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libstdc++: Use fast_float for long double if it uses binary64 format

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We can use the new from_chars implementation when long double and double
have the same representation.

libstdc++-v3/ChangeLog:

	* src/c++17/floating_from_chars.cc (USE_STRTOD_FOR_FROM_CHARS):
	Define macro for case where std::from_chars is implemented in
	terms of strtod, strtof or strtold.
	(buffer_resource, valid_fmt, find_end_of_float, pattern)
	(from_chars_impl, make_result, reserve_string): Do not define
	unless USE_STRTOD_FOR_FROM_CHARS is defined.
	(from_chars): Define when at least one of USE_LIB_FAST_FLOAT and
	USE_STRTOD_FOR_FROM_CHARS is defined, instead of
	_GLIBCXX_HAVE_USELOCALE. Use fast_float for long double when it
	is binary64.
This commit is contained in:
Jonathan Wakely 2022-01-21 15:33:13 +00:00
parent 084680db9a
commit 416b6fc748
1 changed files with 32 additions and 6 deletions
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38
libstdc++-v3/src/c++17/floating_from_chars.cc
View file

@ -46,6 +46,13 @@
# include <xlocale.h>
#endif
#if _GLIBCXX_HAVE_USELOCALE
// FIXME: This should be reimplemented so it doesn't use strtod and newlocale.
// That will avoid the need for any memory allocation, meaning that the
// non-conforming errc::not_enough_memory result cannot happen.
# define USE_STRTOD_FOR_FROM_CHARS 1
#endif
#ifdef _GLIBCXX_LONG_DOUBLE_ALT128_COMPAT
#ifndef __LONG_DOUBLE_IBM128__
#error "floating_from_chars.cc must be compiled with -mabi=ibmlongdouble"
@ -56,6 +63,9 @@ extern "C" __ieee128 __strtoieee128(const char*, char**);
#if _GLIBCXX_FLOAT_IS_IEEE_BINARY32 && _GLIBCXX_DOUBLE_IS_IEEE_BINARY64
# define USE_LIB_FAST_FLOAT 1
# if __LDBL_MANT_DIG__ == __DBL_MANT_DIG__
# undef USE_STRTOD_FOR_FROM_CHARS
# endif
#endif
#if USE_LIB_FAST_FLOAT
@ -66,13 +76,13 @@ namespace
} // anon namespace
#endif
#if _GLIBCXX_HAVE_USELOCALE
namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION
namespace
{
#if USE_STRTOD_FOR_FROM_CHARS
// A memory resource with a static buffer that can be used for small
// allocations. At most one allocation using the freestore can be done
// if the static buffer is insufficient. The callers below only require
@ -409,6 +419,7 @@ namespace
return true;
}
#endif
#endif // USE_STRTOD_FOR_FROM_CHARS
#if _GLIBCXX_FLOAT_IS_IEEE_BINARY32 && _GLIBCXX_DOUBLE_IS_IEEE_BINARY64
// If the given ASCII character represents a hexit, return that hexit.
@ -771,13 +782,11 @@ namespace
return {first, errc{}};
}
#endif
#endif // _GLIBCXX_FLOAT_IS_IEEE_BINARY32 && _GLIBCXX_DOUBLE_IS_IEEE_BINARY64
} // namespace
// FIXME: This should be reimplemented so it doesn't use strtod and newlocale.
// That will avoid the need for any memory allocation, meaning that the
// non-conforming errc::not_enough_memory result cannot happen.
#if USE_LIB_FAST_FLOAT || USE_STRTOD_FOR_FROM_CHARS
from_chars_result
from_chars(const char* first, const char* last, float& value,
@ -855,6 +864,21 @@ from_chars_result
from_chars(const char* first, const char* last, long double& value,
chars_format fmt) noexcept
{
#if _GLIBCXX_FLOAT_IS_IEEE_BINARY32 && _GLIBCXX_DOUBLE_IS_IEEE_BINARY64 \
&& ! USE_STRTOD_FOR_FROM_CHARS
double dbl_value;
from_chars_result result;
if (fmt == chars_format::hex)
result = __floating_from_chars_hex(first, last, dbl_value);
else
{
static_assert(USE_LIB_FAST_FLOAT);
result = fast_float::from_chars(first, last, dbl_value, fmt);
}
if (result.ec == errc{})
value = dbl_value;
return result;
#else
errc ec = errc::invalid_argument;
#if _GLIBCXX_USE_CXX11_ABI
buffer_resource mr;
@ -875,6 +899,7 @@ from_chars(const char* first, const char* last, long double& value,
fmt = chars_format{};
}
return make_result(first, len, fmt, ec);
#endif
}
#ifdef _GLIBCXX_LONG_DOUBLE_COMPAT
@ -909,6 +934,7 @@ from_chars(const char* first, const char* last, __ieee128& value,
}
#endif
#endif // USE_LIB_FAST_FLOAT || USE_STRTOD_FOR_FROM_CHARS
_GLIBCXX_END_NAMESPACE_VERSION
} // namespace std
#endif // _GLIBCXX_HAVE_USELOCALE