Path: utzoo!attcan!uunet!lll-winken!lll-tis!mordor!joyce!ames!ucsd!rutgers!njin!princeton!phoenix!pucc!EGNILGES
From: EGNILGES@pucc.Princeton.EDU (Ed Nilges)
Newsgroups: comp.lang.fortran
Subject: Re: Fortran vs C for computations
Message-ID: <6065@pucc.Princeton.EDU>
Date: 12 Sep 88 18:22:58 GMT
References: <962@amelia.nas.nasa.gov> <3290@lanl.gov> <3169@emory.uucp> <1225@scolex>
Reply-To: EGNILGES@pucc.Princeton.EDU
Organization: Princeton University, NJ
Lines: 53
Disclaimer: Author bears full responsibility for contents of this article

In article <1225@scolex>, seanf@sco.COM (Sean Fagan) writes:
 
>In article <3169@emory.uucp> platt@emory.UUCP (Dan Platt) writes:
>>>#ifdef is an admission that your compiler isn't any good.  If the
>>>conditional expression is a constant, a normal if statement should
>>>be optimized so that code is only generated for the active branch.  If
>>>the conditional expression is not a constant, it couldn't be used as
>>>part of an #ifdef either.
>[sorry, don't have the original author's name.  Somebody from Los Alamos, I
>think]
>
>This is *wrong*.
 
 
It sure the hell is.  In reference (1), Brian Kernighan says, code what
you mean.  Macro facilities (even the still-primitive-after-all-these-
years facilities of C) allow the software engineer (as opposed to the
hacker) to declare an intent to control how the software shall exist
in various environments.  #ifdef & the macro processor in general allows
the C programmer to define a range of potential compilation and execution
environments.  For example, if I am writing a program to run both on
ASCII machines and the IBM 370, which is an EBCDIC machine, the following
should be source compatible (altho I have not tested it, and it assumes
that either ASCII or EBCDIC will be defined)
 
 
     #ifdef EBCDIC
          /* Boo */
          isalpha = ( inchar>='a' && inchar<='i'
                      ||
                      inchar>='j' && inchar<='r'
                      ||
                      inchar>='s' && inchar<='z'
                      ||
                      inchar>='A' && inchar<='I'
                      ||
                      inchar>='J' && inchar<='R'
                      ||
                      inchar>='S' && inchar<='Z' );
     #endif
     #ifdef ASCII
          /* Yay */
          isalpha = ( inchar>='a' && inchar<='z'
                      ||
                      inchar>='A' && inchar<='Z' )
     #endif
 
 
Indeed, the whole technique of conditional assembly, used heavily within
IBM to generate systems across a variety of environments, is so little
used in HLLs that a name for it does not roll easily off the tongue.  This
will be the case until CS departments realize that wisecracks about
machines you don't like won't get you off the hook when you have to port
your code.  When will C have a decent conditional compiler?