From: Warner Losh <imp@bsdimp.com>
To: Noel Chiappa <jnc@mercury.lcs.mit.edu>
Cc: The Eunuchs Hysterical Society <tuhs@tuhs.org>
Subject: Re: [TUHS] Memory management in Dennis Ritchie's C Compiler
Date: Wed, 26 Aug 2020 10:09:06 -0600 [thread overview]
Message-ID: <CANCZdfrObnGUw+E1WAN-jdxqtyxEuCU_1K_zbtf7USnHfVLxow@mail.gmail.com> (raw)
In-Reply-To: <20200826155908.674C418C0CD@mercury.lcs.mit.edu>
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On Wed, Aug 26, 2020 at 9:59 AM Noel Chiappa <jnc@mercury.lcs.mit.edu>
wrote:
> > From: John Cowan
>
> > That's always true on the PDP-11 and Vax ... because the processor
> > architecture (which has pre-increment and post-decrement
> instructions,
> > but not their counterparts)
>
> After Doug's message, I carefull re-read this, and I'm not sure it's
> correct?
> The PDP-11 has pre-decrement and post-increment, not the other way around
> (as
> above) - unless I'm misunderstanding what you meant by those terms?
>
> That's why:
>
> *p++ = 0;
>
> turns (if p is in R2) into
>
> CLR (R2)+
>
> R2 is used, and then incremented after it has been used.
>
This quirk of the PDP-11 is why I still prefer post-increment and
pre-decrement in my code... even though there's no chance in hades that my
code will ever run there...
Warner
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next prev parent reply other threads:[~2020-08-26 16:09 UTC|newest]
Thread overview: 46+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-26 15:59 Noel Chiappa
2020-08-26 16:09 ` Warner Losh [this message]
2020-08-26 19:13 ` Clem Cole
2020-08-26 16:14 ` Jim Geist
2020-08-26 17:31 ` John Cowan
-- strict thread matches above, loose matches on Subject: below --
2020-08-27 8:37 Paul Ruizendaal
2020-08-26 13:24 Doug McIlroy
2020-08-26 15:41 ` John Cowan
2020-08-25 9:36 Steve Simon
2020-08-17 22:32 Norman Wilson
2020-08-17 22:55 ` Bakul Shah
2020-08-17 23:12 ` Chet Ramey
2020-08-18 6:33 ` arnold
2020-08-17 19:51 Noel Chiappa
2020-08-17 19:27 Noel Chiappa
2020-08-17 19:30 ` Larry McVoy
2020-08-17 19:44 ` Dan Halbert
2020-08-17 19:50 ` Paul Winalski
2020-08-17 22:05 ` Arthur Krewat
2020-08-18 0:52 ` Rob Gingell
2020-08-17 2:02 Noel Chiappa
2020-08-17 18:02 ` Paul Winalski
2020-08-17 18:13 ` Jim Geist
2020-08-17 18:48 ` Paul Winalski
2020-08-17 19:08 ` Jim Geist
2020-08-17 19:28 ` Paul Winalski
2020-08-17 19:35 ` Jim Geist
2020-08-17 19:41 ` Richard Salz
2020-08-17 23:40 ` Steffen Nurpmeso
2020-08-15 21:50 Dibyendu Majumdar
2020-08-16 15:20 ` arnold
2020-08-16 15:27 ` Jim Geist
2020-08-17 16:13 ` Dan Cross
2020-08-17 20:16 ` Dibyendu Majumdar
2020-08-17 20:34 ` Paul Winalski
2020-08-17 20:43 ` Dibyendu Majumdar
2020-08-17 21:05 ` Warner Losh
2020-08-17 22:47 ` Dave Horsfall
2020-08-17 23:06 ` Nemo Nusquam
2020-08-17 21:29 ` Dibyendu Majumdar
2020-08-24 15:58 ` Dan Cross
2020-08-24 17:08 ` John Cowan
2020-08-24 17:15 ` Clem Cole
2020-08-24 17:24 ` Clem Cole
2020-08-24 17:20 ` Dan Cross
2020-08-25 23:06 ` Arthur Krewat
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