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Incorrect string formatting for numbers larger than Int64.max (2^63 - 1) #113
Description
Activity
import BigInt extension Foundation.FormatStyle where Self == IntegerFormatStyle<BigUInt> { static var number: IntegerFormatStyle<BigUInt> { IntegerFormatStyle<BigUInt>() } } var hmm: BigUInt = 9_223_372_036_854_775_807 while true { let formatted = hmm.formatted(.number.locale(Locale(identifier: "en_US_POSIX"))) if BigUInt(formatted) != hmm { print("Broke at \(hmm.description) - \(formatted).") break } hmm += 1 }
Note that in the above example I added a
numberstatic member toFormatStylefor convenience (as the built-in overloads ofnumberare only for the Swift built-in numeric types), but that's not germane to the problem. If you delete that extension you can't use.numberanymore, but can still see the problem with other standard format style conveniences e.g.hmm.formatted(.currency(code: "usd")).Also,
IntegerFormatStylebreaks with UInt64 at the same point. So this looks like a bug in the Swift standard library, in which case this GitHub issue is more of an FYI, I suppose. Maybe there's some way to work around the issue, e.g. provide aFormatStyleimplementation specifically forBigInt/BigUInt?
description(perCustomStringConvertible) seems to work fine, but of course doesn't produce localised outputs (as expected per its purpose). I want localised outputs, which is normally (for the built-in numeric types) done via theformatted(…)methods. These do exist onBigIntandBigUInt, but produce erroneous results at 2^63 and higher (9,223,372,036,854,775,808).e.g. 2^63 renders as "9,223,372,036,854,775,807" (which is 2^63 - 1, which happens to be
Int64.max).e.g. 1e25 renders as "9,999,999,999,999,999,000,000,000".
It appears the formatting's precision is somehow limited to the first (highest-order)
Int64word, even though it does show the correct magnitude ("rounding" errors notwithstanding).