[GitHub] [incubator-nuttx] patacongo commented on pull request #4693: time: Typedef time_t to uint64_t if CONFIG_SYSTEM_TIME64 is defined

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patacongo commented on pull request #4693:
URL: https://github.com/apache/incubator-nuttx/pull/4693#issuecomment-946728343


   > > if we need 32 bit version, it should be unsigned, as int32_t will wrap too soon. i guess 64 bit version should be unsigned too because it should be consistent within nuttx.
   > 
   > Yes, int32_t will wrap at 2038(https://en.wikipedia.org/wiki/Year_2038_problem).
   
   Negative time is never used in NuttX.  Negative time could arise in applications as a consequence of arithmetic operations, but that would be a non-portable behavior of the application because POSIX permits unsigned time_t.  For portability, applications should always cast to an appropriate time before performing signed operations.
   
   With unsigned time_t, the range is doubled.  Instead of 2038 (1970 + 68) then it should overflow at (1970 + 2*68) = 2,206.  Prior to that date, the upper 32-bits of a 64-bit time_t will always be zero.  So a 64-bit is totally wasteful until then.  The effect is no just limited to time_t parameters, but to the size of all structures that include a time_t field.


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