Re: [patch] Default to --enable-libstdcxx-time=auto

[Jakub Jelinek <jakub at redhat dot com>]

On Fri, May 24, 2013 at 03:29:43PM +0100, Jonathan Wakely wrote:
> >> in the latter).  And there is no conversion in between the two.
> >>
> >> Perhaps I'd have to do something like:
> >>   return time_point(system_clock::now().time_since_epoch());
> >> ?  Can try that.
> >
> > Ah, but the duration can be different depending on macros.
> 
> You can convert between durations: with duration_cast:
> 
> return time_point(duration_cast<duration>(system_clock::now().time_since_epoch()));

Actually return time_point(system_clock::now().time_since_epoch());
seems to work too, there is a ctor for that:
        template<typename _Rep2, typename _Period2, typename = typename
               enable_if<treat_as_floating_point<rep>::value
                         || (ratio_divide<_Period2, period>::den == 1
                             && !treat_as_floating_point<_Rep2>::value)>::type>
          constexpr duration(const duration<_Rep2, _Period2>& __d)
          : __r(duration_cast<duration>(__d).count()) { }
I've tried a configuration where system_clock::now() used gettimeofday
and system_clock duration was in microseconds and steady_clock was
the non-steady one, but with nanoseconds resolution, and system_clock::now()
then contains
        call    gettimeofday
        movq    (%rsp), %rax
        imulq   $1000000, %rax, %rax
        addq    8(%rsp), %rax
(1000000 * tv.tv_sec + tv.tv_usec) and steady_clock::now()
        call    _ZNSt6chrono12system_clock3nowEv
        imulq   $1000, %rax, %rax
so it converts correctly.

So, adjusted patches attached, ok for trunk/4.8 if they pass
bootstrap/regtest?  Guess Rainer will need to on top of that adjust
Solaris baseline_symbols.txt files.

	Jakub

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