[TUHS] Fwd: [Simh] An abandoned piece of K&R C

[Steve Johnson]

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

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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

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