better support for file size in 64 bits

include/spdlog/details/file_helper.h

@@ -100,9 +100,7 @@ public:
     {
         if (!_fd)
             throw spdlog_ex("Cannot use size() on closed file " + os::filename_to_str(_filename));
-
 		return os::filesize(_fd); 
-        
     }
 
     const filename_t& filename() const

include/spdlog/details/os.h

@@ -186,43 +186,41 @@ inline bool file_exists(const filename_t& filename)
 #endif
 }
 
+
+
+
 //Return file size according to open FILE* object
 inline size_t filesize(FILE *f)
 {
+	if (f == nullptr)
+		throw spdlog_ex("Failed getting file size. fd is null");
 #ifdef _WIN32
-#if _WIN64 //64 bits
 	int fd = _fileno(f);
+#if _WIN64 //64 bits		
 	struct _stat64 st;	
 	if (_fstat64(fd, &st) == 0)
 		return st.st_size;
-	else
-		throw spdlog_ex("Failed getting file size from fd", errno);
+			
 #else //windows 32 bits		
-	int fd = _fileno(f);
 	struct _stat st;
 	if (_fstat(fd, &st) == 0)
 		return st.st_size;
-	else
-		throw spdlog_ex("Failed getting file size from fd", errno);
 #endif
 
-#else// common unix
-	#if __x86_64__ || __ppc64__ //64 bits
-	int fd = fileno(f)
+#else // unix
+	int fd = fileno(f);
+	//64 bits(but not in osx, where fstat64 is deprecated)
+	#if !defined(__APPLE__) && (defined(__x86_64__) || defined(__ppc64__)) 
 	struct stat64 st;
 	if (fstat64(fd, &st) == 0)
 		return st.st_size;	
-	else
-		throw spdlog_ex("Failed getting file size from fd", errno);
-#else //unix 32 bits
-	int fd = fileno(f)
+#else // unix 32 bits or osx	
 	struct stat st;
 	if (fstat(fd, &st) == 0)
 		return st.st_size;	
-	else
+#endif
+#endif
 	throw spdlog_ex("Failed getting file size from fd", errno);
-#endif
-#endif
 }