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Re: unexpected +LOOP behavior

From anton@mips.complang.tuwien.ac.at (Anton Ertl)
Newsgroups comp.lang.forth
Subject Re: unexpected +LOOP behavior
Date 2015-05-24 15:44 +0000
Organization Institut fuer Computersprachen, Technische Universitaet Wien
Message-ID <2015May24.174418@mips.complang.tuwien.ac.at> (permalink)
References (1 earlier) <c8aab894-c934-4f43-b87c-4d5c57ffd5c7@googlegroups.com> <1a315aac-9a17-4645-89f5-5baac403d4b3@googlegroups.com> <ad6f02c3-4081-46b9-8b9a-ca5c321f7c55@googlegroups.com> <mjso0v$apk$2@dont-email.me> <9bca4add-f007-4853-835e-78d0c964d48a@googlegroups.com>

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Michael Barry <barrym95838@yahoo.com> writes:
>On Sunday, May 24, 2015 at 7:43:50 AM UTC-7, rickman wrote:
>> Could you explain this to a newbie?  With V-flag (I assume that means 
>> overflow?) optimization is the count being done over a range other than 
>> the values expected for I?
>> 
>
>I'll try, but I can't guarantee that I'll make sense.
>
>The idea with twos complement machines is that V will set if an add
> instruction causes the value to cross the border between the largest
> positive integer and the largest negative integer, or vice-versa.
> On a 16-bit machine (which I will continue to use in this example)
> that border is between $7fff and $8000.  The trick comes from "fudge-
> factoring" your index so that the limit and that border coincide.
>
>In (DO) instead of saving the index and limit on the Rstack, you
> instead save the fudge-factor (which is $8000-limit) and your
> fudged index (which is index+fudge).  (LOOP) and (+LOOP) now only
> have to update and check the V flag to see if they're done, but I
> and J have to be modified to "un-fudge" the index values, using
> the saved fudge-factor.  I'm not convinced that it's a great idea,
> but it happens to be the easiest way to duplicate the odd behavior
> that the OP described, making it something like a case of "the
> tail wagging the dog" for this little gem.

One can also do the fudging in LOOP/+LOOP, and avoid the unfudging in
I.  Something like, for (+LOOP):

x=index-limit+$8000 \ one lea on 386
y=x+n
if overflow
  ... loop ends ...
else
index = index+n
jump to the loop start

This will be slower on the all important empty do-loop benchmark, but
probably faster if there is more than one I per iteration.

But a /LOOP that counts only upwards and a \LOOP (called -LOOP in
Gforth) that counts only downwards are more efficient yet.

- 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 2015: http://www.mpeforth.com/euroforth2015/euroforth2015.htm

