I take it back!

Having looked in more detail at the specification this morning, I see why you're having problems working out how to do this.

This is one of those really nasty pieces of mainframe/COBOL-esque encoding, that requires BCD math on a fixed length BCD field. (COBOL: PIC 9(13) COMP).

Perl's pack & unpack don't have anything to handle this directly, and even on a 64-bit machine, integer math simply isn't capable of handling 13-byte numbers.

One way might be to drop into Inline::C and inline assembler (or Inline::Asm ) and use the vestigal BCD opcodes. (Though MS 64-bit compilers don't support inline assembler.)

There are also some weird x64 opcodes that treat an 80-bit floating point register as a 17 digit BCD value that might be pressed into service for this.

Perhaps the easiest and most portable way would be to use Math::BigInt to do the math; as_hex() to get it out of BigInt format; and then pack 'H26' to creat the binary string.

Or download the USPS libraries and link them from XS.

I think that the BigInt method would be easiest. Let us know if you need help with that?