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Re: Challenge for Christmas

From anton@mips.complang.tuwien.ac.at (Anton Ertl)
Newsgroups comp.lang.forth
Subject Re: Challenge for Christmas
Date 2016-12-26 14:58 +0000
Organization Institut fuer Computersprachen, Technische Universitaet Wien
Message-ID <2016Dec26.155852@mips.complang.tuwien.ac.at> (permalink)
References (1 earlier) <2016Dec25.175253@mips.complang.tuwien.ac.at> <c87c7c04-7c90-4d38-84d2-996c42c27f1f@googlegroups.com> <o3p28k$65t$1@dont-email.me> <2016Dec26.142126@mips.complang.tuwien.ac.at> <2016Dec26.145757@mips.complang.tuwien.ac.at>

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anton@mips.complang.tuwien.ac.at (Anton Ertl) writes:
>Again, we see that the existing counted-loop words (including Gforth's
>U-DO ... -LOOP) are not a good fit striding backwards through an
>array.  One would have to do the decrement first, and leave the loop
>when crossing the boundary between limit and limit-1.  Maybe with a
>syntax like
>
>U-DO
>  ( u ) DECREMENT
>  ...
>REPEAT
>
>The code above would become:
>
>: product? ( n addr u -- )
>    \ is n a product of the numbers in addr u?
>    cells over + u-do
>       cell decrement
>	  begin
>	    dup i @ /mod swap 0= while ( n1 n2 )
>		nip repeat
>          drop repeat
>    1 = ;
>    
>The setup in front of the U-DO becomes quite a bit simpler.

Given that the convention for specifying arrays is "addr count", why
not simplify the setup even further and have

addr count stride A+DO ... A+LOOP \ i goes from addr...addr+(count-1)*stride
addr count stride A-DO ... A-LOOP \ i goes from addr+(count-1)*stride...addr

The example would become:

: product? ( n addr u -- )
    \ is n a product of the numbers in addr u?
    cell a-do ( n1 )
	  begin
	    dup i @ /mod swap 0= while ( n1 n2 )
		nip repeat
          drop a-loop
    1 = ;

- 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 2016: http://www.euroforth.org/ef16/

