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<p>Yeah, that's right, it was DECtape and my birthday is a month
after DATE75 (in February). I whipped up a program to decode the
DATE UUO and gave it some test parameters. For 12 bits, the
largest date comes out to 1/4/1975 (not March) and the last date
of DATE75 (15 bits up) is 2/1/2052.<br>
</p>
<p><font size="+1"><tt> 0 is 1964/1/1 Date 0</tt><tt><br>
</tt><tt> 1 is 1964/1/2 Next Day</tt><tt><br>
</tt><tt> 4095 is 1975/1/4 12 bits up</tt><tt><br>
</tt><tt> 4096 is 1975/1/5 13 bit field width</tt><tt><br>
</tt><tt> 21203 is 2020/12/31 Recent date</tt><tt><br>
</tt><tt> 32767 is 2052/2/1 15 bits up</tt><tt><br>
</tt><tt> 32768 is 2052/2/2 16 bit field width</tt></font><br>
</p>
<div class="moz-cite-prefix">The program is essentially a driver to
invoke the CURDAT macro (as a subroutine) which is from the
October 1988 Tops-10 monitor calls manual, section 22.21 DATE UUO
[CALLI 14], page 22-48.</div>
<div class="moz-cite-prefix">
<p>Maybe March of '75 was when all the SPR's got published...</p>
<p>On Tops-20, PA1050 doesn't check for any of this at all and
exceeds 15 bits. The decoding routines don't notice this (see
above).<br>
</p>
<p>Tops-10 programs could handle the issue by doing GETTAB's of
%CNDAY (Day of Month), %CNMON (Month of Year) and %CNYER (Year)
which are in 36 bit fields. PA1050 doesn't implement these, but
that's a treatable condition.<br>
</p>
<p>It remains to be seen what a real DATE UUO is going to do in 31
years. Hopefully the monitor won't fall over...<br>
</p>
</div>
<blockquote type="cite"
cite="mid:007901d6dfc6$93980320$bac80960$@com">
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<pre class="moz-quote-pre" wrap="">On 12/31/20 5:45 PM, Robert Armstrong wrote:</pre>
<pre class="moz-quote-pre" wrap="">
The DECtape directory format (on TOPS-10) used only 12 bits to store the date, and between 1964 and 1975 are 4096 days.
Actually as I remember the rollover was sometime in March 1975, not January.
The DATE75 patch squeezed out three extra bits in the directory structure to allow for 32,768 days since 1/1/64.
Bob
<blockquote type="cite"><hr width="100%" size="2"><pre class="moz-quote-pre" wrap="">On 12/31/20 4:23 PM, Thomas DeBellis wrote:
So I went spelunking and here is what DATE75 is all about.
Briefly, very early versions of Tops-10 could only handle dates between January 1st 1964 and January 4th 1975 ...
</pre></blockquote></pre>
</blockquote>
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