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From: tim@amdcad.AMD.COM (Tim Olson)
Newsgroups: comp.misc
Subject: Re: Assembly Language
Message-ID: <17981@amdcad.AMD.COM>
Date: Thu, 20-Aug-87 18:39:22 EDT
Article-I.D.: amdcad.17981
Posted: Thu Aug 20 18:39:22 1987
Date-Received: Sat, 22-Aug-87 12:13:44 EDT
References: <892@edge.UUCP> <1305@faline.bellcore.com>
Reply-To: tim@amdcad.UUCP (Tim Olson)
Organization: Advanced Micro Devices, Inc., Sunnyvale, Ca.
Lines: 45

In article <1305@faline.bellcore.com> gtchen@faline.UUCP (George T. Chen) writes:
+-----
|But I'm sure the actual piece of executable code in orders of magnitude
|smaller than the equivalent C program.  Also, I've assumed that since you
|did the program in assembly, then it will probably run faster.  For that
|matter, any program done in any HLL can be done in assembly and made to
|run as fast if not faster.
+-----

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.

	-- Tim Olson
	Advanced Micro Devices
	(tim@amdcad.amd.com)