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Date: Thu, 4 Feb 2016 13:27:40 -0200
From: Alba Pompeo <albapompeo@...il.com>
To: musl@...ts.openwall.com
Cc: Martin Maechler <maechler@...t.math.ethz.ch>
Subject: strptime() question
Hello musl.
I've built R on a musl system and "make check-all" fails because R
does not get correct timezone information from the system.
Here's the error -
http://pastebin.com/raw/32D3ngNZ
This would be correct,
> difftime(
+ as.POSIXct(c("1970-01-01 00:00:00", "1970-01-01 12:00:00"), tz="EST5EDT"),
+ as.POSIXct(c("1970-01-01 00:00:00", "1970-01-01 00:00:00"), tz="UTC"))
Time differences in hours
[1] 5 17
but my system gives 4 16 which would suggest that it thinks that
there is only 4 hours time difference between UTC and EST5EDT and
that is just wrong.
The above can be translated to this (slightly more low-level) R code which
is already somewhat close to the internal C code of R :
> t0 <- strptime("1970-01-01 00:00:00", "%Y-%m-%d %H:%M:%OS", tz="UTC")
> as.numeric(t0)
[1] 0
> t1 <- strptime("1970-01-01 00:00:00", "%Y-%m-%d %H:%M:%OS", tz="EST5EDT")
> as.numeric(t1)
[1] 18000
> 18000 / 3600
[1] 5
>
That's why its 5 hours.
R's strptime() is close to the C library strptime(), so think musl
specialists should have it easy to do the above from C and find out
why you get 4 hour instead of 5 hour difference.
I'm certain this isn't a problem with R and I think it's up to me to
ensure that your system's C library strptime() function returns the
correct numbers for the above example, but I can't understand why it
doesn't.
Can anyone help here?
Thanks a lot.
Ciao.
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