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From: elg@killer.UUCP (Eric Green)
Newsgroups: comp.misc
Subject: Re: Assembly Language
Message-ID: <1371@killer.UUCP>
Date: Sat, 22-Aug-87 00:55:10 EDT
Article-I.D.: killer.1371
Posted: Sat Aug 22 00:55:10 1987
Date-Received: Sun, 23-Aug-87 12:57:54 EDT
References: <17981@amdcad.AMD.COM>
Organization: Bayou Telecommunications
Lines: 44

in article <17981@amdcad.AMD.COM>, tim@amdcad.AMD.COM (Tim Olson) says:
> 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.  

I must agree, with reservations. Note that my 5,000 lines of assembly language
assembles down to 7,000 bytes of 6502 machine code.  A "C" compiler for a
6502-based machine is a real porker... for example, a simple 1,000 line
text-formatter program (included with my "C" compiler) compiles down to about
25K of machine code.

However, when we are talking about real machines, with architectures designed
from the start to support high level languages (Chuck Peddle thought his
little chip would be used in electronic ovens, fer chrissakes, he had no idea
anybody could wrap a COMPUTER around it!), it's a different story.  For
example, I was unsatisfied with the performance of Jove on the Pyramids at
school. So I profiled it, and decided I would re-code the hot-spots into
assembly language. Well, to make a long process short, after printing out the
.s file and looking at a particular hot spot (the cursor positioning code),
there wasn't any darned way under the heavens for me to do much better than
the compiler had done... I figured a way of eliminating maybe 5 instructions
out of 50, and the resulting code didn't run appreciably faster (still
accounted for about the same percentage of CPU). Re-tooling the algorithm so
that the full cursor-positioning routine wasn't called for every darned
keystroke, would have saved jillions of microseconds more time than hitting
this particulr hot spot (alas, Jove is an example of a program that's nigh
unreadable... nowhere does he tell the PURPOSE of any particular variable,
file, or subroutine, leading to wild guesses as to what he's trying to do). 

Anyhow, after that, I looked at the output of several small utility programs
that I'd written, using various levels of the optimizer. Most of them, I
couldn't do a darn bit better by hand (I'm no expert in 90x assembler, but I
have written a couple thousand lines in it, so I'm no novice, either).
--
Eric Green   elg%usl.CSNET     Ollie North for President:
{cbosgd,ihnp4}!killer!elg      A man we can believe (in).
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