re PR libstdc++/9151 (std::setprecision limited to 16 digits when outputting a double to a stream)

2003-01-06  Paolo Carlini  <pcarlini@unitus.it>

	PR libstdc++/9151
	* include/bits/locale_facets.cc (num_put::_M_convert_float):
	Limit __prec to digits10 + 2, not digits10 + 1, taking into
	account the possibility of %{g,G} conversion specifiers
	inside _S_format_float.
	* testsuite/27_io/ostream_inserter_arith.cc (test06): Add.

From-SVN: r60939

libstdc++-v3/ChangeLog

+2003-01-06  Paolo Carlini  <pcarlini@unitus.it>
+
+	PR libstdc++/9151
+	* include/bits/locale_facets.cc (num_put::_M_convert_float):
+	Limit __prec to digits10 + 2, not digits10 + 1, taking into
+	account the possibility of %{g,G} conversion specifiers
+	inside _S_format_float.
+	* testsuite/27_io/ostream_inserter_arith.cc (test06): Add.
+
 2003-01-06  Kaveh R. Ghazi  <ghazi@caip.rutgers.edu>
 
 	* testsuite/lib/libstdc++-v3-dg.exp (libstdc++-v3-init,

libstdc++-v3/include/bits/locale_facets.tcc

@@ -622,9 +622,14 @@ namespace std
       _M_convert_float(_OutIter __s, ios_base& __io, _CharT __fill, char __mod,
 		       _ValueT __v) const
       {
-	// Note: digits10 is rounded down.  We need to add 1 to ensure
+	// Note: digits10 is rounded down: we need to add 1 to ensure
 	// we get the full available precision.
-	const int __max_digits = numeric_limits<_ValueT>::digits10 + 1;
+	// Then, in general, one more 1 needs to be added since, when the
+	// %{g,G} conversion specifiers are chosen inside _S_format_float, the
+	// precision field is "the maximum number of significant digits", *not*
+	// the "number of digits to appear after the decimal point", as happens
+	// for %{e,E,f,F} (C99, 7.19.6.1,4).
+	const int __max_digits = numeric_limits<_ValueT>::digits10 + 2;
 	streamsize __prec = __io.precision();
 
 	if (__prec > static_cast<streamsize>(__max_digits))

libstdc++-v3/testsuite/27_io/ostream_inserter_arith.cc

@@ -368,7 +368,26 @@ test05()
   istringstream istr (sval);
   double d;
   istr >> d;
-  VERIFY (abs(pi-d)/pi < DBL_EPSILON);
+  VERIFY( abs(pi-d)/pi < DBL_EPSILON );
+  return 0;
+}
+
+
+// libstdc++/9151
+int
+test06()
+{
+  int prec = numeric_limits<double>::digits10 + 2;
+  double oval = numeric_limits<double>::min();
+
+  stringstream ostr;
+  ostr.precision(prec);
+  ostr << oval;
+  string sval = ostr.str();
+  istringstream istr (sval);
+  double ival;
+  istr >> ival;
+  VERIFY( abs(oval-ival)/oval < DBL_EPSILON ); 
   return 0;
 }
 
@@ -380,6 +399,7 @@ main()
   test03();
   test04();
   test05();
+  test06();
 #ifdef TEST_NUMPUT_VERBOSE
   cout << "Test passed!" << endl;
 #endif