[gpsd-commit-watch] [SCM] GPSD branch, master, updated. release-3.16-535-ga5bbf14

[Fred Wright]

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- Log -----------------------------------------------------------------
commit a5bbf14516aa7d0650e240806f39b98442768e94
Author: Fred Wright <address@hidden>
Date:   Fri Jan 6 23:04:46 2017 -0800

    Removes pointless OSX-specific clock_gettime fallback.
    
    The clock_gettime() fallback code was using clock_get_time() on OSX,
    presumably in order to get its apparent nanosecond resolution.  But it
    turns out that clock_get_time() only has microsecond resolution, in
    spite of the nanosecond-resolution data format.  This makes it no
    better than gettimeofday() in practice.  In addition, it's
    substantially slower.  The clock_get_time() version as typically
    implemented (including here) takes about 3us on a 3GHz Mac Pro, as
    compared to about 43ns for gettimeofday().  Even if the code is
    improved by cacheing the clock port rather than obtaining it once per
    call, it still takes over 800us.  Thus, using gettimeofday() and
    scaling the microseconds to nanoseconds is actually the best approach.
    
    Since there was already a fallback based on gettimeofday() for other
    clock_gettime()-impaired platforms, this fix simply removes the
    OSX-specific version and the related conditional.
    
    It's worth noting that the official OSX clock_gettime(), which
    appeared on 10.12 (Sierra), still has only microsecond resolution, and
    comparable speed to gettimeofday().
    
    The gettimeofday()-based fallback included some "paranoid" code
    checking for out-of-range microsecond values.  But in addition to its
    being questionable to check the direct return results of system calls,
    the "paranoid" checks were *after* the tv_usec value had already been
    used.  Hence, that code never could have had any effect, and would
    have been optimized out by a clever compiler.  It's now been removed.
    
    TESTED:
    Ran "scons build-all check" on OSX 10.5, 10.9, and 10.12, as well as
    Ubuntu 14.

-----------------------------------------------------------------------

Summary of changes:
 clock_gettime.c |   36 ++++++++++--------------------------
 1 file changed, 10 insertions(+), 26 deletions(-)


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