The R Project SVN R

localtime.c is a stripped-down version of that from tzcode, from

http://www.iana.org/time-zones, converted to use a 64-bit time_t on

all platforms.  Apart from removing unused code and merging in the

parts of private.h which are needed, the other main changes are

- to use environment variable TZDIR to point to the zoneinfo files, and

  failing that, R_HOME/share/zoneinfo.

- to call getTZinfo() to get the default timezone if TZ is unset.

strftime.c is a stripped-down version of that from tzcode, using the

system version for locale-dependent day/month/am/pm names.

zoneinfo.zip is formed by installing tzdata on a system with zic, and

zipping up the results, after adding a file VERSION giving the

version.  (The binary databases are byte streams, and so do not depend

on the architecture.  There are some comments about whether time_t is

signed, which it is on all sensible platforms.  This is only used with

R's implemntation, where time_t is int_fast64_t, hence signed.)

To remake it, download the current version of tzdataXXXXx.tar.gz from

https://www.iana.org/time-zones to this directory and run

make -f Make.zi VERSION=2019c

for the appropriate version.  If zic is not on the path, use something like

make -f Make.zi VERSION=2019c ZIC=/usr/sbin/zic

NB: it seems that this needs to be done on a system with 64-bit time_t

or the catalogs will be confined to 1902-2038.  (Even that did not

suffice on earlier versions of macOS.)  As a sanity check, the size of

zoneinfo.zip should be about 410KB if 64-bit: a 32-bit version will be

about 280KB.