[tz] Adapting localtime.c

[Random832]

On Sat, Oct 8, 2016, at 15:46, Carsten Larsen wrote:
> The actual time is is number of seconds since 1.1.1978 and possibly a
> GMT offset (if the user have bothered to set it. The system does not 
> take it into consideration). There is no concept of daylight saving 
> rules and no concept of UTC.

So does AmigaOS not ship with a standard C library with its own time.h
functions? Even if they only handle one system-defined timezone, seeing
which of localtime/gmtime gives 1978-01-01 00:00:00 when you pass in a
value of 0 would be useful.

> I guess I need to determine the exact point of January 1, 1970, 
> 00:00:00 *UTC* on my (AmigaOS) timeline in order to use the time.h 
> functions in tz, and I assume the TZ variable and tz code can help me 
> to do so. Right ?

You need to figure out how the system's native functions handle it.

Also http://distributed.amiga.org/misc/timezone.text may be useful.
Maybe look at what this "ixemul" thing does. The version at
http://www.nic.funet.fi/index/gnu/funet/historical-funet-gnu-area-from-early-1990s/amiga/beta/
appears to treat it as UTC - from gettimeofday.c:

      __time_req->tr_node.io_Command = TR_GETSYSTIME;
      omask = syscall (SYS_sigsetmask, ~0);
      DoIO((struct IORequest *)__time_req);
      syscall (SYS_sigsetmask, omask);
      *tp = __time_req->tr_time;
      /* add the offset from unix to amigados time system */
      tp->tv_sec += (8*365+2) * 24 * 3600;