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unexpected +LOOP behavior chitselb <chitselb@gmail.com> - 2015-05-23 19:27 -0700
  Re: unexpected +LOOP behavior hughaguilar96@gmail.com - 2015-05-23 20:27 -0700
    Re: unexpected +LOOP behavior Hans Bezemer <the.beez.speaks@gmail.com> - 2015-05-24 13:44 +0200
      Re: unexpected +LOOP behavior rickman <gnuarm@gmail.com> - 2015-05-24 10:36 -0400
        Re: unexpected +LOOP behavior Hans Bezemer <the.beez.speaks@gmail.com> - 2015-05-24 23:16 +0200
          Re: unexpected +LOOP behavior hughaguilar96@gmail.com - 2015-05-24 15:57 -0700
          Re: unexpected +LOOP behavior Bernd Paysan <bernd.paysan@gmx.de> - 2015-05-25 02:21 +0200
            Re: unexpected +LOOP behavior "Elizabeth D. Rather" <erather@forth.com> - 2015-05-24 15:21 -1000
              Re: unexpected +LOOP behavior hughaguilar96@gmail.com - 2015-05-24 19:49 -0700
            Re: unexpected +LOOP behavior hughaguilar96@gmail.com - 2015-05-24 18:22 -0700
            Re: unexpected +LOOP behavior "WJ" <w_a_x_man@yahoo.com> - 2015-05-26 17:20 +0000
              Re: unexpected +LOOP behavior rickman <gnuarm@gmail.com> - 2015-05-26 14:15 -0400
                Re: unexpected +LOOP behavior "Elizabeth D. Rather" <erather@forth.com> - 2015-05-26 08:37 -1000
                Re: unexpected +LOOP behavior rickman <gnuarm@gmail.com> - 2015-05-26 15:09 -0400
                Re: unexpected +LOOP behavior "Elizabeth D. Rather" <erather@forth.com> - 2015-05-26 09:19 -1000
                Re: unexpected +LOOP behavior rickman <gnuarm@gmail.com> - 2015-05-26 17:08 -0400
                Re: unexpected +LOOP behavior chitselb <chitselb@gmail.com> - 2015-05-26 15:42 -0700
                Re: unexpected +LOOP behavior rickman <gnuarm@gmail.com> - 2015-05-26 19:30 -0400
                Re: unexpected +LOOP behavior chitselb <chitselb@gmail.com> - 2015-05-26 17:45 -0700
                Re: unexpected +LOOP behavior rickman <gnuarm@gmail.com> - 2015-05-26 21:33 -0400
                Re: unexpected +LOOP behavior Coos Haak <chforth@hccnet.nl> - 2015-05-27 14:08 +0200
                Re: unexpected +LOOP behavior chitselb <chitselb@gmail.com> - 2015-05-27 06:32 -0700
                Re: unexpected +LOOP behavior Coos Haak <chforth@hccnet.nl> - 2015-05-27 16:15 +0200
                Re: unexpected +LOOP behavior "Elizabeth D. Rather" <erather@forth.com> - 2015-05-26 14:32 -1000
                Re: unexpected +LOOP behavior anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-05-27 08:30 +0000
                Re: unexpected +LOOP behavior rickman <gnuarm@gmail.com> - 2015-05-27 17:15 -0400
                Re: unexpected +LOOP behavior hughaguilar96@gmail.com - 2015-05-29 21:05 -0700
          Re: unexpected +LOOP behavior rickman <gnuarm@gmail.com> - 2015-05-25 01:41 -0400
            Re: unexpected +LOOP behavior Raimond Dragomir <raimond.dragomir@gmail.com> - 2015-05-24 23:26 -0700
              Re: unexpected +LOOP behavior anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-05-25 14:33 +0000
              Re: unexpected +LOOP behavior rickman <gnuarm@gmail.com> - 2015-05-25 10:56 -0400
                Re: unexpected +LOOP behavior Raimond Dragomir <raimond.dragomir@gmail.com> - 2015-05-25 11:28 -0700
                Re: unexpected +LOOP behavior rickman <gnuarm@gmail.com> - 2015-05-25 14:33 -0400
                Re: unexpected +LOOP behavior hughaguilar96@gmail.com - 2015-05-25 12:57 -0700
                Re: unexpected +LOOP behavior humptydumpty <ouatubi@gmail.com> - 2015-05-25 23:01 -0700
          Re: unexpected +LOOP behavior anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-05-25 14:21 +0000
          Re: unexpected +LOOP behavior albert@spenarnc.xs4all.nl (Albert van der Horst) - 2015-05-26 23:59 +0000
          Re: unexpected +LOOP behavior anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-05-27 09:15 +0000
