| 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 (by default), 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=2022a | |
| for the appropriate version. If zic is not on the path, use something like | |
| make -f Make.zi VERSION=2022a 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. In 2021 it was possible to use macOS, whose zic gave | |
| many warnings and created a ca 475KB file. | |
| Note that we include 'backward': vendor versions might not, or might | |
| use 'backzone'. |