Re: [Boost-bugs] [Boost C++ Libraries] #5428: No <ctime> function in Windows CE 6.0

Subject: Re: [Boost-bugs] [Boost C++ Libraries] #5428: No <ctime> function in Windows CE 6.0
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2012-01-30 17:45:43

#5428: No <ctime> function in Windows CE 6.0
--------------------------------------------------------+-------------------
  Reporter:  Akira Takahashi <faithandbrave@…>          |       Owner:  az_sw_dude
      Type:  Bugs                                       |      Status:  new       
 Milestone:  To Be Determined                           |   Component:  date_time 
   Version:  Boost 1.46.1                               |    Severity:  Problem   
Resolution:                                             |    Keywords:  wince     
--------------------------------------------------------+-------------------

Comment (by Ulrich Eckhardt <ulrich.eckhardt@…>):

 The above implementation of localtime from sqlite is incorrect, AFAICT.
 The problem is that the tm_yday and tm_isdst fields are not set correctly.
 Further, even the hour differs sometimes, which I guess might be due to
 the daylight saving time offsets. I haven't completely figured out how to
 pull that info out of the system.


 The code for gmtime() below was tested on a German MS Windows XP system
 for time_t values between 1 and 0xfffffff8, using the native gmtime()
 implementation of VC8 as reference. Both yield the same results. This also
 runs on MS Windows CE6, though I still need to test a few checkpoint
 values since I don't have a native gmtime() at my service there.

 I'm a bit unsure if I can simply set the tm_isdst to zero for gmtime(),
 maybe someone else could jump in here.

 {{{
       //! requires a pointer to a user created std::tm struct
       inline
       static std::tm* gmtime(const std::time_t* t, std::tm* result)
       {
         /* Three conversions here:
          1. convert to 64-bit type to avoid overflows
          2. epoch beginning 1970 to one beginning 1601
          3. seconds to 100ns steps */
         int64_t t64 = static_cast<int64_t>(*t);
         t64 += 11644473600;
         t64 *= 10000000;
         // convert to FILETIME struct
         FILETIME utc_time;
         utc_time.dwLowDateTime = static_cast<DWORD>(t64 & 0xFFFFFFFF);
         utc_time.dwHighDateTime= static_cast<DWORD>(t64 >> 32);
         // split into year, month, day etc
         SYSTEMTIME st;
         if(!FileTimeToSystemTime(&utc_time, &st))
           boost::throw_exception(std::runtime_error("could not convert
 calendar time to local time"));
         result->tm_year = st.wYear - 1900;
         result->tm_mon = st.wMonth - 1;
         result->tm_wday = st.wDayOfWeek;
         result->tm_mday = st.wDay;
         result->tm_hour = st.wHour;
         result->tm_min = st.wMinute;
         result->tm_sec = st.wSecond;
         // compute day of year
         bool leapyear;
         if((st.wYear % 1000) == 0)
             leapyear = true;
         else if((st.wYear % 100) == 0)
             leapyear = false;
         else if((st.wYear % 4) == 0)
             leapyear = true;
         else
             leapyear = false;
         result->tm_yday = result->tm_mday - 1;
         if(leapyear)
         {
           int const ml[] = {31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30,
 31};
           for(int i=0; i!=result->tm_mon; ++i)
             result->tm_yday += ml[i];
         }
         else
         {
           int const ml[] = {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30,
 31};
           for(int i=0; i!=result->tm_mon; ++i)
             result->tm_yday += ml[i];
         }

         /* MSVC8 implementation always does that, using a German MS
 Windows XP,
         not sure if that is correct... */
         result->tm_isdst = 0;

         return result;
       }
 }}}

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/5428#comment:3>
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