Re: Y2K ProDOS 8 (2.0.3)

[jim symolon <jsymolon01@SPAMattbiBAIT.com>]

Charlie wrote:
> "Bill Garber" <willy46pa@comcast.net> wrote in message
> K-qdnUTUh5DObZOiXTWJgQ@comcast.com">news:K-qdnUTUh5DObZOiXTWJgQ@comcast.com...
>
> > "Charlie" <charlied@NOSPAMbboard.com> wrote in message
> > bel7pd01nou@enews2.newsguy.com">news:bel7pd01nou@enews2.newsguy.com...
> >
> > > "Michael J. Mahon" <mjmahon@aol.com> wrote in message
> > > 257d7207.0307101716.1ea07009@posting.google.com">news:257d7207.0307101716.1ea07009@posting.google.com...
> > >
> > > > "Michael Pender" <mpender@hotmail.com> wrote in message
> > >
> > > news:<x49Pa.71588$n%5.56799@nwrddc02.gnilink.net>...
> > >
> > > > > Michael J. Mahon <mjmahon@aol.com> wrote in message
> > > > > 20030710024051.00221.00000126@mb-m03.aol.com">news:20030710024051.00221.00000126@mb-m03.aol.com...
> > > > >
> > > > > > But Apple chose to go a different route, with year values from
> > > > > > 40-99 meaning 1940-1999 and years from 00-39 meaning
> > > > > > 2000-2039.  Relatively little software actually implements
> > > > > > this fold point, but having the definition out there certainly
> > > > > > biases the argument!
> > > > >
> > > > > ...snip...
> > > I believe all the file creation and mod fields (date and time) take up
> >
> > four
> >
> > > bytes which contain 5 unused bits (although they are in the field used for
> > > time).  Using those 5 bits in conjunction with the 7 bits already
> >
> > allocated
> >
> > > would have allowed 4096 years.  Why this wasn't done originally is a
> >
> > mystery to
> >
> > > me.
> >
> > I would assume that it is because Apple didn't think anyone would still
> > be using/caring about the Apple II computers for this long. ;-)
>
>
> I suppose you are right, Bill, At least about Apple the company but it is hard
> to understand why the people who actually did the programming would waste five
> bits on every file that was ever created in ProDOS while at the same time
> skimping on the number of bits used for the year field.
>
> Charlie

Actually the layout makes sense. I'll refer to the Beneath Apple ProDOS 
as a reference.

Directory Headers:
$1C:Creation Date = YYYYYYYM MMMDDDDD
$1E:Creation Time = 000HHHHH 00MMMMMM

Try to manipulate the fields in 6502 and you'll see why.  It's easier to
do this:
	LDY  #DATE
	LDA  (HDR),Y
	AND  #YEARMASK
	LSR  #YEARSHIFT
	; A = year

than to manipulate a 32-bit word when extracting or setting date time.

Using a "window" format is used in a lot of places, MS Access and Oracle 
to name a few.

Jim
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