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<p>Hi Paul, thanks for letting me know that I am on the right path choosing to make the change in writezone. <br>
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<p>Hi Ken, thanks for the link to RFC draft. <br>
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<p>I will probably truncate the start of a TZif file and it states the following in the draft:<br>
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<pre class="newpage" style="font-size: 13.3333px; margin-top: 0px; margin-bottom: 0px; break-before: page;">   When truncating the start of a TZif file, the service MUST supply in
   the version 2+ data a first transition time that is the start point
   of the truncation range.  As with untruncated TZif files, time type 0
   indicates local time immediately before the start point, and the time
   type of the first transition indicates local time thereafter.​<br></pre>
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<p>Does it mean I need to add a start point transition to version 2+, but not to the version 1?<br>
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<p>BR,<br>
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<p>Christopher Wong<br>
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<div id="divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" color="#000000" style="font-size:11pt"><b>From:</b> tz <tz-bounces@iana.org> on behalf of Ken Murchison <murch@fastmail.com><br>
<b>Sent:</b> Thursday, January 31, 2019 16:08<br>
<b>To:</b> tz@iana.org<br>
<b>Subject:</b> Re: [tz] zic option for including data from a certain year onward</font>
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<div class="moz-cite-prefix">On 1/31/19 10:04 AM, <a class="moz-txt-link-abbreviated" href="mailto:Paul.Koning@dell.com">
Paul.Koning@dell.com</a> wrote:<br>
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<div class="">On Jan 31, 2019, at 7:18 AM, Christopher Wong <<a href="mailto:christopher.wong@axis.com" class="">christopher.wong@axis.com</a>> wrote:</div>
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Hi,<br class="">
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I think the tzdb is very good with its history. However, I would like to minimize the size and has been looking into how to achieve that.<br class="">
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Will it be of any interest with an option in zic to include only data from a certain year onward?<br class="">
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What is the best way?<br class="">
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1.​ Remove the Rules and Zone entries not relevant for that year onward during the parsing. Tried this, but ended up with with some nasty warnings.<br class="">
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2. Make changes in writezone-function. Trying this now, but I am getting confused with types, omittype, typemap, and so on.<br class="">
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It would be good if someone that knows the code can give me some hints if this is the right place to make such a change.<br class="">
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BR,<br class="">
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Christopher Wong<br class="">
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<div class="">Yes, this is a very useful feature.  I did it years ago for an embedded system product.  The right answer is 2 -- a new command line switch in zic to specify the start year, and a simple change in writezone to omit writing data for transitions
 older than the start date.  You have to be a bit careful to make sure that the rule in effect AT the start date appears in the output, i.e., not just transitions that are later than the start date.</div>
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<p>To this point, truncation of TZif files is discussed here: <a href="https://tools.ietf.org/html/draft-murchison-tzdist-tzif-16#section-5.1">
https://tools.ietf.org/html/draft-murchison-tzdist-tzif-16#section-5.1</a></p>
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<pre class="moz-signature" cols="72">-- 
Ken Murchison
Cyrus Development Team
FastMail US LLC</pre>
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