diff --git a/include/boost/static_string/config.hpp b/include/boost/static_string/config.hpp
index 1b72f9e..7c61947 100644
--- a/include/boost/static_string/config.hpp
+++ b/include/boost/static_string/config.hpp
@@ -33,8 +33,15 @@
 #endif
 
 // Can we use is_constant_evaluated?
+// Standard version
 #if __cpp_lib_is_constant_evaluated >= 201811L
 #define BOOST_STATIC_STRING_USE_IS_CONST_EVAL
+#define BOOST_STATIC_STRING_IS_CONST_EVAL std::is_constant_evaluated()
+#elif defined(__clang__) && (__clang_major__ > 8)
+// If we have clang version 9+, we can use the intrinsic
+// While gcc also has this, we don't need it
+#define BOOST_STATIC_STRING_USE_IS_CONST_EVAL
+#define BOOST_STATIC_STRING_IS_CONST_EVAL __builtin_is_constant_evaluated()
 #endif
 
 // Can we use [[nodiscard]]?
@@ -56,36 +63,35 @@
 #endif
 
 #if BOOST_STATIC_STRING_STANDARD_VERSION > 201703L
+#define BOOST_STATIC_STRING_CPP20
+#define BOOST_STATIC_STRING_CPP17
+#define BOOST_STATIC_STRING_CPP14
+#define BOOST_STATIC_STRING_CPP11
 #define BOOST_STATIC_STRING_CPP20_CONSTEXPR constexpr
 #define BOOST_STATIC_STRING_CPP17_CONSTEXPR constexpr
 #define BOOST_STATIC_STRING_CPP14_CONSTEXPR constexpr
 #define BOOST_STATIC_STRING_CPP11_CONSTEXPR constexpr
-#define BOOST_STATIC_STRING_CPP20_CONSTEXPR_USED
-#define BOOST_STATIC_STRING_CPP17_CONSTEXPR_USED
-#define BOOST_STATIC_STRING_CPP14_CONSTEXPR_USED
-#define BOOST_STATIC_STRING_CPP11_CONSTEXPR_USED
-#define BOOST_STATIC_STRING_ALLOW_UNINIT_MEM
 #elif BOOST_STATIC_STRING_STANDARD_VERSION >= 201703L
+#define BOOST_STATIC_STRING_CPP17
+#define BOOST_STATIC_STRING_CPP14
+#define BOOST_STATIC_STRING_CPP11
 #define BOOST_STATIC_STRING_CPP20_CONSTEXPR
 #define BOOST_STATIC_STRING_CPP17_CONSTEXPR constexpr
 #define BOOST_STATIC_STRING_CPP14_CONSTEXPR constexpr
 #define BOOST_STATIC_STRING_CPP11_CONSTEXPR constexpr
-#define BOOST_STATIC_STRING_CPP17_CONSTEXPR_USED
-#define BOOST_STATIC_STRING_CPP14_CONSTEXPR_USED
-#define BOOST_STATIC_STRING_CPP11_CONSTEXPR_USED
 #elif BOOST_STATIC_STRING_STANDARD_VERSION >= 201402L
+#define BOOST_STATIC_STRING_CPP14
+#define BOOST_STATIC_STRING_CPP11
 #define BOOST_STATIC_STRING_CPP20_CONSTEXPR
 #define BOOST_STATIC_STRING_CPP17_CONSTEXPR
 #define BOOST_STATIC_STRING_CPP14_CONSTEXPR constexpr
 #define BOOST_STATIC_STRING_CPP11_CONSTEXPR constexpr
-#define BOOST_STATIC_STRING_CPP14_CONSTEXPR_USED
-#define BOOST_STATIC_STRING_CPP11_CONSTEXPR_USED
 #else
+#define BOOST_STATIC_STRING_CPP11
 #define BOOST_STATIC_STRING_CPP20_CONSTEXPR
 #define BOOST_STATIC_STRING_CPP17_CONSTEXPR
 #define BOOST_STATIC_STRING_CPP14_CONSTEXPR
 #define BOOST_STATIC_STRING_CPP11_CONSTEXPR constexpr
-#define BOOST_STATIC_STRING_CPP11_CONSTEXPR_USED
 #endif
 
