update source to Ceph Pacific 16.2.2

[ceph.git] / ceph / src / boost / libs / multiprecision / config / has_is_constant_evaluated.cpp

diff --git a/ceph/src/boost/libs/multiprecision/config/has_is_constant_evaluated.cpp b/ceph/src/boost/libs/multiprecision/config/has_is_constant_evaluated.cpp
index 808c396fe7c497710709911245f7f97198158592..4dac95b29e8597735d865b6e462786ec59cbf723 100644 (file)
--- a/ceph/src/boost/libs/multiprecision/config/has_is_constant_evaluated.cpp
+++ b/ceph/src/boost/libs/multiprecision/config/has_is_constant_evaluated.cpp
@@ -3,8 +3,45 @@
 //  Boost Software License, Version 1.0. (See accompanying file
 //  LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
 
+// This program determines if std::is_constant_evaluated  is available to switch within a function to use compile-time constexp calculations.
+// See https://en.cppreference.com/w/cpp/types/is_constant_evaluated
+// and https://en.cppreference.com/w/cpp/compiler_support
+// Currently only GCC 9 and Clang 9 and <cxxflags>-std=c++2a or  b2 cxxstd=2a
+
+// https://clang.llvm.org/docs/LanguageExtensions.html#builtin-macros
+
+// From Clang 10 onwards, __has_builtin(__X) can be used.  but also works for Clang 9
+
+// boost\libs\multiprecision\config>b2 has_is_constant_evaluated toolset=clang-win-9.0.0 cxxstd=2a address-model=64 release  >  mp_is_const_eval_30Sep2019.log
+
+#include <boost/config.hpp>
+#include <boost/config/pragma_message.hpp>
+
 #include <boost/multiprecision/number.hpp>
 
+#ifdef __has_builtin
+BOOST_PRAGMA_MESSAGE (" __has_builtin is defined.")
+
+#  if __has_builtin(__builtin_is_constant_evaluated)
+BOOST_PRAGMA_MESSAGE (" __has_builtin(__builtin_is_constant_evaluated), so BOOST_MP_NO_CONSTEXPR_DETECTION should NOT be defined.")
+#  endif // __has_builtin(__builtin_is_constant_evaluated)
+
+#endif // __has_builtin
+
+#ifdef BOOST_MP_HAS_IS_CONSTANT_EVALUATED
+BOOST_PRAGMA_MESSAGE ("BOOST_MP_HAS_IS_CONSTANT_EVALUATED defined.")
+#else
+BOOST_PRAGMA_MESSAGE ("BOOST_MP_HAS_IS_CONSTANT_EVALUATED is NOT defined, so no std::is_constant_evaluated() from std library.")
+#endif
+
+#ifdef BOOST_NO_CXX14_CONSTEXPR
+BOOST_PRAGMA_MESSAGE ("BOOST_NO_CXX14_CONSTEXPR is defined.")
+#endif
+
+#ifdef BOOST_NO_CXX17_CONSTEXPR
+BOOST_PRAGMA_MESSAGE ("BOOST_NO_CXX17_CONSTEXPR is defined.")
+#endif
+
 #ifdef BOOST_MP_NO_CONSTEXPR_DETECTION
-#error 1
+#  error 1  "std::is_constant_evaluated is NOT available to determine if a calculation can use constexpr."
 #endif