5 Nov
2017
5 Nov
'17
5:18 p.m.
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(a)serissa.com>
To:
"The Eunuchs Hysterical Society" <tuhs(a)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(a)mailcom.com [1]>
SUBJECT:
[SIMH] AN ABANDONED PIECE OF K&R C
DATE:
2017, November 3 at 1:14:42 AM EDT
TO:
"simh(a)trailing-edge.com [2]" <simh(a)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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