On Fri, 2 Oct 1998, Markus Kuhn wrote:
Dave Flater wrote on 1998-09-21 18:57 UTC:
Other things that are not "broken" but that you might want to do:
* Add an explicit interval type, an extended difftime function that takes two xtimes and returns an interval, and the other obvious operations. I defined a bunch of operations over timestamps and intervals in C++ for XTide 2.0 but for C you probably want to keep it simple.
These are indeed rather simple to add, but what would be their semantics in the presence of leap seconds?
Taking a difference between two times, or adding one to a time, would need a parameter to give the clock type; if this is TIME_UTC and the implementation cannot determine whether there was a leap second in the relevant interval an error would need to be signalled. Note that a basic design principle is (should be) that leap seconds should not need to feature directly in code using the library: programs should need only be careful to use the correct clock types (which for time differences will often be TIME_MONOTONIC) and degrade gracefully on systems which have no leap second table or no time synchronisation. -- Joseph S. Myers jsm28@cam.ac.uk