A way to achieve perfect round-tripping was proposed back in 1990, by Steele and White (and likely they are not the first ones who came up with a similar idea). I guess their proposal probably wasn't extremely popular at least until 2000's, compared to more classical `printf`-like rounding methods, but it seems many languages and platforms these days do provide such round-tripping formatting algorithms as the default option. So, I guess nowadays roundtripping isn't that hard, unless people do something sophisticated without really understanding what they're doing.