            Re: unexpected +LOOP behavior anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-05-27 10:06 +0000
            Re: unexpected +LOOP behavior rickman <gnuarm@gmail.com> - 2015-05-27 12:03 -0400
              Re: unexpected +LOOP behavior anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-05-27 16:23 +0000
                Re: unexpected +LOOP behavior rickman <gnuarm@gmail.com> - 2015-05-27 12:39 -0400
            Re: unexpected +LOOP behavior Hans Bezemer <the.beez.speaks@gmail.com> - 2015-05-27 22:14 +0200
              Re: unexpected +LOOP behavior rickman <gnuarm@gmail.com> - 2015-05-27 17:13 -0400
                Re: unexpected +LOOP behavior Hans Bezemer <the.beez.speaks@gmail.com> - 2015-05-27 23:36 +0200
                Re: unexpected +LOOP behavior rickman <gnuarm@gmail.com> - 2015-05-27 18:06 -0400
                Re: unexpected +LOOP behavior Hans Bezemer <the.beez.speaks@gmail.com> - 2015-05-29 10:35 +0200
                Re: unexpected +LOOP behavior "Alex McDonald" <blog@rivadpm.com> - 2015-05-29 12:16 +0100
                Re: unexpected +LOOP behavior rickman <gnuarm@gmail.com> - 2015-05-29 09:42 -0400
                Re: unexpected +LOOP behavior Hans Bezemer <the.beez.speaks@gmail.com> - 2015-05-29 16:16 +0200
                Re: unexpected +LOOP behavior "Alex McDonald" <blog@rivadpm.com> - 2015-05-29 15:24 +0100
              Re: unexpected +LOOP behavior "Rod Pemberton" <fork@lllljunkqwer.cpm> - 2015-05-27 17:32 -0400
                Re: unexpected +LOOP behavior Coos Haak <chforth@hccnet.nl> - 2015-05-27 23:59 +0200
                Re: unexpected +LOOP behavior rickman <gnuarm@gmail.com> - 2015-05-27 19:31 -0400
                Re: unexpected +LOOP behavior Raimond Dragomir <raimond.dragomir@gmail.com> - 2015-05-27 23:11 -0700
              Re: unexpected +LOOP behavior "Alex McDonald" <blog@rivadpm.com> - 2015-05-28 12:21 +0100
                Re: unexpected +LOOP behavior "Alex McDonald" <blog@rivadpm.com> - 2015-05-28 12:24 +0100
                Re: unexpected +LOOP behavior Hans Bezemer <the.beez.speaks@gmail.com> - 2015-05-29 10:53 +0200
                Re: unexpected +LOOP behavior "Alex McDonald" <blog@rivadpm.com> - 2015-05-29 12:19 +0100
              Re: unexpected +LOOP behavior anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-05-29 13:51 +0000
                Re: unexpected +LOOP behavior Hans Bezemer <the.beez.speaks@gmail.com> - 2015-05-29 17:48 +0200
            Re: unexpected +LOOP behavior Bernd Paysan <bernd.paysan@gmx.de> - 2015-05-29 02:08 +0200
              Re: unexpected +LOOP behavior anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-05-29 08:25 +0000
                Re: unexpected +LOOP behavior "Alex McDonald" <blog@rivadpm.com> - 2015-05-29 12:40 +0100
                Re: unexpected +LOOP behavior anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-05-29 13:16 +0000
                Re: unexpected +LOOP behavior albert@spenarnc.xs4all.nl (Albert van der Horst) - 2015-05-29 18:43 +0000
                Re: unexpected +LOOP behavior "Alex McDonald" <blog@rivadpm.com> - 2015-05-29 20:08 +0100
                x86 tricks Lars Brinkhoff <lars.spam@nocrew.org> - 2015-06-05 09:42 +0200
                Re: x86 tricks albert@spenarnc.xs4all.nl (Albert van der Horst) - 2015-06-05 09:32 +0000
                Re: x86 tricks anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-06-05 09:40 +0000
                Re: x86 tricks albert@spenarnc.xs4all.nl (Albert van der Horst) - 2015-06-05 11:17 +0000
                Re: x86 tricks anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-06-05 15:49 +0000
                Re: x86 tricks "Alex McDonald" <blog@rivadpm.com> - 2015-06-05 17:45 +0100
                Re: x86 tricks anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-06-05 16:53 +0000
                Re: x86 tricks rickman <gnuarm@gmail.com> - 2015-06-07 13:20 -0400
