The problem is, that most languages have no native support other than 32 or 64 bit floats and some representations on the wire don't either. And most underlying processors don't have arbitrary precision support either.
So either you choose speed and sacrifice precision, or you choose precision and sacrifice speed. The architecture might not support arbitrary precision but most languages have a bignum/bigdecimal library that will do it more slowly. It might be necessary to marshal or store those values in databases or over the wire in whatever hacky way necessary (e.g. encapsulating values in a string).