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From: pf@diab.UUCP (Per Fogelstrom)
Newsgroups: comp.misc
Subject: Re: Assembly Language
Message-ID: <300@diab.UUCP>
Date: Mon, 24-Aug-87 05:24:03 EDT
Article-I.D.: diab.300
Posted: Mon Aug 24 05:24:03 1987
Date-Received: Thu, 27-Aug-87 07:18:24 EDT
References: <892@edge.UUCP> <1305@faline.bellcore.com> <17981@amdcad.AMD.COM>
Reply-To: pf@.UUCP (Per Fogelstrom)
Organization: Diab Data AB, Taby, Sweden
Lines: 98
Summary: After 17 years, i vote for HLL.

In article <17981@amdcad.AMD.COM> tim@amdcad.UUCP (Tim Olson) writes:
>
>Only if the person writing the assembly language is very good.  The new
>highly-optimizing C compilers are becoming *very* good at what they do. 
>For example, one compiler I am familiar with compiled the code fragment:
>
>	if (x[i] > x[i+1]) {
>		temp = x[i];
>		x[i] = x[i+1];
>		x[i+1] = temp;
>	}
>
>to:
>	const	base, _x		; calculate address of x[i]
>	consth	base, _x
>	sll	temp, i, 2
>	add	base, base, temp
>	load	val1, base		; get value of x[i]
>	add	base2, base, 4		; calculate address of x[i+1]
>	load	val2, base		; get value of x[i+1]
>
>	cpgt	temp, val1, val2	; perform "if"
>	jmpf	temp, $endif
>	nop
>
>	store	val1, base2		; swap operands
>	store	val2, base
>
>
>
>Note that the compiler optimized the array calculation expressions to
>reuse a common sub-expression (x[i]), and that it totally optimized away
>the temp variable used to swap the values!  I don't think you could
>write it in assembly language any better than that.

Oh dear! This really confirms what i allways suspected about risc cpu's.
Very happy that i've givi'n up ass'(mbly) programming :-))))).

This example should really scare away the "assembly programmers"! TWELVE !!
instructions for doing something that should not take more than FIVE !!
And keeping track of the register contents even if they have mnemonic names!
I have tested the example on our own C-compiler genereating code for the
famous (:-)) NS32000 cpu, and it throws this out:

	cmpd	4(r1)[r0:d],r1[r0:d]
	bge	donotdothis
	movd	r1[r0:d],r2
	movd	4(r1)[r0:d],r1[r0:d]
	movd	r2,4(r1)[r0:d]

Before You start to flaming me about performence; I just wanted to show the
difference between a risc and a cisc's solution to the same HLL code. I think
my example is easier to read, but it does not justify that it should be
written in assembler rather than C.

A bad compiler should not justify writing a program in assembly. Even if
the generated code size sticks in your eyes. The extra time spent on
writing the same program in assembly is a waste, unless there are aspects
of performence put into it. Compilers improve (mostly) and if you are
lucky, you might be able to recompile the program with a better compiler later.
(I've been using the first 'PLM' compiler for the i8008 and i8080. It was
a terrible thing. It was trying to drown the programmer in machine code.
BUT! it improved, generating better code, and fewer bugs !).

I have seventeen(17) years of experience in assembly programming. (My first
on an IBM 1401, if that can be called assembly :-)). I have worked with the
development of three real time operating systems, the last one a UN*X SV
compatible and in "C". I've spent a whole summer squezing 6 kbytes out of
a 20 kbytes basic interpreter for a PC (and that before the IBM era).. Guess
how that code looked after that :-).So i think i have a pretty good idea
about the difference between assembly and HLL.

So let the suicide-makers program in assembly, even if they don't have to.
I don't bother unless i have to maintain any of their code.

Conclusion: One should have *very* good reasons (read "very high speed
	    requirements") for using assembly. People defending assembly
	    for large programming projects does'nt belive in porting.
	    The just belive that there is only one kind of cpu type
	    on the market. Programmers should spend more time on writing
	    comments explaining what the program does and how, than
	    writing "clever" assembly code that no one exept an "expert"
	    can understand. Using the same time effort for writing the
	    same program in assembly and in some HL- language "should"
	    produce a better documented program in HLL.

	AND REMEMBER !!!!!!!  NO PROGRAM LANGUAGE IS SELF-DOCUMENTING !!!!
	How understandable and maintinable a program is, depends *ONLY* on
	how good the documentation is. Nonsens comments like "moving this
	data here and that data there" is not documentation, it's filling.
	Explain *WHY* i'ts moved etc.!

   ** ASK ME !   I WILL SHURLEY VOTE FOR HLL  **
-- 
Per Fogelstrom,  Diab Data AB
SNAIL: Box 2029, S-183 02 Taby, Sweden
ANALOG: +46 8-7680660
UUCP: seismo!mcvax!enea!diab!pf