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* [gcc(refs/users/giulianob/heads/autopar_rebase2)] libstdc++: Make std::from_chars always round to nearest
@ 2020-08-18 1:12 Giuliano Belinassi
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From: Giuliano Belinassi @ 2020-08-18 1:12 UTC (permalink / raw)
To: gcc-cvs, libstdc++-cvs
https://gcc.gnu.org/g:b583d3f8d6ad3c26f8efc5d7dbee9f9969a593a0
commit b583d3f8d6ad3c26f8efc5d7dbee9f9969a593a0
Author: Jonathan Wakely <jwakely@redhat.com>
Date: Mon Jul 27 15:51:16 2020 +0100
libstdc++: Make std::from_chars always round to nearest
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.
Diff:
---
libstdc++-v3/src/c++17/floating_from_chars.cc | 12 +++++++
libstdc++-v3/testsuite/20_util/from_chars/4.cc | 9 +++--
libstdc++-v3/testsuite/20_util/from_chars/5.cc | 6 ++++
libstdc++-v3/testsuite/20_util/from_chars/6.cc | 49 ++++++++++++++++++++++++++
4 files changed, 74 insertions(+), 2 deletions(-)
diff --git a/libstdc++-v3/src/c++17/floating_from_chars.cc b/libstdc++-v3/src/c++17/floating_from_chars.cc
index 45de2be283d..f1519e5c7b6 100644
--- a/libstdc++-v3/src/c++17/floating_from_chars.cc
+++ b/libstdc++-v3/src/c++17/floating_from_chars.cc
@@ -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);
diff --git a/libstdc++-v3/testsuite/20_util/from_chars/4.cc b/libstdc++-v3/testsuite/20_util/from_chars/4.cc
index 6d692592e95..e7127ed0c48 100644
--- a/libstdc++-v3/testsuite/20_util/from_chars/4.cc
+++ b/libstdc++-v3/testsuite/20_util/from_chars/4.cc
@@ -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
}
diff --git a/libstdc++-v3/testsuite/20_util/from_chars/5.cc b/libstdc++-v3/testsuite/20_util/from_chars/5.cc
index f8fc7f6cd12..9525da8aebe 100644
--- a/libstdc++-v3/testsuite/20_util/from_chars/5.cc
+++ b/libstdc++-v3/testsuite/20_util/from_chars/5.cc
@@ -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
}
diff --git a/libstdc++-v3/testsuite/20_util/from_chars/6.cc b/libstdc++-v3/testsuite/20_util/from_chars/6.cc
new file mode 100644
index 00000000000..e592b2eb806
--- /dev/null
+++ b/libstdc++-v3/testsuite/20_util/from_chars/6.cc
@@ -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();
+}
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