[tz] Adapting localtime.c

[Carsten Larsen]

On Oct 9, 2016, at 20:03, Guy Harris wrote:
> On Oct 8, 2016, at 12:46 PM, Carsten Larsen <cs at innolan.dk> wrote:
>
>> AmigaOS uses an Epoch of January 1, 1978, 00:00:00 instead of January 1, 1970, 00:00:00 UTC. Time zone is not specified.
>>
>> The Epoch difference is easy to calculate.
>
> As "January 1, 1978, 00:00:00" is, as per your private response, January 1, 1978, 00:00:00 *local* time, then if you want to implement a UNIX-compatible version of time(), you need to convert the AmigaOS time to UTC, and then add 252460800 to the result.
>
> localtime(), in all implementations for UN*X, expects a UN*X-style time value to be passed to it; the tz implementation was originally an implementation for UN*X, so that's what it expects.
>
> So if you want to implement a time() that produces a result that can be passed to the tzcode implementation of localtime(), you need to implement a UN*X-compatible time().
>

The patch solves the time() returns *local time epoch*, *epoch offset*,
problem.


diff --git a/localtime.c b/localtime.c
index 6c00c45..313f846 100644
--- a/localtime.c
+++ b/localtime.c
@@ -2259,10 +2259,22 @@ posix2time(time_t t)
   /* Convert from the underlying system's time_t to the ersatz time_tz,
      which is called 'time_t' in this file.  */

+// Epoch is January 1, 1978 instead of January 1, 1970
+#define LOCAL_EPOCH_OFFSET 252460800
+
   time_t
   time(time_t *p)
   {
+  long zone;
     time_t r = sys_time(0);
+
+#ifdef LOCAL_EPOCH_OFFSET
+  if(lcl_is_set) {
+    zone = (daylight == 0 ? timezone : altzone);
+    time = (time_t)(tv.tv_secs + LOCAL_EPOCH_OFFSET + zone);
+  }
+#endif
+
     if (p)
       *p = r;
     return r;


It is probably not general enough to be included in the tzcode but maybe
it can inspire others.

Thank you for helping me out.

Kind regard
Carsten Larsen