From: Wally W.    
   Subject: Re: 'Leap Second' to Be Added on New Year's Eve This Year   
       
   On Sun, 1 Jan 2017 16:12:27 -0600, Mark Lloyd wrote:   
       
   >On 01/01/2017 12:46 PM, Wally W. wrote:   
   >   
   >[snip]   
   >   
   >> As I understand it, NT time uses a signed integer and tops out at   
   >> 0x7FFFFFFFFFFFFFFF = in the year 30828   
   >>   
   >> Unhappily, no sources suggest using negative integers will allow   
   >> setting the timestamp before the year 1600.   
   >   
   >What is the resolution of this clock? You get hundreds of billions of    
   >years if you count seconds since 1970.   
       
   For Windows NT, GetSystemTimeAsFileTime is in 100s of nanonsconds   
   (tenths of microseconds) since 1/1/1600.   
       
   Doing the math:   
       
   0x7FFFFFFFFFFFFFFF = 9223372036854775807   
       
   So:   
       
   9223372036854775807 / 365.25 / 86400 / (1e7)   
    =  29,227   
       
   29,227 + 1600 =  30,827   
       
   That is close to 30,828.   
       
   My approximation for leap years is too crude for a span of 30,000+   
   years.   
       
   Unix tops out much later in the table at the link above.   
       
   If I want to use the same (really durable) hardware to retrieve my   
   backups in the year 292,000,000 AD, I should start using Linux now.   
       
   Actually, I would have liked to have started using Linux exclusively   
   years ago.    
       
       
   >1600 is a leap year, like 2000 and 2400. Maybe it has something to do    
   >with that.   
   >   
   >> Otherwise, timestamps could be set for any date in known history; as   
   >> in 4004 BC, which by some counts includes Day One.   
   >   
   >The PHP I use has a strange "hole", where you can't set (with mktime) a    
   >year in the range of 0-100*. IIRC earlier years can be set, but it's one    
   >off (it thinks there is a year 0). 4004 BC** would be specified as -4003.   
   >   
   >* - I think this is a "convenience" that made sense with a 32-bit time_t    
   >where it adds 2000 to 0-79 and 1900 to 80-100, both 0 and 100 become 2000.   
   >   
   >** - I try to use CE / BCE instead of AD / BC. The numbers are the same,    
   >and it avoids a particular assumption.   
   >   
   >[snip]   
       
      
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