[Rd] POSIXt oddness at end of 1969

[William Dunlap]

A user here noticed the following difference between Linux and Windows versions
of R-2.15.3 (and R-3.0.0, I think) when using times within a second of the end of 1969:

f <- function (sec = -1) 
{
    x1 <- as.POSIXct(c(2 * sec, sec, 0), origin = "1970-01-01",  tz = "UTC")
    x2 <- as.POSIXlt(x1)
    x3 <- as.POSIXct(x2, origin = "1970-01-01", tz = "UTC")
    list(x1 = x1, x2 = x2, x3 = x3)
}

On Windows I get:
  > f(-1)
  $x1
  [1] "1969-12-31 23:59:58 UTC"
  [2] "1969-12-31 23:59:59 UTC"
  [3] "1970-01-01 00:00:00 UTC"

  $x2
  [1] "1969-12-31 23:59:58 UTC"
  [2] "1969-12-31 23:59:59 UTC"
  [3] "1970-01-01 00:00:00 UTC"
  
  $x3
  [1] "1969-12-31 23:59:58 UTC"
  [2] "1969-12-31 23:59:59 UTC"
  [3] "1970-01-01 00:00:00 UTC"

On Linux I get an NA in x3 for 1 second before 1970:
  > f(-1)
  $x1
  [1] "1969-12-31 23:59:58 UTC"
  [2] "1969-12-31 23:59:59 UTC"
  [3] "1970-01-01 00:00:00 UTC"
  
  $x2
  [1] "1969-12-31 23:59:58 UTC"
  [2] "1969-12-31 23:59:59 UTC"
  [3] "1970-01-01 00:00:00 UTC"
  
  $x3
  [1] "1969-12-31 23:59:58 UTC"
  [2] NA
  [3] "1970-01-01 00:00:00 UTC"

On Windows, sessionInfo() is
  R version 2.15.3 (2013-03-01)
  Platform: x86_64-w64-mingw32/x64 (64-bit)
  
  locale:
  [1] LC_COLLATE=English_United States.1252  LC_CTYPE=English_United States.1252   
  [3] LC_MONETARY=English_United States.1252 LC_NUMERIC=C                          
  [5] LC_TIME=English_United States.1252    
  
  attached base packages:
  [1] stats     graphics  grDevices utils     datasets  methods   base     

On Linux,  sessionInfo() is
  > sessionInfo()
  R version 2.15.3 (2013-03-01)
  Platform: x86_64-unknown-linux-gnu (64-bit)
  
  locale:
   [1] LC_CTYPE=en_US.UTF-8       LC_NUMERIC=C               LC_TIME=en_US.UTF-8
   [4] LC_COLLATE=en_US.UTF-8     LC_MONETARY=en_US.UTF-8    LC_MESSAGES=en_US.UTF-8
   [7] LC_PAPER=C                 LC_NAME=C                  LC_ADDRESS=C
  [10] LC_TELEPHONE=C             LC_MEASUREMENT=en_US.UTF-8 LC_IDENTIFICATION=C

  attached base packages:
  [1] stats     graphics  grDevices utils     datasets  methods   base

Bill Dunlap
Spotfire, TIBCO Software
wdunlap tibco.com