[HECnet] The new few centuries (or DATE75)

[Thomas DeBellis]

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.

         0 is 1964/1/1           Date 0
         1 is 1964/1/2           Next Day
         4095 is 1975/1/4        12 bits up
         4096 is 1975/1/5        13 bit field width
         21203 is 2020/12/31     Recent date
         32767 is 2052/2/1       15 bits up
         32768 is 2052/2/2       16 bit field width

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.

Maybe March of '75 was when all the SPR's got published...

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).

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.

It remains to be seen what a real DATE UUO is going to do in 31 years.  
Hopefully the monitor won't fall over...

> ------------------------------------------------------------------------
> On 12/31/20 5:45 PM, Robert Armstrong wrote:
>    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
>
>> ------------------------------------------------------------------------
>> 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 ...
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