Re: Algorithm to exploit 32 bit time functions to do time zone calculations

Michael G Schwern dixit:

>>> Maybe you can shed some light on this problem, what to do about year 0?
>>=20
>> I actually haven=E2=80=99t thought about year 0, since localtime/mktime =
do that,
>> and mjd2tm and tm2mjd from DJB code. I think it=E2=80=99s illegal, isn=
=E2=80=99t it?
>
>Illegal according to who?
>
>C99 and POSIX 1003.1 define tm.tm_year as a signed int with a range of "ye=
ars
>since 1900" which makes a negative year perfectly "legal".

0 is not negative, and there has been no year 0, only 1 ante christo (-1)
followed directly by 1 post christo. (Ironically, he was probably not born
by then.)

>I'm a little lost.  Could you give an example?

Yup. Convert -2=E2=81=B6=C2=B3 from time_t to TAI (while honouring leap sec=
onds), and
it will wrap, because the result would be -2=E2=81=B6=C2=B3-10 (plus the BI=
AS), which
is actually positive. But that doesn=E2=80=99t matter, as it wraps back on =
the
way back. So don=E2=80=99t introduce any arbitrary limits.

>I wonder how a Chinese locale deals with this.  They switched from Julian =
to
>Gregorian after 1901, so it should show up in any Chinese localtime()
>implementation.  Also Russia and much of Eastern Europe.

I think a =E2=80=9Cstruct tm=E2=80=9D is just always gregorian, since other=
 calendars
do not neccessarily have the same day/month/year concept (example:
Japanese).

>PPS  How does one get the damn qsecretary program to stop making you confi=
rm
>every email to this list?  I'm already subscribed.

Same problem here. I think it uses the envelope address, not the header
address, to check, which is, IMO, a bug in DJB=E2=80=99s mailing list softw=
are =E2=98=BA

bye,
//mirabilos
--=20
Sometimes they [people] care too much: pretty printers [and syntax highligh=
-
ting, d.A.] mechanically produce pretty output that accentuates irrelevant
detail in the program, which is as sensible as putting all the prepositions
in English text in bold font.=09-- Rob Pike in "Notes on Programming in C"