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8ef3e22719
Use sync::one::Once to fetch the mach_timebase_info only once when running precise_time_ns(). This helps because mach_timebase_info() is surprisingly inefficient. Also fix the order of operations when applying the timebase to the mach absolute time value. This improves the time on my machine from ``` test tests::bench_precise_time_ns ... bench: 157 ns/iter (+/- 4) ``` to ``` test tests::bench_precise_time_ns ... bench: 38 ns/iter (+/- 3) ``` and it will get even faster once #14174 lands.