File Timestamp format

[CEbbinghaus]

I have been umming and aahing about finding the right format to store timetsamps in, and would appreciate some input from the community.

These are the options under consideration:

Type	Unit	Precision	Max year
i64	nanoseconds	1ns	2262
u64	nanoseconds	1ns	2554
i64	100ns	100ns	31,197
u64	100ns	100ns	60,424

and I am in particular wondering between the two u64 variants. 100ns is extremely accurate, it is highly doubtful that single ns accuracy is required, however only tar (using posix extension) supports it making arx stand out a little more against Zip (with extension), 7z & RAR which all support 100ns.

However we do loose 58,000 years worth of time. It is likely that this will never be required, and we can always change it at a later point through a revision of the format (v2). But what does the community think?