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Use the Grisu2 algorithm for formatting 'float's and 'double's

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abolz 2018-01-15 20:58:02 +01:00
parent 332f352033
commit 9f7c2c04c8
1 changed files with 24 additions and 1 deletions
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25
develop/detail/serializer.hpp
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@ -14,6 +14,7 @@
#include <string> // string #include <string> // string
#include <type_traits> // is_same #include <type_traits> // is_same
#include "detail/conversions/to_chars.hpp"
#include "detail/macro_scope.hpp" #include "detail/macro_scope.hpp"
#include "detail/meta.hpp" #include "detail/meta.hpp"
#include "detail/parsing/output_adapters.hpp" #include "detail/parsing/output_adapters.hpp"
@ -636,12 +637,34 @@ class serializer
void dump_float(number_float_t x) void dump_float(number_float_t x)
{ {
// NaN / inf // NaN / inf
if (not std::isfinite(x) or std::isnan(x)) if (not std::isfinite(x))
{ {
o->write_characters("null", 4); o->write_characters("null", 4);
return; return;
} }
// If number_float_t is an IEEE-754 single or double precision number,
// use the Grisu2 algorithm to produce short numbers which are guaranteed
// to round-trip, using strtof and strtod, resp.
//
// NB: The test below works if <long double> == <double>.
static constexpr bool is_ieee_single_or_double
= (std::numeric_limits<number_float_t>::is_iec559 and std::numeric_limits<number_float_t>::digits == 24 and std::numeric_limits<number_float_t>::max_exponent == 128) or
(std::numeric_limits<number_float_t>::is_iec559 and std::numeric_limits<number_float_t>::digits == 53 and std::numeric_limits<number_float_t>::max_exponent == 1024);
dump_float(x, std::integral_constant<bool, is_ieee_single_or_double>());
}
void dump_float(number_float_t x, std::true_type /*is_ieee_single_or_double*/)
{
char* begin = number_buffer.data();
char* end = ::nlohmann::detail::to_chars(begin, begin + number_buffer.size(), x);
o->write_characters(begin, static_cast<size_t>(end - begin));
}
void dump_float(number_float_t x, std::false_type /*is_ieee_single_or_double*/)
{
// get number of digits for a text -> float -> text round-trip // get number of digits for a text -> float -> text round-trip
static constexpr auto d = std::numeric_limits<number_float_t>::digits10; static constexpr auto d = std::numeric_limits<number_float_t>::digits10;