Subversion Repositories openrisc

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