Xref: utzoo comp.lang.c:8768 comp.sys.ibm.pc:13952
Path: utzoo!utgpu!water!watmath!clyde!rutgers!tut.cis.ohio-state.edu!husc6!cca!mirror!premise!chang
From: chang@premise.ZONE1.COM (John Chang)
Newsgroups: comp.lang.c,comp.sys.ibm.pc
Subject: Re: cdecl keyword
Summary: Why cdecl is a keyword
Keywords: cdecl MicroSoft C keywords
Message-ID: <185@premise.ZONE1.COM>
Date: 2 Apr 88 09:18:23 GMT
References: <1238@wjvax.UUCP> <297@ho7cad.ATT.COM> <1242@wjvax.UUCP> <3867@super.upenn.edu>
Organization: Premise, Inc., Cambridge, MA
Lines: 59

Roberto Shironoshita writes:
> Rahul Dhesi writes:
> >[ cc -pascal mystuff.c ]
> >If mystuff.c uses any C library function, you still want that library
> >function to be called using the C calling convention, even though you
> >asked the compiler to generate code for the Pascal calling convention.
>
> I would much rather do away with the switch to generate foreign
> calling conventions, and assume anything is a C function unless
> otherwise declared.
> >With a little foresight Microsoft could have just used the same calling
> >convention in all its language translators.
> 
> I am of the belief that most languages have their own calling
> conventions: FORTRAN uses pass-by-reference for everything (at least,
> that's what I heard last); PASCAL uses pass-by-value for regular
> parameters, and pass-by-reference for VAR parameters.  C uses
> pass-by-value for everything.
		    ^^^^^^^^^^ What about arrays? 

The calling convention we're talking about here isn't call-by-name or
call-by-value.  It's simply the order in which parameters are passed
on the stack.  And in C, that order *must* be right to left in order
to support variable length functions like printf.  If it were left to
right, then the printf function wouldn't know where to find its format
string.

However, the right to left parameter passing takes more code space
(one extra instruction to fix the stack after a function call) and
hence takes longer to execute than 'pascal' calling convention 
(left-to-right parameter passing).

That's the reason the cdecl and pascal keywords exist.  Although
Microsoft could have made all their languages use the same parameter
passing convention, this would have meant generating less efficient code.

The extra instruction needed to pop the stack after a function call
seems unimportant, yet I once heard Microsoft claim that the change to
pascal calling convention made Microsoft Windows "substantially"
smaller and faster.  I don't remember the figures, but they were
hard to believe.

If you're writing functions with a variable number of parameters, and
want to take advantage of the more efficient pascal calling convention,
you still have to worry about the portability of these keywords.  One solution
is to #define environment-dependent tokens for the keywords.

How about the far and huge keywords?  Parsing declarations was bad enough
without these.  Quick, what's the difference between far int (*f)() and
int far (*f)()?  But this is more a gripe about the Intel architecture than
anything else.

John Chang		{ ...harvard!eddie,...cbosgd!mirror}!premise!chang
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