Rules for Asia/Tokyo and Asia/Karachi

Joachim Wieland joe at
Mon Aug 23 22:10:47 UTC 2010


I am trying to understand the database file format and have a question
regarding the rule definition of Asia/Tokyo and Asia/Karachi. Both
time zones seem to be valid but I cannot see that from their
definition in the database.

Let's look at Asia/Tokyo only, but Asia/Karachi is similar...

# Rule  NAME    FROM    TO  TYPE    IN  ON  AT  SAVE    LETTER/S
Rule    Japan   1948    only    -   May Sun>=1  2:00    1:00    D
Rule    Japan   1948    1951    -   Sep Sat>=8  2:00    0   S
Rule    Japan   1949    only    -   Apr Sun>=1  2:00    1:00    D
Rule    Japan   1950    1951    -   May Sun>=1  2:00    1:00    D

Zone    Asia/Tokyo  9:18:59 -   LMT 1887 Dec 31 15:00u
           9:00    -   JST 1896
           9:00    -   CJT 1938
           9:00    Japan   J%sT

So Asia/Tokyo references the ruleset "Japan" which is only defined for
the years 1948 - 1951. Wouldn't that mean that Asia/Tokyo is only
valid during those years? Especially, it references a substring with
"J%sT", where does this substring come from for any other year?

Thanks a lot,

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