[Koha] Barcodes with checkdigit

Hello, We are migrating to Koha from another system and so we already have barcodes on the books from that previous installation. But, the barcodes have a checkdigit at the end (probably not uncommon). When we export the current holdings from the old system, it only exports the "item" part of the barcode, not the location prefix or the checkdigit. I can easily add the prefix to each record before importing into Koha but the checkdigit is based on some unknown algorithm. I would like to avoid having to manually modify thousands of entries or even scan every barcode label and match it with the exported value. Any ideas? There must be someone who has faced the same problems (I hope). Thanks in advance, Dana Huff