 #ifdef BOOST_STATIC_STRING_NO_EXCEPTIONS
@@ -127,19 +133,25 @@
 
 // Compiler bug prevents constexpr from working with clang 4.x and 5.x
 // if it is detected, we disable constexpr
-#if (BOOST_STATIC_STRING_STANDARD_VERSION >= 201402L) && \
-(BOOST_STATIC_STRING_STANDARD_VERSION < 201703L) && \
+#if (BOOST_STATIC_STRING_STANDARD_VERSION >= 201402L && \
+BOOST_STATIC_STRING_STANDARD_VERSION < 201703L) && \
 defined(__clang__) && \
 ((__clang_major__ == 4) || (__clang_major__ == 5))
 // This directive works on clang
 #warning "C++14 constexpr is not supported in clang 4.x and 5.x due to a compiler bug."
-#ifdef BOOST_STATIC_STRING_CPP14_CONSTEXPR_USED
-#undef BOOST_STATIC_STRING_CPP14_CONSTEXPR_USED
+#ifdef BOOST_STATIC_STRING_CPP14
+#undef BOOST_STATIC_STRING_CPP14
 #endif
 #undef BOOST_STATIC_STRING_CPP14_CONSTEXPR
 #define BOOST_STATIC_STRING_CPP14_CONSTEXPR
 #endif
 
+//(defined(_MSVC_LANG) && BOOST_STATIC_STRING_STANDARD_VERSION < 201703L)
+#if (defined(__clang__) && (__clang_major__ < 9)) || \
+(defined(_MSVC_LANG) && !defined(BOOST_STATIC_STRING_CPP20))
+#define BOOST_STATIC_STRING_NO_PTR_COMP_FUNCTIONS
+#endif
+
 #ifndef BOOST_STATIC_STRING_STANDALONE
 #include <boost/assert.hpp>
 #include <boost/container_hash/hash.hpp>
diff --git a/include/boost/static_string/static_string.hpp b/include/boost/static_string/static_string.hpp
index 050c637..a995a4b 100644
--- a/include/boost/static_string/static_string.hpp
+++ b/include/boost/static_string/static_string.hpp
@@ -212,7 +212,7 @@ public:
   }
 
   smallest_width<N> size_{0};
-#ifdef BOOST_STATIC_STRING_ALLOW_UNINIT_MEM
+#ifdef BOOST_STATIC_STRING_CPP20
   CharT data_[N + 1];
 #else
   CharT data_[N + 1]{};
@@ -311,7 +311,7 @@ public:
     Traits::assign(data_[size_impl()], 0);
   }
 
-#ifdef BOOST_STATIC_STRING_ALLOW_UNINIT_MEM
+#ifdef BOOST_STATIC_STRING_CPP20
   CharT data_[N + 1];
 #else
   CharT data_[N + 1]{};
@@ -607,7 +607,32 @@ is_inside(
     const T* src_last,
     const T* ptr)
 {
-  return std::greater_equal<const T*>()(ptr, src_first) && 
+  // We want to make this usable in constant expressions as much as possible
+  // while retaining the guarentee that the comparison has a strict total ordering.
+  // We also want this to be fast. Since different compilers have differing levels
+  // of conformance, we will settle for the best option that is available.
+#ifdef BOOST_STATIC_STRING_NO_PTR_COMP_FUNCTIONS 
+#ifdef BOOST_STATIC_STRING_USE_IS_CONST_EVAL
+  // Our second best option is to use is_constant_evaluated
+  // and a loop that checks for equality, since equality for 
+  // pointer to object types is never unspecified in this case.
+  if (BOOST_STATIC_STRING_IS_CONST_EVAL)
+  {
+    for (; src_first != src_last; ++src_first)
+      if (src_first == ptr)
+        return true;
+    return false;
+  }
+#else
+  // If library comparison functions don't work, then
+  // its almost certain that we can use the builtin
+  // comparison operator instead.
+  return ptr >= src_first && ptr <= src_last;
+#endif
+#endif
+  // Use the library comparison functions if we can't use 
+  // is_constant_evaluated or if we don't need to.
+  return std::greater_equal<const T*>()(ptr, src_first) &&
     std::less_equal<const T*>()(ptr, src_last);
 }
 } // detail
@@ -4739,7 +4764,7 @@ BOOST_STATIC_STRING_CPP11_CONSTEXPR
 basic_static_string<N, CharT, Traits>::
 basic_static_string() noexcept
 {
-#ifdef BOOST_STATIC_STRING_CPP20_CONSTEXPR_USED
+#ifdef BOOST_STATIC_STRING_CPP20
   term();
 #endif
 }
@@ -5316,7 +5341,7 @@ replace(
   n1 = (std::min)(n1, curr_size - pos);
   Traits::move(&curr_data[pos + n2], &curr_data[pos + n1], curr_size - pos - n1 + 1);
   Traits::assign(&curr_data[pos], n2, c);
-  this->set_size(curr_size + (n2 - n1));
+  this->set_size((curr_size + n2) - n1);
   return *this;
 }
 