                Re: x86 tricks anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-06-08 07:18 +0000
                Re: x86 tricks Bernd Paysan <bernd.paysan@gmx.de> - 2015-06-08 17:18 +0200
                Re: x86 tricks Tessa Bonting <tessa.bonting@gmail.com> - 2015-06-08 08:42 -0700
                Re: x86 tricks albert@spenarnc.xs4all.nl (Albert van der Horst) - 2015-06-06 09:47 +0000
                Re: x86 tricks anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-06-07 15:05 +0000
                Re: x86 tricks "Alex McDonald" <blog@rivadpm.com> - 2015-06-07 17:49 +0100
                Re: x86 tricks "Alex McDonald" <blog@rivadpm.com> - 2015-06-05 13:19 +0100
      Re: unexpected +LOOP behavior Mark Wills <markwills1970@gmail.com> - 2015-05-25 01:38 -0700
  Re: unexpected +LOOP behavior Michael Barry <barrym95838@yahoo.com> - 2015-05-23 21:33 -0700
    Re: unexpected +LOOP behavior hughaguilar96@gmail.com - 2015-05-23 22:10 -0700
      Re: unexpected +LOOP behavior chitselb <chitselb@gmail.com> - 2015-05-23 22:20 -0700
        Re: unexpected +LOOP behavior hughaguilar96@gmail.com - 2015-05-25 21:13 -0700
          Re: unexpected +LOOP behavior "Rod Pemberton" <fork@lllljunkqwer.cpm> - 2015-05-27 17:34 -0400
            Re: unexpected +LOOP behavior chitselb <chitselb@gmail.com> - 2015-05-27 22:04 -0700
              Re: unexpected +LOOP behavior rickman <gnuarm@gmail.com> - 2015-05-28 01:27 -0400
                Re: unexpected +LOOP behavior "Rod Pemberton" <fork@lllljunkqwer.cpm> - 2015-05-28 03:20 -0400
                Re: unexpected +LOOP behavior rickman <gnuarm@gmail.com> - 2015-05-28 04:13 -0400
                Re: unexpected +LOOP behavior "Rod Pemberton" <fork@lllljunkqwer.cpm> - 2015-05-29 04:23 -0400
                Re: unexpected +LOOP behavior rickman <gnuarm@gmail.com> - 2015-05-29 11:28 -0400
                Re: unexpected +LOOP behavior "Rod Pemberton" <fork@lllljunkqwer.cpm> - 2015-05-29 18:32 -0400
                Re: unexpected +LOOP behavior rickman <gnuarm@gmail.com> - 2015-05-29 18:53 -0400
      Re: unexpected +LOOP behavior Michael Barry <barrym95838@yahoo.com> - 2015-05-23 22:26 -0700
        Re: unexpected +LOOP behavior "Elizabeth D. Rather" <erather@forth.com> - 2015-05-23 21:37 -1000
          Re: unexpected +LOOP behavior hughaguilar96@gmail.com - 2015-05-24 10:24 -0700
            Re: unexpected +LOOP behavior "Rod Pemberton" <fork@lllljunkqwer.cpm> - 2015-05-24 20:40 -0400
            Re: unexpected +LOOP behavior Hans Bezemer <the.beez.speaks@gmail.com> - 2015-05-25 14:08 +0200
              Re: unexpected +LOOP behavior "Rod Pemberton" <fork@lllljunkqwer.cpm> - 2015-05-25 17:27 -0400
                Re: unexpected +LOOP behavior "Elizabeth D. Rather" <erather@forth.com> - 2015-05-25 14:47 -1000
                Re: unexpected +LOOP behavior "Rod Pemberton" <fork@lllljunkqwer.cpm> - 2015-05-27 17:33 -0400
            Re: unexpected +LOOP behavior Michael Barry <barrym95838@yahoo.com> - 2015-05-25 12:53 -0700
              Re: unexpected +LOOP behavior hughaguilar96@gmail.com - 2015-05-25 13:05 -0700
              Re: unexpected +LOOP behavior "Elizabeth D. Rather" <erather@forth.com> - 2015-05-25 14:49 -1000
                Re: unexpected +LOOP behavior Michael Barry <barrym95838@yahoo.com> - 2015-05-25 18:03 -0700
                Re: unexpected +LOOP behavior "Elizabeth D. Rather" <erather@forth.com> - 2015-05-25 16:44 -1000
                Re: unexpected +LOOP behavior humptydumpty <ouatubi@gmail.com> - 2015-05-25 22:56 -0700
                Re: unexpected +LOOP behavior anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-05-26 08:05 +0000
        Re: unexpected +LOOP behavior rickman <gnuarm@gmail.com> - 2015-05-24 10:43 -0400
          Re: unexpected +LOOP behavior Michael Barry <barrym95838@yahoo.com> - 2015-05-24 08:29 -0700
