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From: Leisner.Henr@xerox.com (marty)
Newsgroups: comp.lang.c
Subject: Re: Available No. of Registers
Message-ID: <2855@brl-adm.ARPA>
Date: Tue, 20-Jan-87 19:13:10 EST
Article-I.D.: brl-adm.2855
Posted: Tue Jan 20 19:13:10 1987
Date-Received: Wed, 21-Jan-87 03:13:30 EST
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Some more insights on coding style using register variables for
effiency.

I've done a lot of real-time coding with Manx Aztec C for 8085 machines.
Manx allows one register variable (stored in the BC pair).

When the code can be non-reentrant, I've found it effective to pick one
good variable (often a pointer to structure) to be register and the rest
static.  Stack operations are expensive on 8080 architectures and
real-time performance is important.

Any additional register declarations beyond the first Manx treats as
auto (which means stack, which is undesirable).  There is a compile time
option to convert autos to statics.  

I've usually been pretty happy with the assembly language this compiler
generates.  I feel if at all possible it is better to stay away from
assembly language for any meaningful algorithms.  Significant
optimization can be performed on small machines by "fiddling" with the C
source and understanding the compiler output.  Of course, oddball
implementations with the idea the intent of increased speed should
thoroughly commented.

marty
leisner.henr@xerox.com