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libstdc++: Make std::from_chars always round to nearest

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Also fix the tests that fail on targets without uselocale.

libstdc++-v3/ChangeLog:

	* src/c++17/floating_from_chars.cc (from_chars_impl): Ensure
	that FE_NEAREST is used.
	* testsuite/20_util/from_chars/4.cc: Do not use if constexpr in
	a { target c++14 } test.
	[!_GLIBCXX_HAVE_USELOCALE]: Disable all tests.
	* testsuite/20_util/from_chars/5.cc [!_GLIBCXX_HAVE_USELOCALE]:
	Likewise.
	* testsuite/20_util/from_chars/6.cc: New test.
This commit is contained in:
Jonathan Wakely 2020-07-27 15:51:16 +01:00
parent 7355a9408b
commit 2251b4a542
4 changed files with 74 additions and 2 deletions
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12
libstdc++-v3/src/c++17/floating_from_chars.cc
View File

@ -30,6 +30,7 @@
#include <charconv>
#include <string>
#include <memory_resource>
#include <cfenv>
#include <cmath>
#include <cstdlib>
#include <cstring>
@ -289,6 +290,12 @@ namespace
{
locale_t orig = ::uselocale(loc);
#if _GLIBCXX_USE_C99_FENV_TR1
const int rounding = std::fegetround();
if (rounding != FE_TONEAREST)
std::fesetround(FE_TONEAREST);
#endif
const int save_errno = errno;
errno = 0;
char* endptr;
@ -301,6 +308,11 @@ namespace
tmpval = std::strtold(str, &endptr);
const int conv_errno = std::__exchange(errno, save_errno);
#if _GLIBCXX_USE_C99_FENV_TR1
if (rounding != FE_TONEAREST)
std::fesetround(rounding);
#endif
::uselocale(orig);
::freelocale(loc);

9
libstdc++-v3/testsuite/20_util/from_chars/4.cc
View File

@ -27,6 +27,9 @@
// Test std::from_chars floating-point conversions.
// As of July 2020 __cpp_lib_to_chars is not defined, but std::from_chars
// works for floating-point types when _GLIBCXX_HAVE_USELOCALE is defined.
#if __cpp_lib_to_chars >= 201611L || _GLIBCXX_HAVE_USELOCALE
void
test01()
{
@ -296,8 +299,7 @@ test_max_mantissa()
using Float_limits = std::numeric_limits<FloatT>;
using UInt_limits = std::numeric_limits<UIntT>;
if constexpr (Float_limits::is_iec559
&& Float_limits::digits < UInt_limits::digits)
if (Float_limits::is_iec559 && Float_limits::digits < UInt_limits::digits)
{
std::printf("Testing %d-bit float, using %zu-bit integer\n",
Float_limits::digits + (int)std::log2(Float_limits::max_exponent) + 1,
@ -355,14 +357,17 @@ test06()
test_max_mantissa<long double, unsigned __GLIBCXX_TYPE_INT_N_0>();
#endif
}
#endif
int
main()
{
#if __cpp_lib_to_chars >= 201611L || _GLIBCXX_HAVE_USELOCALE
test01();
test02();
test03();
test04();
test05();
test06();
#endif
}

6
libstdc++-v3/testsuite/20_util/from_chars/5.cc
View File

@ -25,6 +25,9 @@
// Test std::from_chars error handling.
// As of July 2020 __cpp_lib_to_chars is not defined, but std::from_chars
// works for floating-point types when _GLIBCXX_HAVE_USELOCALE is defined.
#if __cpp_lib_to_chars >= 201611L || _GLIBCXX_HAVE_USELOCALE
void
test01()
{
@ -152,12 +155,15 @@ test04()
}
}
}
#endif
int
main()
{
#if __cpp_lib_to_chars >= 201611L || _GLIBCXX_HAVE_USELOCALE
test01();
test02();
test03();
test04();
#endif
}

49
libstdc++-v3/testsuite/20_util/from_chars/6.cc Normal file
View File

@ -0,0 +1,49 @@
// Copyright (C) 2020 Free Software Foundation, Inc.
//
// This file is part of the GNU ISO C++ Library. This library is free
// software; you can redistribute it and/or modify it under the
// terms of the GNU General Public License as published by the
// Free Software Foundation; either version 3, or (at your option)
// any later version.
// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.
// You should have received a copy of the GNU General Public License along
// with this library; see the file COPYING3. If not see
// <http://www.gnu.org/licenses/>.
// <charconv> is supported in C++14 as a GNU extension
// { dg-do run { target c++14 } }
// { dg-add-options ieee }
#include <charconv>
#include <string>
#include <cfenv>
#include <testsuite_hooks.h>
void
test01()
{
#if __cpp_lib_to_chars >= 201611L || _GLIBCXX_HAVE_USELOCALE
#if _GLIBCXX_USE_C99_FENV_TR1
double d;
std::fesetround(FE_DOWNWARD);
const std::string s = "0.099999999999999999999999999";
auto res = std::from_chars(s.data(), s.data() + s.length(), d);
VERIFY( res.ec == std::errc{} );
VERIFY( res.ptr == s.data() + s.length() );
// std::from_chars should ignore the current rounding mode
// and always round to nearest.
VERIFY( d == 0.1 );
#endif
#endif
}
int
main()
{
test01();
}