[libc++] reduce <complex> parsing time

[nick]

Summary

Instead of including <ios> for ios_base::failbit simply get failbit member of the template argument.
Print directly to a stream instead of using intermediate ostringstream.

Parsing time: 874ms -> 164ms (-81%)

[ldionne]

Do you have commit access?

libcxx/include/complex

1444

I'm thinking there must be a reason why it was written that way, but I can't think of any and your version indeed seems more straightforward.

[nick]

No, I do not have commit rights.

libcxx/include/complex

1444

I tried to dig into history and the code is from initial commit, so I hoped I will get insights during the review.

[ldionne]

Thanks for the patch!

[cantonios]

libcxx/include/complex

1444

It was written this way to respect properties like field width. This now breaks fixed-width printing of complex numbers.

See https://reviews.llvm.org/D78816

[nick]

libcxx/include/complex

1444

Right, @ldionne could you please revert the commit as I do not have a fix for that

libcxx/include/complex

 }  // std
 
 */
 
 #include <__config>
 #include <type_traits>
 #include <stdexcept>
 #include <cmath>
-#include <sstream>
+#include <iosfwd>
 #include <version>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #pragma GCC system_header
 #endif
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
if (__is.good())
                         ws(__is);
                         __c = __is.peek();
                         if (__c == _CharT(')'))
                         {
                             __is.get();
                             __x = complex<_Tp>(__r, __i);
                         }
                         else
-                            __is.setstate(ios_base::failbit);
+                            __is.setstate(__is.failbit);
                     }
                     else
-                        __is.setstate(ios_base::failbit);
+                        __is.setstate(__is.failbit);
                 }
                 else if (__c == _CharT(')'))
                 {
                     __is.get();
                     __x = complex<_Tp>(__r, _Tp(0));
                 }
                 else
-                    __is.setstate(ios_base::failbit);
+                    __is.setstate(__is.failbit);
             }
             else
-                __is.setstate(ios_base::failbit);
+                __is.setstate(__is.failbit);
         }
         else
         {
             _Tp __r;
             __is >> __r;
             if (!__is.fail())
                 __x = complex<_Tp>(__r, _Tp(0));
             else
-                __is.setstate(ios_base::failbit);
+                __is.setstate(__is.failbit);
         }
     }
     else
-        __is.setstate(ios_base::failbit);
+        __is.setstate(__is.failbit);
     return __is;
 }
 
 template<class _Tp, class _CharT, class _Traits>
 basic_ostream<_CharT, _Traits>&
 operator<<(basic_ostream<_CharT, _Traits>& __os, const complex<_Tp>& __x)
 {
-    basic_ostringstream<_CharT, _Traits> __s;
-    __s.flags(__os.flags());
-    __s.imbue(__os.getloc());
-    __s.precision(__os.precision());
-    __s << '(' << __x.real() << ',' << __x.imag() << ')';
-    return __os << __s.str();
+    return __os << '(' << __x.real() << ',' << __x.imag() << ')';
 }
 
 #if _LIBCPP_STD_VER > 11
 // Literal suffix for complex number literals [complex.literals]
 inline namespace literals
 {
   inline namespace complex_literals
   {