Unless you have esoteric hardware your platform probably supports IEEE754 floats.

The most probable cause of incompatibility is that the MS platform uses a little-endian byte order and your other platform uses a big-endian byte order. Try the following code on both platforms and compare the output: 

    my $num = 1.2345;

    print join(" ", map { sprintf "0x%02x", $_ } 
                    unpack("C*", pack "f", $num)), "\n";

[download]
If one is the reverse of the other you can use the following to unpack the float:     my $num = unpack "f", reverse $packed_num;

One other thing to look out for is that the floating point number might be packed as a 8-byte double and not as a 4-byte float.

Finally, as a *last* resort (because I think your problem is elsewhere) here is a function to portably unpack a 4-byte IEEE754 float in little-endian order. This is a port of a C function by Steve Summit from the book "C Unleashed": 

    use POSIX 'ldexp';

    sub unpack_f_ieee754 {

        my @buf = unpack "C4", $_[0];
        my $mant;
        my $num;

        $mant  =  $buf[0];
        $mant |=  $buf[1]         << 8;
        $mant |= ($buf[2] & 0x7f) << 16;


        my $exp  = (($buf[3] & 0x7f) << 1) | (($buf[2] >> 7) & 0x01);
        my $sign = $buf[3] & 0x80;


        if ($exp == 0) {
            $num = ldexp($mant, -126 -23);
        }
        else {
            # restore implicit leading
            $mant |= 1 << 23;
            $num   = ldexp($mant, $exp -127 -23);
        }

        $num = -$num if $sign;

        return $num;
    }

[download]

--
John.

In reply to Re: Extracting IEEE 754 floating point numbers by jmcnamara
in thread Extracting IEEE 754 floating point numbers by physgreg

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