Speaking of "the original ... work", how did this all get started,

anyway?

The ultimate impetus was the legislation that changed the start of U. S. Daylight Saving Time from the last Sunday in April to the first Sunday in April. The proximate impetus was a mod.std.unix discussion on the subject. I've attached some of the early electronic mail. By 1/11/86 the format looked much as it does today. The "hard part" not dealt with in the 1/13/86 "distribution" was the text-format-to-binary-format converter (today's zic). --ado

From ado Mon Jan 6 10:28:48 1986

To: cbosgd!mark

Subject: Daylight Savings Time

Cc: seismo!philabs!linus!encore!necis!geo

Status: O

Well, I'll admit that my first reaction to the idea of something on the order

of "/etc/dstcap" was a smiley face. But over the weekend I thought about the

matter some more. The result of the thinking was a sheet of paper with this

on it:

...

eastern:\

...

:st=EST:\

...

:dt=EDT:\

...

:os=-21000:\

...

Now regardless of the way the above information is encoded, the questions are:

Is there enough information present above to deal with the various

Daylight Saving Time schemes that currently exist? Would the information be

enough to deal with anything that US (or foreign) legislators are likely

to dream up? Or does one *really* need to have something on the order of

"/etc/dstinfo" (with a stack and arithmetic and such)?

--ado

...

From cbosgd!cbpavo.cbosgd.ATT.UUCP!mark Fri Jan 10 16:19:08 1986 remote from seismo

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Date: Fri, 10 Jan 86 15:04:20 est

From: seismo!cbpavo.cbosgd.ATT.UUCP!mark (Mark Horton)

Message-Id: <8601102004.AA03218@cbpavo.cbosgd.ATT.UUCP>

To: elsie!ado, harvard!encore!encore!necis!geo

Subject: Re: Daylight Savings Time

While I like your semantics, the format is horrible. I'd much

prefer to see each year (or year range) in one place rather

than have it scattered over 14 different days of the week.

The format has to be something the average non-guru can understand.

Termcap is a bit much for such people. Something easy like

Year Key Parm Time GMT offset

1970 3-sun 4 0200 -0400

1970 3-sun 10 0200 -0500

1971 3-sun 4 0200 -0400

1971 3-sun 10 0200 -0500

1972 3-sun 4 0200 -0400

1972 3-sun 10 0200 -0500

1973 3-sun 4 0200 -0400

1973 3-sun 10 0200 -0500

1974 julian 120 0200 -0400

1974 julian 306 0200 -0500

1975 julian 0 0200 -0400

1975 julian 366 0200 -0500

1976 3-sun 4 0200 -0400

1976 3-sun 10 0200 -0500

This could probably be translated into a handy binary format for ctime

to use quickly. The parm is either the month number (for things like

"3rd Sunday") or the Julian date on which to make the change. The

above numbers are probably all wrong but you get the idea. You could

have any number of changes in a year, although 2 would be common.

Mark

From ado Sat Jan 11 12:42:16 1986

To: cbosgd!mark

Subject: DST

Status: O

An alternate approach to allow for multiple time zones. Make the rules look

like:

Rule Year(s) Month Day Time ST offset String

MostUS -1973 Apr last-Sun 2:00 1:00 D

MostUS -1973 Oct last-Sun 2:00 0 S

MostUS 1974 Jan last-Sun 2:00 1:00 D

MostUS 1974 Nov last-Sun 2:00 0 S

MostUS 1975 Feb last-Sun 2:00 1:00 D

MostUS 1975 Oct last-Sun 2:00 0 S

MostUS 1976- Apr last-Sun 2:00 1:00 D

MostUS 1976- Oct last-Sun 2:00 0 S

Patron 1969- Apr last-Sun 2:00 1:00 D

Patron 1969- Jul last-Sun 2:00 2:00 DD

Patron 1969- Aug last-Sun 2:00 1:00 D

Patron 1969- Oct last-Sun 2:00 0 S

and the Time Zone information look like

Name GMT offset Rule Abbreviation

Eastern -5:00 MostUS E%sT

Central -6:00 MostUS C%sT

Pacific -8:00 MostUS P%sT

Alaskan ? MostUS A%sT

Hawaiian ? MostUS H%sT

Patronian ? Patron P%sT

--ado

From ado Mon Jan 13 21:04:01 1986

To: cbosgd!mark

Subject: The easy part of ctime()

Status: O

The next letter from me should be a shell archive containing five files:

Makefile

timezone.h

ctime.c

try.c

fake.c

The important files are "timezone.h" which gives the format of "binary time

zone information files," and "ctime.c" which makes use of the files. . .

==============================================================