Re: Portability

From	Andrew Haley <andrew29@littlepinkcloud.invalid>
Subject	Re: Portability
Newsgroups	comp.lang.forth
References	(7 earlier) <kkmkt2$gtt$1@dont-email.me> <sYadnc_kj7UfivLMnZ2dnUVZ_qudnZ2d@supernews.com> <kkpmse$mm9$1@dont-email.me> <_ZadnYKzjIf69u3MnZ2dnUVZ_s6dnZ2d@supernews.com> <2013Apr22.115903@mips.complang.tuwien.ac.at>
Message-ID	<3rGdnTef2dZksejMnZ2dnUVZ_i2dnZ2d@supernews.com> (permalink)
Date	2013-04-22 07:28 -0500

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Anton Ertl <anton@mips.complang.tuwien.ac.at> wrote:
> Andrew Haley <andrew29@littlepinkcloud.invalid> writes:
>>rickman <gnuarm@gmail.com> wrote:
>>> On 4/17/2013 5:43 PM, Andrew Haley wrote:
>>>> You don't need special overflow detection, or extra comparisons: it's
>>>> a lot easier to flip the sign bits of both operands and then do a U<  .
> 
> Which requires the same effort to implement based on 0< as <.

I don't understand this remark.  What does "based on 0< as <" mean?

>>Yes.  You really do need a carry flag in a processor, I would have
>>thought.
> 
> MIPS and Alpha show that you don't.

Not really.  Well, alright, I suppose it's possible to get away with
having to calculate the carry yourself, in an
everything-is-possible-on-a-Turing-machine way, but it's unpleasant.

> They provide instructions for < and U<, however; and they compute
> sum-with-carry as follows:
> 
> : +c ( u1 u2 -- u uc )
> \ uc is the carry of u1+u2
> over + dup rot u< ;

In which case they *do* have a carry flag, it's just that you have to
do a separate U< to get it; for what is U< but the carry out of a
subtraction?  In the context of a Forth CPU, Novix's +c is a much
better idea.

Andrew.

