list value consisting of the ele-
      ments of LIST in the opposite order.  In scalar context, con-
      catenates the elements of LIST and returns a string value with
      all characters in the opposite order.
        90% of every Perl application is already written. ⇒
        dragonchild
[reply]
Re: Binary to decimal conversion
by Anonymous Monk on Dec 11, 2007 at 09:24 UTC 
        // read number
    function readNumber(){
        $num = fread($this->buffer, 8);
        $r = "";
        for($byte = 7 ; $byte >= 0 ; $byte--) { // reverse the bytes
            $r .= $num[$byte];
        }
        $ret = unpack("dnum",$r);
        return $ret['num'];
    }

    [download]
[reply]
[d/l]
      That looks at lot like the lines 153-162 from here (direct link here): 
      153    // read number
154    function readNumber(){
155      $num = fread($this->buffer, 8);
156      $r = "";
157      for($byte = 7 ; $byte >= 0 ; $byte--) { // reverse the bytes
158        $r .= $num[$byte];
159      }
160      $ret = unpack("dnum",$r);
161      return $ret['num'];
162    }

      [download]
      And I believe that's PHP, not Perl. I'm thankful for the suggestion although still looking for the Perl equivalent of the above.
      --
      Andreas
[reply]
[d/l]
        Translate that to perl, its easy
[reply]

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