            Re: unexpected +LOOP behavior anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-05-24 15:44 +0000
              Re: unexpected +LOOP behavior Michael Barry <barrym95838@yahoo.com> - 2015-05-27 00:57 -0700
              Re: unexpected +LOOP behavior chitselb <chitselb@gmail.com> - 2015-06-05 13:11 -0700
                Re: unexpected +LOOP behavior "Elizabeth D. Rather" <erather@forth.com> - 2015-06-05 12:24 -1000
                Re: unexpected +LOOP behavior JennyB <jennybrien@googlemail.com> - 2015-06-06 13:29 -0700
                Re: unexpected +LOOP behavior anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-06-07 14:56 +0000
                Re: unexpected +LOOP behavior "Elizabeth D. Rather" <erather@forth.com> - 2015-06-07 10:38 -1000
                Re: unexpected +LOOP behavior anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-06-08 08:08 +0000
        Re: unexpected +LOOP behavior hughaguilar96@gmail.com - 2015-05-24 10:01 -0700
      Re: unexpected +LOOP behavior rickman <gnuarm@gmail.com> - 2015-05-24 10:40 -0400
        Re: unexpected +LOOP behavior hughaguilar96@gmail.com - 2015-05-24 11:29 -0700
          Re: unexpected +LOOP behavior "Alex McDonald" <blog@rivadpm.com> - 2015-05-25 09:51 -0700
            Re: unexpected +LOOP behavior hughaguilar96@gmail.com - 2015-05-25 10:44 -0700
              Re: unexpected +LOOP behavior "Alex McDonald" <blog@rivadpm.com> - 2015-05-25 12:34 -0700
                Re: unexpected +LOOP behavior hughaguilar96@gmail.com - 2015-05-25 12:59 -0700
  unexpected +LOOP behavior Mark Wills <markwills1970@gmail.com> - 2015-05-24 01:39 -0700
    Re: unexpected +LOOP behavior Coos Haak <chforth@hccnet.nl> - 2015-05-24 14:46 +0200
      Re: unexpected +LOOP behavior Mark Wills <markwills1970@gmail.com> - 2015-05-25 01:17 -0700
    Re: unexpected +LOOP behavior "Rod Pemberton" <fork@lllljunkqwer.cpm> - 2015-05-24 20:48 -0400
      Re: unexpected +LOOP behavior hughaguilar96@gmail.com - 2015-05-24 18:15 -0700
      Re: unexpected +LOOP behavior anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-05-25 12:35 +0000
        Re: unexpected +LOOP behavior "Rod Pemberton" <fork@lllljunkqwer.cpm> - 2015-05-25 17:27 -0400
          Re: unexpected +LOOP behavior rickman <gnuarm@gmail.com> - 2015-05-25 18:16 -0400
            Re: unexpected +LOOP behavior chitselb <chitselb@gmail.com> - 2015-05-25 16:17 -0700
              Re: unexpected +LOOP behavior chitselb <chitselb@gmail.com> - 2015-05-25 17:16 -0700
                Re: unexpected +LOOP behavior Michael Barry <barrym95838@yahoo.com> - 2015-05-25 17:50 -0700
                Re: unexpected +LOOP behavior chitselb <chitselb@gmail.com> - 2015-05-25 18:47 -0700
              Re: unexpected +LOOP behavior Michael Barry <barrym95838@yahoo.com> - 2015-05-25 20:01 -0700
                Re: unexpected +LOOP behavior chitselb <chitselb@gmail.com> - 2015-05-25 20:29 -0700
                Re: unexpected +LOOP behavior chitselb <chitselb@gmail.com> - 2015-05-25 20:32 -0700
              Re: unexpected +LOOP behavior anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-05-26 08:03 +0000
                Re: unexpected +LOOP behavior Mark Wills <markwills1970@gmail.com> - 2015-05-26 01:10 -0700
                Re: unexpected +LOOP behavior Michael Barry <barrym95838@yahoo.com> - 2015-05-26 22:31 -0700
                Re: unexpected +LOOP behavior Michael Barry <barrym95838@yahoo.com> - 2015-05-26 20:07 -0700
                Re: unexpected +LOOP behavior chitselb <chitselb@gmail.com> - 2015-05-26 20:20 -0700
                Re: unexpected +LOOP behavior Michael Barry <barrym95838@yahoo.com> - 2015-05-26 22:00 -0700
                Re: unexpected +LOOP behavior chitselb <chitselb@gmail.com> - 2015-05-27 02:41 -0700
  Re: unexpected +LOOP behavior anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-05-24 14:06 +0000

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