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Challenge for Christmas lehs <skydda.barnen@gmail.com> - 2016-12-24 06:10 -0800
  Re: Challenge for Christmas november.nihal@gmail.com - 2016-12-24 14:17 -0800
    Re: Challenge for Christmas mhx@iae.nl - 2016-12-24 15:37 -0800
    Re: Challenge for Christmas mhx@iae.nl - 2016-12-24 15:43 -0800
    Re: Challenge for Christmas lehs <skydda.barnen@gmail.com> - 2016-12-25 01:25 -0800
      Re: Challenge for Christmas november.nihal@gmail.com - 2016-12-25 06:59 -0800
        Re: Challenge for Christmas lehs <skydda.barnen@gmail.com> - 2016-12-25 07:26 -0800
          Re: Challenge for Christmas november.nihal@gmail.com - 2016-12-25 07:57 -0800
            Re: Challenge for Christmas lehs <skydda.barnen@gmail.com> - 2016-12-25 08:07 -0800
              Re: Challenge for Christmas november.nihal@gmail.com - 2016-12-25 08:25 -0800
  Challenge for Christmas Ilya Tarasov <ilya74.tarasov@gmail.com> - 2016-12-25 07:39 -0800
  Re: Challenge for Christmas anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2016-12-25 16:52 +0000
    Re: Challenge for Christmas lehs <skydda.barnen@gmail.com> - 2016-12-25 09:33 -0800
      Re: Challenge for Christmas Gerry Jackson <gerry@jackson9000.fsnet.co.uk> - 2016-12-25 18:15 +0000
        Re: Challenge for Christmas lehs <skydda.barnen@gmail.com> - 2016-12-25 13:21 -0800
          Re: Challenge for Christmas november.nihal@gmail.com - 2016-12-25 16:51 -0800
            Re: Challenge for Christmas lehs <skydda.barnen@gmail.com> - 2016-12-26 00:48 -0800
              Re: Challenge for Christmas lehs <skydda.barnen@gmail.com> - 2016-12-26 01:36 -0800
              Re: Challenge for Christmas lehs <skydda.barnen@gmail.com> - 2016-12-26 01:39 -0800
                Re: Challenge for Christmas november.nihal@gmail.com - 2016-12-26 04:36 -0800
                Re: Challenge for Christmas lehs <skydda.barnen@gmail.com> - 2016-12-26 07:40 -0800
                Re: Challenge for Christmas anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2016-12-26 15:53 +0000
                Re: Challenge for Christmas lehs <skydda.barnen@gmail.com> - 2016-12-26 08:57 -0800
                Re: Challenge for Christmas anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2016-12-27 13:12 +0000
                Re: Challenge for Christmas albert@cherry.spenarnc.xs4all.nl (Albert van der Horst) - 2016-12-27 16:58 +0100
                Re: Challenge for Christmas anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2016-12-27 16:01 +0000
                Re: Challenge for Christmas albert@cherry.spenarnc.xs4all.nl (Albert van der Horst) - 2016-12-27 19:10 +0100
                Re: Challenge for Christmas anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2016-12-27 18:08 +0000
                Re: Challenge for Christmas albert@cherry.spenarnc.xs4all.nl (Albert van der Horst) - 2016-12-27 20:13 +0100
                Re: Challenge for Christmas anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2016-12-28 08:19 +0000
                Re: Challenge for Christmas albert@cherry.spenarnc.xs4all.nl (Albert van der Horst) - 2016-12-28 12:49 +0100
                Re: Challenge for Christmas anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2016-12-28 14:26 +0000
                Re: Challenge for Christmas anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2016-12-29 13:13 +0000
                Re: Challenge for Christmas lehs <skydda.barnen@gmail.com> - 2016-12-27 12:29 -0800
                Re: Challenge for Christmas albert@cherry.spenarnc.xs4all.nl (Albert van der Horst) - 2016-12-27 22:25 +0100
                Re: Challenge for Christmas lehs <skydda.barnen@gmail.com> - 2016-12-27 14:19 -0800
                Re: Challenge for Christmas november.nihal@gmail.com - 2016-12-27 14:14 -0800
                Re: Challenge for Christmas anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2016-12-28 11:06 +0000
                Re: Challenge for Christmas lehs <skydda.barnen@gmail.com> - 2016-12-28 04:22 -0800
              Re: Challenge for Christmas john <anon@example.com> - 2016-12-26 13:05 +0000
                Re: Challenge for Christmas lehs <skydda.barnen@gmail.com> - 2016-12-26 07:45 -0800
          Re: Challenge for Christmas Gerry Jackson <gerry@jackson9000.fsnet.co.uk> - 2016-12-26 07:44 +0000
        Re: Challenge for Christmas anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2016-12-26 13:21 +0000
          Re: Challenge for Christmas anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2016-12-26 13:57 +0000
            Re: Challenge for Christmas anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2016-12-26 14:58 +0000
  Re: Challenge for Christmas albert@cherry.spenarnc.xs4all.nl (Albert van der Horst) - 2016-12-26 17:24 +0100
    Re: Challenge for Christmas lehs <skydda.barnen@gmail.com> - 2016-12-26 09:15 -0800
    Re: Challenge for Christmas lehs <skydda.barnen@gmail.com> - 2016-12-26 11:45 -0800
    Re: Challenge for Christmas lehs <skydda.barnen@gmail.com> - 2016-12-30 10:47 -0800
      Re: Challenge for Christmas albert@cherry.spenarnc.xs4all.nl (Albert van der Horst) - 2016-12-31 15:31 +0100
        Re: Challenge for Christmas lehs <skydda.barnen@gmail.com> - 2016-12-31 10:53 -0800

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