working on UTC dates

README.md

@@ -78,3 +78,23 @@ It uses the *Julian year* of exactly 365.25 days, and the *TT* time scale;
 Julian epoch 2000.0 is defined to be 2000 January 1.5 (i.e. 2000 January 1d 12h), 
 which is JD 2,451,545.0 (i.e. `dso::J2000_JD`) or MJD 51,544.5 (i.e. `dso::J2000_MJD`). 
 Julian epoch is usually denoted as *“J2000.0”*.
+
+### Precision
+
+**Transforming from `datetime<T>` to `TwoPartDate`s**
+
+Transforming from a `datetime<nanoseconds>` instance to an instance of type 
+`TwoPartDate` preserves a precision better than 2e-2 nanoseconds. This is verified 
+by running the test program (unit_tests/tpdates1.cpp)[unit_tests/tpdates1.cpp]
+
+Transforming from a `datetime<microseconds>` instance to an instance of type 
+`TwoPartDate` preserves a precision better than 2e-5 microseconds. This is verified 
+by running the test program (unit_tests/tpdates2.cpp)[unit_tests/tpdates2.cpp]
+
+Transforming from a `datetime<milliseconds>` instance to an instance of type 
+`TwoPartDate` preserves a precision better than 2e-8 milliseconds. This is verified 
+by running the test program (unit_tests/tpdates3.cpp)[unit_tests/tpdates3.cpp]
+
+Transforming from a `datetime<seconds>` instance to an instance of type 
+`TwoPartDate` preserves a precision better than 2e-12 seconds. This is verified 
+by running the test program (unit_tests/tpdates4.cpp)[unit_tests/tpdates4.cpp]

src/cdatetime.hpp

@@ -34,7 +34,7 @@ constexpr const double J2000_MJD = 51544.5e0;
 /** Julian Date of Modified Julian Date zero. */
 constexpr const double MJD0_JD = 2400000.5e0;
 
-/** TT minus TAI in seconds. */
+/** TT minus TAI in [sec] */
 constexpr const double TT_MINUS_TAI = 32.184e0;
 
 } /* namespace dso */

src/datetime_tops.hpp

@@ -392,7 +392,6 @@ template <typename S, typename T = double,
 #endif
 T to_fractional_days(S nsec) noexcept {
   const T sec = static_cast<T>(nsec.__member_ref__());
-  //return sec / static_cast<T>(S::max_in_day);
   return sec / S::max_in_day;
 }
 

src/dtfund.hpp

@@ -1215,7 +1215,6 @@ class seconds {
     return m_sec;
   }
 
-private:
 /** Cast to any arithmetic type. */
 #if __cplusplus >= 202002L
   template <typename T>
@@ -1228,6 +1227,7 @@ class seconds {
     return static_cast<T>(m_sec);
   }
 
+private:
   /** The seconds as underlying type. */
   underlying_type m_sec;
 }; /* seconds */

src/tai2utc.cpp

@@ -22,6 +22,7 @@ dso::TwoPartDate dso::tai2utc(const dso::TwoPartDate &dtai) noexcept {
 }
 */
 
+/*
 double dso::tai2utc(const dso::datetime<dso::nanoseconds> &tai,
                     dso::modified_julian_day &mjd) noexcept {
   // calendar date to MJD
@@ -66,3 +67,4 @@ double dso::tai2utc(const dso::datetime<dso::nanoseconds> &tai,
 #endif
   return static_cast<double>(sec_in_day) / static_cast<double>(max_sec_in_day);
 }
+*/