Re: Global Warming - Forth as answer

From	anton@mips.complang.tuwien.ac.at (Anton Ertl)
Newsgroups	comp.lang.forth
Subject	Re: Global Warming - Forth as answer
Date	2013-05-17 12:41 +0000
Organization	Institut fuer Computersprachen, Technische Universitaet Wien
Message-ID	<2013May17.144130@mips.complang.tuwien.ac.at> (permalink)
References	(5 earlier) <kn08r4$nc$1@dont-email.me> <2013May15.172242@mips.complang.tuwien.ac.at> <kn0o96$u8u$1@dont-email.me> <2013May16.145356@mips.complang.tuwien.ac.at> <kn36qa$o4b$1@dont-email.me>

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rickman <gnuarm@gmail.com> writes:
>On 5/16/2013 8:53 AM, Anton Ertl wrote:
>> rickman<gnuarm@gmail.com>  writes:
>>> On 5/15/2013 11:22 AM, Anton Ertl wrote:
>>> How is OVER_+ reversible exactly?  You can recover the data you started
>>> with using OVER -, but is that really the same as saying it is
>>> reversible?
>>
>> Yes, that's the idea.  You can run the computation in forward or
>> reverse direction.
>
>But that is not running the computation in the reverse direction, that 
>is recovering the prior state of the machine by a new computation.

If you have hardware that supports reversible operations, there is no
difference; there is also no new computation.  OVER_+ is an operation
that when run forwards is equivalent to the sequence OVER + in Forth,
but you can run it backwards, and that does something like running
OVER_- forwards.

>So my final conclusion is that OVER_+ is not reversible unless it is 
>atomic and is actually the same as A <= A + B, not an OVER followed by a +.

You got it!

- anton
-- 
M. Anton Ertl  http://www.complang.tuwien.ac.at/anton/home.html
comp.lang.forth FAQs: http://www.complang.tuwien.ac.at/forth/faq/toc.html
     New standard: http://www.forth200x.org/forth200x.html
   EuroForth 2013: http://www.euroforth.org/ef13/

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Global Warming - Forth as answer visualforth@rocketmail.com - 2013-05-14 15:21 -0700
  Re: Global Warming - Forth as answer hughaguilar96@yahoo.com - 2013-05-14 18:40 -0700
    Re: Global Warming - Forth as answer Steve <nospam275@gmail.com> - 2013-05-14 21:00 -0700
      Re: Global Warming - Forth as answer visualforth@rocketmail.com - 2013-05-15 22:24 -0700
        Re: Global Warming - Forth as answer Steve <nospam275@gmail.com> - 2013-05-19 19:25 -0700
  Re: Global Warming - Forth as answer albert@spenarnc.xs4all.nl (Albert van der Horst) - 2013-05-15 10:05 +0000
    Re: Global Warming - Forth as answer anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-05-15 12:42 +0000
      Re: Global Warming - Forth as answer rickman <gnuarm@gmail.com> - 2013-05-15 10:56 -0400
        Re: Global Warming - Forth as answer anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-05-15 15:08 +0000
          Re: Global Warming - Forth as answer rickman <gnuarm@gmail.com> - 2013-05-15 11:19 -0400
            Re: Global Warming - Forth as answer anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-05-15 15:22 +0000
              Re: Global Warming - Forth as answer rickman <gnuarm@gmail.com> - 2013-05-15 15:42 -0400
                Re: Global Warming - Forth as answer visualforth@rocketmail.com - 2013-05-15 13:45 -0700
                Re: Global Warming - Forth as answer Bernd Paysan <bernd.paysan@gmx.de> - 2013-05-15 23:38 +0200
                Re: Global Warming - Forth as answer anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-05-16 12:53 +0000
                Re: Global Warming - Forth as answer rickman <gnuarm@gmail.com> - 2013-05-16 14:03 -0400
                Re: Global Warming - Forth as answer anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-05-17 12:41 +0000
        Re: Global Warming - Forth as answer albert@spenarnc.xs4all.nl (Albert van der Horst) - 2013-05-17 13:17 +0000
          Re: Global Warming - Forth as answer dirk.bruehl@usa.net - 2013-05-17 08:36 -0700
            Re: Global Warming - Forth as answer Steve <nospam275@gmail.com> - 2013-05-19 19:12 -0700
            Re: Global Warming - Forth as answer Steve <nospam275@gmail.com> - 2013-05-20 00:06 -0700
    Re: Global Warming - Forth as answer rickman <gnuarm@gmail.com> - 2013-05-15 10:47 -0400
      Re: Global Warming - Forth as answer albert@spenarnc.xs4all.nl (Albert van der Horst) - 2013-05-17 13:23 +0000
        Re: Global Warming - Forth as answer rickman <gnuarm@gmail.com> - 2013-05-17 09:59 -0400
    Re: Global Warming - Forth as answer Steve <nospam275@gmail.com> - 2013-05-19 18:56 -0700
  Re: Global Warming - Forth as answer oh2aun@gmail.com - 2013-05-22 00:50 -0700

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