That really depends upon what format (within Perl), you are getting them in? Eg. Pure binary bytes; hex encoded etc.

And whether you're running a 64-bit integer capable version of Perl? Eg. Some 32-bit builds and all 64-bit builds will support the Q and q unpack formats specifically for handling this.

If you're using a 32-bit perl without 64-bit integers, then you can unpack the values as two 32-bit integers and then multiply them out to obtain an up to 53-bit integer value stored in a 64-bit real, which covers many uses. See Re: Hexadecimal to binary for one example of handling 128-bit values.

With a clearer description--and preferably a couple of samples--you'll get better responses.