Large timecounter delta handling

Hello,

I synchronize currently the port of the FreeBSD timecounters to RTEMS. I 
have to write test cases for all code we use in RTEMS. In 2020 some code 
was added to fix integer overflow issues with large time deltas while 
getting the time from a timehand.

https://github.com/freebsd/freebsd-src/commit/6cf2362e2c7e9061611f93a48ec654a5b7451d6b#diff-8b8e2f8e41e6a847f14ab08c7d50454c20a4a135f2c2241d91687c0832c1d99e

If a time delta obtained by tc_delta(th) is greater than or equal to 
th->th_large_delta, then some extra calculation is carried out.

The th->th_large_delta is computed like this

	scale = (uint64_t)1 << 63;
	scale += (th->th_adjustment / 1024) * 2199;
	scale /= th->th_counter->tc_frequency;
	th->th_scale = scale * 2;
	th->th_large_delta = MIN(((uint64_t)1 << 63) / scale, UINT_MAX);

If we ignore the th->th_adjustment (== 0), then we have ideally

scale = 2**64 / f
th->th_large_delta = MIN( f / 2, UINT_MAX )

Does this mean that we only need the large delta processing if a 
timehand was not updated for about 0.5s?

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