libstdc++: Fix parsing of fractional seconds [PR114244]

When converting a chrono::duration<long double> to a result type with an
integer representation we should use chrono::round<_Duration> so that we
don't truncate towards zero. Rounding ensures that e.g. 0.001999s
becomes 2ms not 1ms.

We can also remove some redundant uses of chrono::duration_cast to
convert from seconds to _Duration, because the _Parser class template
requires _Duration type to be able to represent seconds without loss of
precision.

This also fixes a bug where no fractional part would be parsed for
chrono::duration<long double> because its period is ratio<1>. We should
also consider treat_as_floating_point<rep> when deciding whether to skip
reading a fractional part.

libstdc++-v3/ChangeLog:

	PR libstdc++/114244
	* include/bits/chrono_io.h (_Parser::operator()): Remove
	redundant uses of duration_cast. Use chrono::round to convert
	long double value to durations with integer representations.
	Check represenation type when deciding whether to skip parsing
	fractional seconds.
	* testsuite/20_util/duration/114244.cc: New test.
	* testsuite/20_util/duration/io.cc: Check that a floating-point
	duration with ratio<1> precision can be parsed.

diff --git a/libstdc++-v3/include/bits/chrono_io.h b/libstdc++-v3/include/bits/chrono_io.h
index 82f2d39ec44842dd49b037ab30cfd55f3de6b2b6..b8f0657bee9a11ab256e1f526380e0532aa4a265 100644 (file)
--- a/libstdc++-v3/include/bits/chrono_io.h
+++ b/libstdc++-v3/include/bits/chrono_io.h
@@ -3113,6 +3113,9 @@ namespace __detail
          unsigned __num = 0; // Non-zero for N modifier.
          bool __is_flag = false; // True if we're processing a % flag.
 
+         constexpr bool __is_floating
+           = treat_as_floating_point_v<typename _Duration::rep>;
+
          // If an out-of-range value is extracted (e.g. 61min for %M),
          // do not set failbit immediately because we might not need it
          // (e.g. parsing chrono::year doesn't care about invalid %M values).
@@ -3195,7 +3198,7 @@ namespace __detail
                          __d = day(__tm.tm_mday);
                          __h = hours(__tm.tm_hour);
                          __min = minutes(__tm.tm_min);
-                         __s = duration_cast<_Duration>(seconds(__tm.tm_sec));
+                         __s = seconds(__tm.tm_sec);
                        }
                    }
                  __parts |= _ChronoParts::_DateTime;
@@ -3564,8 +3567,8 @@ namespace __detail
                      if (!__is_failed(__err))
                        __s = seconds(__tm.tm_sec);
                    }
-                 else if constexpr (ratio_equal_v<typename _Duration::period,
-                                                  ratio<1>>)
+                 else if constexpr (_Duration::period::den == 1
+                                      && !__is_floating)
                    {
                      auto __val = __read_unsigned(__num ? __num : 2);
                      if (0 <= __val && __val <= 59) [[likely]]
@@ -3577,7 +3580,7 @@ namespace __detail
                          break;
                        }
                    }
-                 else
+                 else // Read fractional seconds
                    {
                      basic_stringstream<_CharT> __buf;
                      auto __digit = _S_try_read_digit(__is, __err);
@@ -3626,7 +3629,10 @@ namespace __detail
                          else
                            {
                              duration<long double> __fs(__val);
-                             __s = duration_cast<_Duration>(__fs);
+                             if constexpr (__is_floating)
+                               __s = __fs;
+                             else
+                               __s = chrono::round<_Duration>(__fs);
                            }
                        }
                    }
@@ -3737,7 +3743,7 @@ namespace __detail
                        {
                          __h = hours(__tm.tm_hour);
                          __min = minutes(__tm.tm_min);
-                         __s = duration_cast<_Duration>(seconds(__tm.tm_sec));
+                         __s = seconds(__tm.tm_sec);
                        }
                    }
                  __parts |= _ChronoParts::_TimeOfDay;

diff --git a/libstdc++-v3/testsuite/20_util/duration/114244.cc b/libstdc++-v3/testsuite/20_util/duration/114244.cc
new file mode 100644 (file)
index 0000000..55a7670
--- /dev/null
+++ b/libstdc++-v3/testsuite/20_util/duration/114244.cc
@@ -0,0 +1,36 @@
+// { dg-do run { target c++20 } }
+// { dg-timeout-factor 2 }
+// { dg-require-namedlocale "en_US.ISO8859-1" }
+
+// PR libstdc++/114244 Need to use round when parsing fractional seconds
+
+#include <chrono>
+#include <sstream>
+#include <testsuite_hooks.h>
+
+void
+test_pr114244()
+{
+  using namespace std::chrono;
+  seconds s;
+  milliseconds ms;
+  microseconds us;
+
+  std::istringstream is;
+
+  is.clear();
+  is.str("0.002");
+  VERIFY( is >> parse("%S", ms) );
+  VERIFY( ms == 2ms ); // not 1ms
+
+  is.imbue(std::locale(ISO_8859(1,en_US)));
+  is.clear();
+  is.str("0.002");
+  VERIFY( is >> parse("%S", us) );
+  VERIFY( us == 2000us ); // not 1999us
+}
+
+int main()
+{
+  test_pr114244();
+}

diff --git a/libstdc++-v3/testsuite/20_util/duration/io.cc b/libstdc++-v3/testsuite/20_util/duration/io.cc
index e141baf42dc8c088a48046dcf261c626b3073912..2f940ef86b791178ea2be926e4ffd3ee3d2d8e6e 100644 (file)
--- a/libstdc++-v3/testsuite/20_util/duration/io.cc
+++ b/libstdc++-v3/testsuite/20_util/duration/io.cc
@@ -200,6 +200,18 @@ test_parse()
   VERIFY( is >> parse("%S", us) );
   VERIFY( us == 976us );
   VERIFY( is.get() == '5' );
+
+  is.clear();
+  is.str("0.5");
+  std::chrono::duration<double> ds;
+  VERIFY( is >> parse("%S", ds) );
+  VERIFY( ds == 0.5s );
+
+  is.clear();
+  is.str("0.125");
+  std::chrono::duration<double, std::milli> dms;
+  VERIFY( is >> parse("%S", dms) );
+  VERIFY( dms == 0.125s );
 }
 
 int main()