Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!utgpu!water!watmath!clyde!cbosgd!ihnp4!inuxc!iuvax!pur-ee!j.cc.purdue.edu!k.cc.purdue.edu!l.cc.purdue.edu!cik
From: cik@l.cc.purdue.edu.UUCP
Newsgroups: comp.lang.c
Subject: Re: Types
Message-ID: <541@l.cc.purdue.edu>
Date: Wed, 10-Jun-87 14:24:40 EDT
Article-I.D.: l.541
Posted: Wed Jun 10 14:24:40 1987
Date-Received: Sat, 13-Jun-87 05:40:04 EDT
References: <7264@brl-adm.ARPA> <734@sdchema.sdchem.UUCP>, <293@osupyr.UUCP> <1173@ius2.cs.cmu.edu>
Organization: Purdue University Statistics Department
Lines: 106
Summary: Clarification of the problems

# In article <533@l.cc.purdue.edu>, cik@l.cc.purdue.edu (Herman Rubin) writes:
# > In article <8024@utzoo.UUCP>, henry@utzoo.UUCP (Henry Spencer) writes:
# > > But this sure doesn't sound like C, and C is what X3J11 is standardizing.
# > 
# > Okay, let me stick to nasty problems with C.
# > 
# > 	1.  Have the compiler substitute locations in -asm- statements.
# > 	Other than editing the assembler output, I do not believe there
# > 	is any way to insert asm statements which can be expected to
# > 	survive a change from one compiler to another.
# 
# 	I have no idea what you are talking about.  The asm statement
# 	allows you to insert assemble code into your C program, what
# 	is the problem you are having with this?

For example, suppose that the variable j has just been computed, and I want
to transfer on overflow to loc.  On the VAX, in C this is

	asm("	jov	xxx,LLL");

wher xxx is the location of j that the compiler has assigned and LLL is the
compiler's symbol for loc.  Sometimes, but not always, I can figure out where
the compiler has put j, but definitely not loc.  The only way I have been able
to do this is to put in something for xxx and LLL, get the assembler listing,
and then edit it.

# > 	2.  Require that the compiler honor, whenever possible, assignments
# > 	to registers.				      ^^^^^^^^
# 
# 	Is this really a problem?  Maybe I've been luckly, but when I ask
# 	for a register I get it provided I haven't used them all yet.

On the VAX, the compiler only lets me use half of the registers, and in cases
in which I wish to specify that a variable be in a specific register, it
refuses completely.  It refuses to put floating and double variables in
registers.  Also, using C compilers for both the VAX and the PYRAMID,
I have been unable to get the compiler to put a one-word union in a register.
# > 
# > 	3.  Allow the programmer to force non-promotion of floating to double,
# > 	whenever the programmer feels there is a good reason to do this.
# > 	I know when there is no point in using double; the compiler cannot.
# > 	Also, on some machines, one cannot print out a floating number in hex.
# > 	(Okay, I can finagle it.  But I had an occasion where this would have
# > 	been a problem.  I edited the assembler code, as the easiest option.)
# 
# 	But heres the problem - floatfunc(3.0),  should 3.0 be pass as
# 	a float or a double?  To complicate matters, say floatfunc is
# 	external. Function prototypes may take care of this though.
# 
# 	How about this to solve your problem.
# 
# 		typedef union 
# 			{
# 			float fnum;
# 			int inum;
# 			} floatint;
# 
I agree that your solution would work, and I would have used this method
if I had foreseen the problem.  However, if a variable is typed float, it
should be possible to pass it unpromoted in C without having to work.

# > 	4.  Allow floating point numbers to be given in hex.  Try putting in
# > 	2^-32 as a floating point or double constant.  Why should one have to
# > 	risk computer roundoff when it is totally unnecessary?
# 
# 	Some people have noted that this might be a niece feature, I forget
# 	what if any problems there are with this.
# 
There are no problems with this, but I do not know of any notation that has
been suggested to do this.
# > 
# > 	5.  Require that the compiler honor parentheses.  When I want a   
# > 	subroutine to return (x - y - k*c) + f(y), I most emphatically do
# > 	not want the compiler to do the "obvious" rearrangement to combine
# > 	the two terms with y; this can be a major loss of accuracy.  To set
# > 	a variable equal to the parenthetical expression is a significant
# > 	loss of time.
# 
# 	What two terms with y?  I hope my C compiler doesn't think y can
# 	be factor out of that expression to form (f-1)(y) :-).

The two terms are -y and f(y).

# 	To address your real complaint, the ANSI standard plans on supporting
# 	parenthesis honoring through the use of the unary +. +(x - y) + y
# 	will be evaluated as it appears.
# 
I have no objection to the unary +, but many of the commentators in this
news group seem to.

# 	Please lets not get into a long philosophic debate over this
# 	we have seen it all before.  If you don't like it, use another
# 	language.

If there were another appropriate language, I would.  None of the other
languages I know (except PL/1, which is unnecessarily clumsy) do any better.

# 					Eddie Wyatt
# 
# e-mail: edw@ius2.cs.cmu.edu


-- 
Herman Rubin, Dept. of Statistics, Purdue Univ., West Lafayette IN47907
Phone: (317)494-6054
hrubin@l.cc.purdue.edu or pur-ee!stat-l!cik or hrubin@purccvm.bitnet