[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [Scheme-reports] TAI epoch


In my formal comment, I noted that:

"The current-second procedure in the sixth draft of the R7RS returns the number
of TAI seconds since 1970-01-01 00:00:10 TAI. This epoch corresponds
approximately to the Unix and POSIX epoch of 1970-01-01 00:00:00 UTC.”

Note the word “approximately”. This is because TAI and UTC seconds were not the same prior to 1972, and as a consequence of this, as Shiro has pointed out, the difference between TAI and UTC was not constant prior to 1972 even in the absence of leap seconds. For the purpose of my formal comment, it would have been a distraction to get into the details. So, I was aware of this issue, and should have caught it in the final draft. Sorry about that.

Alex notes that my implementation of a procedure to return the difference between TAI and UTC fails prior to 1972. This is because I was mainly interested in converting the result of clock() et al. to TAI, and in the absence of a time machine, there is not much need for this prior to 1972. If I get a chance in the next few weeks, I’ll fix this, at least to 1970. As you go further into the past, the difference between atomic time (TAI and its predecessors) and astronomical time (UTC and its predecessors) becomes more uncertain, so I’ll have to think about how far back it makes sense to continue this.



Scheme-reports mailing list