From 07b78fd58464c1cef9a86b2502ee2c44f3a59171 Mon Sep 17 00:00:00 2001
From: Matt Borland <matt@mattborland.com>
Date: Mon, 28 Aug 2023 11:01:20 -0400
Subject: [PATCH] Fix issue #1023

---
 include/boost/math/concepts/real_concept.hpp |  8 ++++++--
 include/boost/math/tools/config.hpp          | 10 +++++-----
 include/boost/math/tools/promotion.hpp       |  4 +++-
 3 files changed, 14 insertions(+), 8 deletions(-)

diff --git a/include/boost/math/concepts/real_concept.hpp b/include/boost/math/concepts/real_concept.hpp
index 56e4342e6b..565d58e421 100644
--- a/include/boost/math/concepts/real_concept.hpp
+++ b/include/boost/math/concepts/real_concept.hpp
@@ -45,8 +45,12 @@
 #  include <cstdio>
 #endif
 
-#if __has_include(<stdfloat>)
-#  include <stdfloat>
+#if defined __has_include
+#  if __cplusplus > 202002L || _MSVC_LANG > 202002L 
+#    if __has_include (<stdfloat>)
+#    include <stdfloat>
+#    endif
+#  endif
 #endif
 
 namespace boost{ namespace math{
diff --git a/include/boost/math/tools/config.hpp b/include/boost/math/tools/config.hpp
index 8316c0bc78..b1d93bc3d2 100644
--- a/include/boost/math/tools/config.hpp
+++ b/include/boost/math/tools/config.hpp
@@ -152,11 +152,11 @@
      // libstdc++3 only defines to/from_chars for std::float128_t when one of these defines are set
      // otherwise we're right out of luck...
 #    if defined(_GLIBCXX_LDOUBLE_IS_IEEE_BINARY128) || defined(_GLIBCXX_HAVE_FLOAT128_MATH)
-#    include <cstring> // std::strlen is used with from_chars
-#    include <charconv>
-#    include <stdfloat>
-#    define BOOST_MATH_USE_CHARCONV_FOR_CONVERSION
-#endif
+#      include <cstring> // std::strlen is used with from_chars
+#      include <charconv>
+#      include <stdfloat>
+#      define BOOST_MATH_USE_CHARCONV_FOR_CONVERSION
+#    endif
 #  endif
 #endif
 
diff --git a/include/boost/math/tools/promotion.hpp b/include/boost/math/tools/promotion.hpp
index 7b7789d037..842022694e 100644
--- a/include/boost/math/tools/promotion.hpp
+++ b/include/boost/math/tools/promotion.hpp
@@ -27,8 +27,10 @@
 #include <type_traits>
 
 #if defined __has_include
-#  if __has_include (<stdfloat>)
+#  if __cplusplus > 202002L || _MSVC_LANG > 202002L 
+#    if __has_include (<stdfloat>)
 #    include <stdfloat>
+#    endif
 #  endif
 #endif