Re: A patch for mktime.c and tz*.c.

[Paul Eggert <eggert@twinsun.com>]

   From: hjl@lucon.org (H.J. Lu)
   Date: Fri, 6 Nov 1998 18:20:23 -0800 (PST)

   FWIW, I discovered those mktime bugs with VSX-PCT. It failed
   with GMT0BST. At lease, my change passes VSX-PCT.

I understand that glibc 2.0.100 passes the test cases.  (I haven't run
them myself.)  So perhaps your concerns are moot.

   So __daylight indicates if DST was, is, or will be in effect
   at the given time.

But this is logically equivalent to saying ``DST is in effect at some
point in time''.  I.e. the ``given time'' has nothing to do with
__daylight.

   Does glibc 2 know the offset between SDT and DST at the given time?
   If the answer is no, there is a bug in glibc 2. If the answer is
   yes, which I believe is the case, I store the offset in __daylight
   and use it in mktime.

The patch that you sent does not behave the way that you describe.
E.g. the patch has __tzfile_read set __daylight.  But this action
occurs rarely, only at the start of the program, and after TZ changes;
it doesn't occur for each ``given time''.  So (in general) it will
disagree with the difference between standard time and DST at ``the
given time''.