float::from_str and NaN/inf/-inf

[grahame]

Should float::from_str do the following conversions?
"NaN" -> float::NaN
"inf" -> float::infinity
"-inf" -> float::neg_infinity

That'd match what float::to_str does (if my pull request #2164 is merged.)

If this sounds good I'll chuck a patch in.

[boggle]

It will be very good when this will be fixed. There are some additional points to be considered:

If I remember correctly, the floating point standard allows for both short ("inf") and long ("infinity") syntax.

Are you aware of the other float formatting related issues? I think there used to be a floating point literal parsing problem in rustc for very large literals (not fitting into 32 bits) that is related (can't find the issue right now).

Besides adding support for NaN and inf in from_str/to_str, I personally think rust should define a literal syntax for these, i.e. the compiler should support them directly.

[brson]

If this is standard behavior for converting from strings than I say go for it.

[boggle]

More things to check

• proper handling of +0.0 vs -0.0 vs 0.0
• hexadecimal notation for the mantissa for the lossless exchange of values

[boggle]

The last one is discusses in #1433. The real kicker would be if all this were supposed by the parser as literal syntax.

[brson]

Fixed by 6b5731e