@@ -5377,7 +5402,7 @@ replace(
       Traits::move(&curr_data[pos + n2], &curr_data[pos + n1], curr_size - pos - n1 + 1);
     }
   }
-  this->set_size(curr_size + (n2 - n1));
+  this->set_size((curr_size + n2) - n1);
   return *this;
 }
 
@@ -5414,7 +5439,7 @@ replace(
   n1 = (std::min)(n1, curr_size - pos);
   // Move everything from the end of the splice point to the end of the rotated string to the begining of the splice point
   Traits::move(&curr_data[pos + n2], &curr_data[pos + n2 + n1], (curr_size + (n2 - n1)) - pos);
-  this->set_size(curr_size + (n2 - n1));
+  this->set_size((curr_size + n2) - n1);
   return *this;
 }
 
@@ -5603,7 +5628,7 @@ replace_unchecked(
     n1 = curr_size - pos;
   Traits::move(&curr_data[pos + n2], &curr_data[pos + n1], curr_size - pos - n1 + 1);
   Traits::copy(&curr_data[pos], s, n2);
-  this->set_size(curr_size + (n2 - n1));
+  this->set_size((curr_size + n2) - n1);
   return *this;
 }
 
diff --git a/test/constexpr_tests.hpp b/test/constexpr_tests.hpp
index 0b482c9..e3dd8d0 100644
--- a/test/constexpr_tests.hpp
+++ b/test/constexpr_tests.hpp
@@ -11,7 +11,7 @@
 #include <boost/static_string/static_string.hpp>
 
 // char_traits aren't constexpr until c++17
-#ifdef BOOST_STATIC_STRING_CPP14_CONSTEXPR_USED
+#if BOOST_STATIC_STRING_STANDARD_VERSION <= 201703L
 struct cxper_char_traits
 {
   using char_type = char;
@@ -43,7 +43,7 @@ constexpr
 bool 
 testConstantEvaluation()
 {
-#ifdef BOOST_STATIC_STRING_CPP20_CONSTEXPR_USED
+#ifdef BOOST_STATIC_STRING_CPP20
   // c++20 constexpr tests
   cstatic_string a;
   cstatic_string b(1, 'a');
@@ -230,7 +230,7 @@ testConstantEvaluation()
   a.ends_with("a");
 
   return true;
-#elif defined(BOOST_STATIC_STRING_CPP17_CONSTEXPR_USED)
+#elif defined(BOOST_STATIC_STRING_CPP17)
   //c++17 constexpr tests
 
     // ctors
@@ -419,7 +419,7 @@ testConstantEvaluation()
   a.ends_with("a");
  
   return true;
-#elif defined(BOOST_STATIC_STRING_CPP14_CONSTEXPR_USED)
+#elif defined(BOOST_STATIC_STRING_CPP14)
   // c++14 constexpr tests
 
   // ctors
@@ -593,7 +593,7 @@ testConstantEvaluation()
   a.ends_with('a');
   a.ends_with("a");
   return true;
-#elif defined(BOOST_STATIC_STRING_CPP11_CONSTEXPR_USED)
+#elif defined(BOOST_STATIC_STRING_CPP11)
   // c++11 constexpr tests
   return cstatic_string().size() + 
     cstatic_string().empty() + 
diff --git a/test/static_string.cpp b/test/static_string.cpp
index 57f4f7e..e8edc2d 100644
--- a/test/static_string.cpp
+++ b/test/static_string.cpp
@@ -1,6 +1,6 @@
 //
 // Copyright (c) 2016-2019 Vinnie Falco (vinnie dot falco at gmail dot com)
-// Copyright (c) 2019 Krystian Stasiowski (sdkrystian at gmail dot com)
+// Copyright (c) 2019-2020 Krystian Stasiowski (sdkrystian at gmail dot com)
 //
 // Distributed under the Boost Software License, Version 1.0. (See accompanying
 // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)