[D-runtime] FPU in core.time

[Brad Roberts]

One of the checkins today made this a real problem.  Looking at the pull tester, many many of the failures are due to
this.  The most recent linux 32/64 trunk build also failed with a time related failure.


On 1/15/2012 9:00 PM, Martin Nowak wrote:
> There are some failing unittests in core.time.
> 
> core.time(1754):
>     unittest
>     {
>         immutable curr = TickDuration.currSystemTick;
>         TickDuration t1 = curr;
>         immutable t2 = curr + curr;
>         t1 *= 2;
>         assert(t1 == t2);
> 
>         t1 = curr;
>         t1 *= 2.0; //<- This relies on 80-bit arithmetic and might fail since it is done on SSE
>         assert(t1 == t2);
>     }
> 
> 
> core.time(1523):
>     {
>         enum unitsPerSec = convert!("seconds", units)(1);
> 
>         if(ticksPerSec >= unitsPerSec)
>             return TickDuration(cast(long)(length * (ticksPerSec / cast(real)unitsPerSec)));
>         else
>             return TickDuration(cast(long)(length / (unitsPerSec / cast(real)ticksPerSec)));
>     }
> 
> This fails it's unittest on my Windows machine due to limited precision from the double division.
> The separate branches were originally used with integer arithmetic but it seems to me that they
> are no longer needed since the calculation is done in floating point now.
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