some fix

include/pocketpy/common/str.hpp

@@ -13,8 +13,6 @@
 
 namespace pkpy {
 
-struct SStream;
-
 struct Str: pkpy_Str {
     bool is_inlined() const { return is_sso; }
 

src/common/sstream.c

@@ -35,11 +35,11 @@ void pkpy_SStream__write_float(pkpy_SStream* self, float val, int precision){
 }
 
 void pkpy_SStream__write_double(pkpy_SStream* self, double val, int precision){
-    if(val == INFINITY) {
+    if(isinf(val)) {
         pkpy_SStream__write_cstr(self, val > 0 ? "inf" : "-inf");
         return;
     }
-    if(val == NAN) {
+    if(isnan(val)) {
         pkpy_SStream__write_cstr(self, "nan");
         return;
     }