Since you are dealing only with small numbers you could use Fox' builtin currency type, which is a 64-bit signed integer scaled by 1/10000. This gives you 18.96 digits of precision - you just have to scale your input values down and remove the decimal separator after transforming the result.

We use this for calculating the checksums over bank instution numbers and banking account numbers when we generate money transfer data (these 17-digit checksums are required for the DTA format here in Germany). In this case the 'input transformation' is just

val("$" + stuff(padl(alltrim(m.cNum), 17, "0"), 14, 0, set("POINT")))

where cNum is an account number, checksum string or whatever. The constants 17 and 14 (= 17 - 4 + 1) need to be adjusted if your input strings can be longer, because otherwise PADL() would silently trim any excess length and even if it didn't then STUFF() would put the decimal separator in the wrong place.