[MLton] Problem with recent implementation of gettimeofday() on MinGW

[Wesley W. Terpstra]

On Tue, Jul 21, 2009 at 3:01 PM, Nicolas Bertolotti <
Nicolas.Bertolotti at mathworks.fr> wrote:

>  I have a binary which ran for 12783 seconds and calls Time.now() once at
> the beginning of its execution and once at the end of its execution.
>
>
>
> I could not identify the exact location of the overflow by looking at the
> code. I suspect the instruction:
>
> nowMicroSeconds.QuadPart +=
>
>                 1000000 * deltaCounter.QuadPart / frequency.QuadPart;
>
> But, in my point of view, it could only lead to a failure if the call
> occurs after (0xFFFFFFFFFFFFFFFFULL / 10000ULL) / 0xA6E78230ULL = 658767
> seconds.
>
Actually, it would be 2^63/10^6/0xa6e78230 = 3294 seconds. That corresponds
to what you saw. I'll note that your clock's frequency is significantly
higher than mine!

My patch uses a double there now which definitely has enough precision. Even
with your faster clock rate, the QueryPerformanceCounter won't wrap around
for 209 years, so the overly anal check comparing the high resolution timer
to the low resolution timer is unnecessary... Still, perhaps other systems
have an even faster clock.
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