The Unix Heritage Society mailing list
 help / color / mirror / Atom feed
From: scj@yaccman.com (Steve Johnson)
Subject: [TUHS] Fwd: [Simh] An abandoned piece of K&R C
Date: Sun, 05 Nov 2017 08:18:33 -0800	[thread overview]
Message-ID: <2b6fb33181aef8a68f6a6a21ff08a82271389a6a@webmail.yaccman.com> (raw)
In-Reply-To: <160331EE-3C7D-4948-ADE3-E57FFDCA5EAF@serissa.com>

[-- Warning: decoded text below may be mangled, UTF-8 assumed --]
[-- Attachment #1: Type: text/plain, Size: 2600 bytes --]

I'm not aware of any C implementation that actually generated code for
MAX and MIN using these operators, although the operators were
certainly discussed with that spelling.  I think many people just
made do with:   #define MAX(a,b)  ((a)>(b))?(a):(b)
despite the fact that it is wrong if a or b has side effects.   And
with register variables, you could generate excellent code for max and
min if that was a consideration.

I think the reason was partly that the operators look a bit clunky. 
 And also that the implementation, like ? :, can be trickier than it
first appears...

Steve

----- Original Message -----
From:
 "Lawrence Stewart" <stewart at serissa.com>

To:
"The Eunuchs Hysterical Society" <tuhs at tuhs.org>
Cc:

Sent:
Fri, 3 Nov 2017 08:53:40 -0400
Subject:
[TUHS] Fwd: [Simh] An abandoned piece of K&R C

 This caught my attention.  Did early C really have min and max?
 Were they used for anything?  In those days I was a BCPL user,
which IIRC, did not have such things.

-Larry

Begin forwarded message:

FROM: 
Leo Broukhis <leob at mailcom.com [1]>

SUBJECT: 
[SIMH] AN ABANDONED PIECE OF K&R C

DATE: 
2017, November 3 at 1:14:42 AM EDT

TO: 
"simh at trailing-edge.com [2]" <simh at trailing-edge.com [3]>

https://retrocomputing.stackexchange.com/q/4965/4025 [4]

In the UNIX V7 version of the C language, there were the / (min) and
the / (max) operators. In the source of the scanner part of the
compiler,

case BSLASH:
    if (subseq('/', 0, 1))
        return(MAX);
    goto unkn;

case DIVIDE:
    if (subseq('', 0, 1))
        return(MIN);
...

However, attempting to use them reveals that the corresponding part in
the code generator is missing. Trying to compile

foo(a, b) { return a / b; }

results in

1: No code table for op: /

The scanner piece survived in the copies of the compiler for various
systems for several years. I tried to look for copies of the code
generator table which would contain an implementation, but failed. Has
anyone ever seen a working MIN/MAX operator in K&R C?

Thanks,Leo

 _______________________________________________
Simh mailing list
Simh at trailing-edge.com [5]
http://mailman.trailing-edge.com/mailman/listinfo/simh



Links:
------
[1] mailto:leob at mailcom.com
[2] mailto:simh at trailing-edge.com
[3] mailto:simh at trailing-edge.com
[4] https://retrocomputing.stackexchange.com/q/4965/4025
[5] mailto:Simh at trailing-edge.com

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://minnie.tuhs.org/pipermail/tuhs/attachments/20171105/6976251a/attachment.html>


      reply	other threads:[~2017-11-05 16:18 UTC|newest]

Thread overview: 2+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <CAFmvRsc46TQ10nEHewBt=LpQ814GydW-BmQ+=-jyvitMP1numg@mail.gmail.com>
2017-11-03 12:53 ` Lawrence Stewart
2017-11-05 16:18   ` Steve Johnson [this message]

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=2b6fb33181aef8a68f6a6a21ff08a82271389a6a@webmail.yaccman.com \
    --to=scj@yaccman.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).