Floating-point formatting #915
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…loating-point conversion This is an attempt to fix #360. The algorithm produces decimal representations which are guaranteed to roundtrip and in ~99.8% actually produces the shortest possible representation. So this is a nice compromise between using a precision of digits10 and max_digits10. Note 1: The implementation only works for IEEE single/double precision numbers. So the old implementation is kept for compatibility with non-IEEE implementations and 'long double'. Note 2: If number_float_t is 'float', not all serialized numbers can be recovered using strtod (strtof works, though). (There is exactly one such number and the result is off by 1 ulp.) This can be avoided by changing the implementation (the fix is trivial), but then the resulting decimal numbers are not exactly short.
nlohmann
reviewed
Jan 21, 2018
| o->write_characters(begin, static_cast<size_t>(end - begin)); | ||
| } | ||
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| void dump_float(number_float_t x, std::false_type /*is_ieee_single_or_double*/) |
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Just out of curiosity: why do we still need the snprintf approach?
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Because the implementation only works for IEEE single and double precision.
It should work in case long double is an alias for double, though.
| @@ -7079,14 +8108,36 @@ class serializer | |||
| void dump_float(number_float_t x) | |||
| { | |||
| // NaN / inf | |||
| if (not std::isfinite(x) or std::isnan(x)) | |||
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Its actually not ignored: the isnan test is just redundant. isfinite return false for NaN
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Thanks a lot! |
This was referenced Jan 21, 2018
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Try to fix #360. printf doesn't have a "to shortest" mode and std::to_chars is not available yet. Use the Grisu2 algorithm for floating-point formatting which is a nice compromise between using printf with a precision of digits10 and max_digits10, i.e. the resulting decimal representation is guaranteed to round-trip and is almost always the shortest such representation.