fixed performance degradation (#272)

Makefile

@@ -66,6 +66,9 @@ fuzz: test/src/fuzz.cpp src/json.hpp
 cppcheck:
 	cppcheck --enable=warning --inconclusive --force --std=c++11 src/json.hpp --error-exitcode=1
 
+clang_sanitize: clean
+	CXX=clang++ CXXFLAGS="-g -O2 -fsanitize=address -fsanitize=undefined -fno-omit-frame-pointer" $(MAKE)
+
 ##########################################################################
 # maintainer targets
 ##########################################################################

src/json.hpp

@@ -2232,7 +2232,8 @@ class basic_json
     {
         std::stringstream ss;
         // fix locale problems
-        ss.imbue(std::locale(std::locale(), new DecimalSeparator));
+        const static std::locale loc(std::locale(), new DecimalSeparator);
+        ss.imbue(loc);
 
         // 6, 15 or 16 digits of precision allows round-trip IEEE 754
         // string->float->string, string->double->string or string->long

src/json.hpp.re2c

@@ -2232,7 +2232,8 @@ class basic_json
     {
         std::stringstream ss;
         // fix locale problems
-        ss.imbue(std::locale(std::locale(), new DecimalSeparator));
+        const static std::locale loc(std::locale(), new DecimalSeparator);
+        ss.imbue(loc);
 
         // 6, 15 or 16 digits of precision allows round-trip IEEE 754
         // string->float->string, string->double->string or string->long