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* [gcc r11-5722] libstdc++: Add std::bit_cast for C++20 [PR 93121]
@ 2020-12-03 19:17 Jonathan Wakely
0 siblings, 0 replies; only message in thread
From: Jonathan Wakely @ 2020-12-03 19:17 UTC (permalink / raw)
To: gcc-cvs, libstdc++-cvs
https://gcc.gnu.org/g:9e433b3461ab64b38350817392a77efb67bb78b4
commit r11-5722-g9e433b3461ab64b38350817392a77efb67bb78b4
Author: Jonathan Wakely <jwakely@redhat.com>
Date: Thu Dec 3 19:17:13 2020 +0000
libstdc++: Add std::bit_cast for C++20 [PR 93121]
Thanks to Jakub's addition of the built-in, we can add this to the
library now. The compiler tests for the built-in are quite extensive,
including verifying the constraints, so this only adds minimal tests to
the library testsuite.
This doesn't add a new _GLIBCXX_HAVE_BUILTIN_BIT_CAST because using
__has_builtin(__builtin_bit_cast) works for GCC and versions of Clang
that provide the built-in.
libstdc++-v3/ChangeLog:
PR libstdc++/93121
* include/std/bit (__cpp_lib_bit_cast, bit_cast): Define.
* include/std/version (__cpp_lib_bit_cast): Define.
* testsuite/26_numerics/bit/bit.cast/bit_cast.cc: New test.
* testsuite/26_numerics/bit/bit.cast/version.cc: New test.
Diff:
---
libstdc++-v3/include/std/bit | 12 ++++
libstdc++-v3/include/std/version | 3 +
.../testsuite/26_numerics/bit/bit.cast/bit_cast.cc | 81 ++++++++++++++++++++++
.../testsuite/26_numerics/bit/bit.cast/version.cc | 27 ++++++++
4 files changed, 123 insertions(+)
diff --git a/libstdc++-v3/include/std/bit b/libstdc++-v3/include/std/bit
index 16f7eba46d7..1d99c807c4a 100644
--- a/libstdc++-v3/include/std/bit
+++ b/libstdc++-v3/include/std/bit
@@ -49,6 +49,18 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
* @{
*/
+#if __cplusplus > 201703l && __has_builtin(__builtin_bit_cast)
+#define __cpp_lib_bit_cast 201806L
+
+ /// Create a value of type `To` from the bits of `from`.
+ template<typename _To, typename _From>
+ constexpr _To
+ bit_cast(const _From& __from) noexcept
+ {
+ return __builtin_bit_cast(_To, __from);
+ }
+#endif
+
/// @cond undoc
template<typename _Tp>
diff --git a/libstdc++-v3/include/std/version b/libstdc++-v3/include/std/version
index 25f628f399d..6e4bd99b361 100644
--- a/libstdc++-v3/include/std/version
+++ b/libstdc++-v3/include/std/version
@@ -201,6 +201,9 @@
# define __cpp_lib_atomic_wait 201907L
#endif
#define __cpp_lib_bind_front 201907L
+#if __has_builtin(__builtin_bit_cast)
+# define __cpp_lib_bit_cast 201806L
+#endif
// FIXME: #define __cpp_lib_execution 201902L
#define __cpp_lib_integer_comparison_functions 202002L
#define __cpp_lib_constexpr_algorithms 201806L
diff --git a/libstdc++-v3/testsuite/26_numerics/bit/bit.cast/bit_cast.cc b/libstdc++-v3/testsuite/26_numerics/bit/bit.cast/bit_cast.cc
new file mode 100644
index 00000000000..b451f152b47
--- /dev/null
+++ b/libstdc++-v3/testsuite/26_numerics/bit/bit.cast/bit_cast.cc
@@ -0,0 +1,81 @@
+// 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/>.
+
+// { dg-options "-std=gnu++2a" }
+// { dg-do compile { target c++2a } }
+
+#include <bit>
+
+#ifndef __cpp_lib_bit_cast
+# error "Feature-test macro for bit_cast wait missing in <bit>"
+#elif __cpp_lib_bit_cast != 201806L
+# error "Feature-test macro for bit_cast wait has wrong value in <bit>"
+#endif
+
+#include <cstdint>
+#include <cstring>
+#include <testsuite_hooks.h>
+
+template<typename To, typename From>
+constexpr bool
+check(const From& from)
+{
+ return std::bit_cast<From>(std::bit_cast<To>(from)) == from;
+}
+
+void
+test01()
+{
+ static_assert( std::bit_cast<int>(123) == 123 );
+ static_assert( std::bit_cast<int>(123u) == 123 );
+ static_assert( std::bit_cast<int>(~0u) == ~0 );
+
+ if constexpr (sizeof(int) == sizeof(float))
+ static_assert( check<int>(12.34f) );
+ if constexpr (sizeof(unsigned long long) == sizeof(double))
+ static_assert( check<unsigned long long>(123.456) );
+ if constexpr (sizeof(std::intptr_t) == sizeof(void(*)()))
+ VERIFY( check<std::intptr_t>(&test01) );
+}
+
+void
+test02()
+{
+ struct S
+ {
+ int i;
+
+ bool operator==(const char* s) const
+ { return std::memcmp(&i, s, sizeof(i)) == 0; }
+ };
+
+ char arr[sizeof(int)];
+ char arr2[sizeof(int)];
+ for (int i = 0; i < sizeof(int); ++i)
+ {
+ arr[i] = i + 1;
+ arr2[i] = (i + 1) * -(i % 2);
+ }
+ VERIFY( std::bit_cast<S>(arr) == arr );
+ VERIFY( std::bit_cast<S>(arr2) == arr2 );
+}
+
+int main()
+{
+ test01();
+ test02();
+}
diff --git a/libstdc++-v3/testsuite/26_numerics/bit/bit.cast/version.cc b/libstdc++-v3/testsuite/26_numerics/bit/bit.cast/version.cc
new file mode 100644
index 00000000000..688d44bbb89
--- /dev/null
+++ b/libstdc++-v3/testsuite/26_numerics/bit/bit.cast/version.cc
@@ -0,0 +1,27 @@
+// 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/>.
+
+// { dg-options "-std=gnu++2a" }
+// { dg-do compile { target c++2a } }
+
+#include <version>
+
+#ifndef __cpp_lib_bit_cast
+# error "Feature-test macro for bit_cast wait missing in <version>"
+#elif __cpp_lib_bit_cast != 201806L
+# error "Feature-test macro for bit_cast wait has wrong value in <version>"
+#endif
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