Parse decimal real number to f64 without error

1

Hello i'm seeking for a way to store a string representation of a number. What i want is that if the number can be stored into a f64 without any data loss, use a f64 instead, e.g.

enum F64OrStr {
    F64(f64),
    Str(String),
}

There is actually parsing code in libcore, i know, but the existing code simply ignores non-significant errors, and there's no way to detect it. I can accept slower parsing, in exchange for always precise results, if out of range, just use the string variant.

Do you have any suggestions?

2

How strict are you about any data loss? Because e.g. "0.1" is impossible to represent in f64.

If storing a string is an option, maybe always just use the string?

Within std there's probably not much you can do. You could try if parsed_f64.to_string() == input_string, but this will give false negatives on slightly unusual notations.

1 Like
3

If you sometimes store things as strings that didn't necessarily need to be, is that ok? If so, you could use a simple heuristic like "14 sigfigs fit in an f64 for reasonable exponents".

2 Likes
4

Thank you for the suggestions, now i'm thinking about always using decimal64, maybe f64 just doesn't worth all these trouble...

I'll take a try to see if decimal*'s performance is good enough.

5

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