Change utility functions to use more efficient runtime versions when invoked at runtime

include/rexy/utility.hpp

@@ -22,6 +22,9 @@
 #include <utility> //forward, move
 #include <cstdlib> //size_t
 #include <type_traits>
+#include <cstring> //strlen, strcmp, memcpy
+#include <cwchar> //wcslen
+#include <string> //char_traits
 
 #include "rexy.hpp"
 
@@ -83,6 +86,42 @@ namespace rexy{
 		{
 			return cmp(l, r) ? l : r;
 		}
+
+#ifdef __cpp_lib_is_constant_evaluated
+		template<class T>
+		constexpr size_t strlen(const T* c)noexcept{
+			return std::char_traits<T>::length(c);
+		}
+		template<class T>
+		constexpr int strcmp(const T* l, const T* r)noexcept{
+			if(!std::is_constant_evaluated()){
+				if(std::is_same_v<std::remove_cvref_t<T>,char>){
+					return std::strcmp(l, r);
+				}else if(std::is_same_v<std::remove_cvref_t<T>,wchar_t>){
+					return std::wcscmp(l, r);
+				}
+			}
+			for(;*l == *r && *l;++l, ++r);
+			return *l - *r;
+		}
+		template<class T, class Compare>
+		constexpr int strcmp(const T* l, const T* r, Compare cmp)noexcept{
+			for(;cmp(*l, *r) && *l;++l, ++r);
+			return *l - *r;
+		}
+		constexpr void memcpy(void* l, const void* r, size_t n){
+			if(!std::is_constant_evaluated()){
+				std::memcpy(l, r, n);
+			}else{
+				char* ld = static_cast<char*>(l);
+				const char* rd = static_cast<const char*>(r);
+				for(size_t i = 0;i < n;++i){
+					ld[i] = rd[i];
+				}
+			}
+		}
+	}
+#else //__cpp_lib_is_constant_evaluated
 		template<class T>
 		constexpr size_t strlen(const T* c)noexcept{
 			size_t i = 0;
@@ -107,6 +146,7 @@ namespace rexy{
 			}
 		}
 	}
+#endif //__cpp_lib_is_constant_evaluated
 
 }