Here are two variations. The first uses sprintf to do the zero padding. The second uses oct to convert the binary string to decimal (for perl >= 5.6).

For clarity I've omitted the $$OffsetRef part. Using proper bitmasks and the bitwise operators would probably be faster, see perlop.

    sub ReadBits2
    {
        my $bitstring  = @_[0];
        my $offset     = @_[1];
        my $length     = @_[2];

        return unpack  "N",
               pack    "B*",
               sprintf "%032s",
               substr  $bitstring, $offset, $length;
    }



    sub ReadBits3
    {
        return oct b . substr @_[0], @_[1], @_[2];
    }
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--
John.