Oh Dispensers of Wisdom, please come to my aid

Using the neat Win32::TieRegistry module I'm reading stuff from the Windows registry. The data gets written to a file, which is later read and processed. I'm having trouble with bit-twiddling after reading the data file, because of my limited understanding of pack, unpack and perl's internal data representation. I'm just missing something here -- possibly a piece of grey matter.

We're using ActiveState perl: "This is perl, version 5.005_03 built for MSWin32-x86-object" (but will probably be moving to a newer version soon.)

For REG_DWORD items read by Win32::TieRegistry's GetValue, the value is read thus: 

    my ( $value, $type ) = $key->GetValue( "$_" );
    # ---- format the value as text
    if ( $type == 4 )    # reg_dword
    {
        $value = hex( $value )
    }

[download]
So for a reg_dword value 0x00500000 in the registry, the string 5242880 is written to file.

Later I want to test and set bits in the value against a mask, so presumably it needs to be packed back into four bytes. Unfortunately none of my attempts to do this work, and I can't figure out how to "see" how perl is storing the data. Please can someone who has seen the light tell me how?

maybe something like this: 


    $dword  = pack <somehow> ( $value );   # eg $value = 5242880 dec

    $mask   = pack <somehow> ( 4194304 );  # 0x00400000
    $flags  = pack <somehow> ( 1048576 );  # 0x00100000

    $testdw = $dword & $mask;
    $newdw  = $dword | $flags;
    $newval = hex ( $newdw );   # gets written to file

[download]
Many thanks

In reply to how to pack bits, flags and masks by anadem

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