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 Portability kenney@cix.compulink.co.uk - 2013-04-06 04:12 -0500
  Re: Portability albert@spenarnc.xs4all.nl (Albert van der Horst) - 2013-04-06 11:31 +0000
    Re: Portability "Elizabeth D. Rather" <erather@forth.com> - 2013-04-06 10:34 -1000
      Re: Portability "Ed" <invalid@nospam.com> - 2013-04-09 09:56 +1000
        Re: Portability albert@spenarnc.xs4all.nl (Albert van der Horst) - 2013-04-09 01:30 +0000
          Re: Portability anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-04-09 07:21 +0000
            Re: Portability "Elizabeth D. Rather" <erather@forth.com> - 2013-04-08 22:18 -1000
              Re: Portability anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-04-09 12:41 +0000
                Re: Portability Coos Haak <chforth@hccnet.nl> - 2013-04-09 17:21 +0200
                Re: Portability "Elizabeth D. Rather" <erather@forth.com> - 2013-04-09 08:06 -1000
                Re: Portability Bernd Paysan <bernd.paysan@gmx.de> - 2013-04-09 22:34 +0200
                Re: Portability "Elizabeth D. Rather" <erather@forth.com> - 2013-04-09 12:05 -1000
                Re: Portability "Elizabeth D. Rather" <erather@forth.com> - 2013-04-09 14:19 -1000
                Re: Portability Chris <xrissmith@me.com> - 2013-04-09 20:45 -0700
                Re: Portability "Ed" <invalid@nospam.com> - 2013-04-10 14:02 +1000
                Re: Portability Hugh Aguilar <hughaguilar96@yahoo.com> - 2013-04-09 23:00 -0700
                Re: Portability "WJ" <w_a_x_man@yahoo.com> - 2013-04-12 14:41 +0000
                Re: Portability "Ed" <invalid@nospam.com> - 2013-04-13 15:34 +1000
                Re: Portability anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-04-10 15:19 +0000
                Re: Portability albert@spenarnc.xs4all.nl (Albert van der Horst) - 2013-04-10 11:46 +0000
                Re: Portability anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-04-10 15:03 +0000
                Re: Portability Hugh Aguilar <hughaguilar96@yahoo.com> - 2013-04-09 18:28 -0700
            Re: Portability Hugh Aguilar <hughaguilar96@yahoo.com> - 2013-04-09 17:00 -0700
          Re: Portability "Ed" <invalid@nospam.com> - 2013-04-10 13:00 +1000
            Re: Portability albert@spenarnc.xs4all.nl (Albert van der Horst) - 2013-04-10 11:55 +0000
              Re: Portability Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-04-10 10:10 -0500
                Re: Portability anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-04-10 15:56 +0000
                Re: Portability Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-04-10 16:18 -0500
                Re: Portability anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-04-11 13:24 +0000
                Re: Portability Hugh Aguilar <hughaguilar96@yahoo.com> - 2013-04-11 20:50 -0700
                Re: Portability Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-04-12 04:17 -0500
                Re: Portability anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-04-12 13:43 +0000
                Re: Portability Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-04-12 11:08 -0500
                Re: Portability albert@spenarnc.xs4all.nl (Albert van der Horst) - 2013-04-12 18:50 +0000
                Re: Portability Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-04-13 03:57 -0500
                Re: Portability anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-04-13 11:59 +0000
                Re: Portability Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-04-13 14:47 -0500
                Re: Portability rickman <gnuarm@gmail.com> - 2013-04-12 10:44 -0400
                Re: Portability Bernd Paysan <bernd.paysan@gmx.de> - 2013-04-15 16:20 +0200
                Re: Portability "Elizabeth D. Rather" <erather@forth.com> - 2013-04-16 08:12 -1000
                Re: Portability "A.K." <akk@nospam.org> - 2013-04-16 22:21 +0200
                Re: Portability Bernd Paysan <bernd.paysan@gmx.de> - 2013-04-16 22:33 +0200
                Re: Portability "Ed" <invalid@nospam.com> - 2013-04-19 15:04 +1000
                Re: Portability anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-04-15 15:46 +0000
                Re: Portability Sieur de Bienville <morrimichael@gmail.com> - 2013-04-15 19:19 -0700
                Re: Portability anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-04-16 12:53 +0000
                Re: Portability rickman <gnuarm@gmail.com> - 2013-04-16 17:29 -0400
                Re: Portability "Elizabeth D. Rather" <erather@forth.com> - 2013-04-16 11:44 -1000
                Re: Portability rickman <gnuarm@gmail.com> - 2013-04-16 18:00 -0400
                Re: Portability Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-04-16 17:33 -0500
                Re: Portability "Elizabeth D. Rather" <erather@forth.com> - 2013-04-16 12:46 -1000
                Re: Portability rickman <gnuarm@gmail.com> - 2013-04-17 13:09 -0400
                Re: Portability Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-04-17 12:20 -0500
                Re: Portability "Elizabeth D. Rather" <erather@forth.com> - 2013-04-17 07:38 -1000
                Re: Portability Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-04-17 16:43 -0500
                Re: Portability rickman <gnuarm@gmail.com> - 2013-04-17 20:03 -0400
                Re: Portability Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-04-18 16:53 -0500
                Re: Portability rickman <gnuarm@gmail.com> - 2013-04-18 18:02 -0400
                Re: Portability Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-04-19 03:30 -0500
                Re: Portability rickman <gnuarm@gmail.com> - 2013-04-19 15:31 -0400
                Re: Portability anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-04-22 09:59 +0000
                Re: Portability Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-04-22 07:28 -0500
                Re: Portability anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-04-22 15:27 +0000
                Re: Portability Hugh Aguilar <hughaguilar96@yahoo.com> - 2013-04-22 18:16 -0700
                Re: Portability anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-04-17 10:23 +0000
                Re: Portability rickman <gnuarm@gmail.com> - 2013-04-17 13:46 -0400
                Re: Portability anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-04-22 09:47 +0000
                Re: Portability Brad Eckert <hwfwguy@gmail.com> - 2013-04-17 10:32 -0700
                Re: Portability nobody@nowhere - 2013-04-17 17:36 +0000
                Re: Portability rickman <gnuarm@gmail.com> - 2013-04-17 14:21 -0400
                Re: Portability Brad Eckert <hwfwguy@gmail.com> - 2013-04-17 15:03 -0700
                Re: Portability rickman <gnuarm@gmail.com> - 2013-04-17 18:22 -0400
                Re: Portability rickman <gnuarm@gmail.com> - 2013-04-17 18:24 -0400
                Re: Portability rickman <gnuarm@gmail.com> - 2013-04-18 00:51 -0400
                Re: Portability rickman <gnuarm@gmail.com> - 2013-04-18 17:19 -0400
                Re: Portability Brad Eckert <hwfwguy@gmail.com> - 2013-04-19 12:37 -0700
                Re: Portability rickman <gnuarm@gmail.com> - 2013-04-19 15:53 -0400
                Re: Portability Lars Brinkhoff <lars.spam@nocrew.org> - 2013-04-17 19:26 +0200
                Re: Portability albert@spenarnc.xs4all.nl (Albert van der Horst) - 2013-04-10 18:50 +0000
                Re: Portability Bernd Paysan <bernd.paysan@gmx.de> - 2013-04-10 22:14 +0200
                Re: Portability Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-04-12 04:18 -0500
                Re: Portability "Elizabeth D. Rather" <erather@forth.com> - 2013-04-12 08:30 -1000
                Re: Portability albert@spenarnc.xs4all.nl (Albert van der Horst) - 2013-04-12 18:58 +0000
                Re: Portability "Elizabeth D. Rather" <erather@forth.com> - 2013-04-12 11:29 -1000
              Re: Portability "Ed" <invalid@nospam.com> - 2013-04-13 14:57 +1000
        Re: Portability Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-04-09 04:11 -0500

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