zlib/contrib/asm586

This is a patched version of zlib modified to use
Pentium-optimized assembly code in the deflation algorithm. The files
changed/added by this patch are:

README.586
match.S

The effectiveness of these modifications is a bit marginal, as the the
program's bottleneck seems to be mostly L1-cache contention, for which
there is no real way to work around without rewriting the basic
algorithm. The speedup on average is around 5-10% (which is generally
less than the amount of variance between subsequent executions).
However, when used at level 9 compression, the cache contention can
drop enough for the assembly version to achieve 10-20% speedup (and
sometimes more, depending on the amount of overall redundancy in the
files). Even here, though, cache contention can still be the limiting
factor, depending on the nature of the program using the zlib library.
This may also mean that better improvements will be seen on a Pentium
with MMX, which suffers much less from L1-cache contention, but I have
not yet verified this.

Note that this code has been tailored for the Pentium in particular,
and will not perform well on the Pentium Pro (due to the use of a
partial register in the inner loop).

If you are using an assembler other than GNU as, you will have to
translate match.S to use your assembler's syntax. (Have fun.)

Brian Raiter
breadbox@muppetlabs.com
April, 1998


Added for zlib 1.1.3:

The patches come from
http://www.muppetlabs.com/~breadbox/software/assembly.html

To compile zlib with this asm file, copy match.S to the zlib directory
then do:

CFLAGS="-O3 -DASMV" ./configure
make OBJA=match.o