etherboot-developers

[Etherboot-developers] upx compressor/decompressor...

[Eric W B. <ebi...@ln...>]

Yeah!  I have just incoporated the nrv2b algorthim from
upx into etherboot.  And I have built an image with
all of the etherboot drivers.

-rwxrwxr-x    1 eric     eric       136080 Aug 21 02:52 bin32/etherboot.img*
-rwxrwxr-x    1 eric     eric        64912 Aug 21 02:52 bin32/etherboot.nrv2bimg
$ size bin32/unnrv2b.o      
   text    data     bss     dec     hex filename
    180       0       0     180      b4 bin32/unnrv2b.o

In it's final form the overhead for the nrv2b decompressor is just
180 bytes and should handle any size of file.  The 32bit infrastructure
is now an advantage instead of a liability size wise.

I will be adding targets etherboot, etherboot-pci, and etherboot-isa
shortly and then checking this code in.

Eric

Re: [Etherboot-developers] upx compressor/decompressor...

[Markus G. <ma...@gu...>]

Eric W Biederman wrote:
> In it's final form the overhead for the nrv2b decompressor is just
> 180 bytes and should handle any size of file.  The 32bit infrastructure
> is now an advantage instead of a liability size wise.

Sweet! That's very impressive. Now, if only there was some documentation on 
these algorithms. I've been browsing the project pages for UPX, but they are 
extremely sparse on documentation.


Markus

-- 
Markus Gutschke
3637 Fillmore Street #106
San Francisco, CA 94123-1600
+1-415-567-8449
ma...@gu...

Re: [Etherboot-developers] upx compressor/decompressor...

[Eric W B. <ebi...@ln...>]

Markus Gutschke <ma...@gu...> writes:

> Eric W Biederman wrote:
> > In it's final form the overhead for the nrv2b decompressor is just
> > 180 bytes and should handle any size of file.  The 32bit infrastructure
> > is now an advantage instead of a liability size wise.
> 
> Sweet! That's very impressive. Now, if only there was some documentation on
> these algorithms. I've been browsing the project pages for UPX, but they are
> extremely sparse on documentation.

The simplied version is now checked in to etherboot cvs.

Conceptually it is based on copying bytes.  But instead of using
a hufman tree to encode the bits, it uses an encoding based upon stop
bits.

Check out the decompressor in nrv2b.c it is only about a screenful so
it isn't to hard to comprehend.  Watch out for the GETBIT code though
how it uses stop bits instead of a count to remember how far to go is
interesting.

Then look at the unnrv2b.S the optimized assembly version, and notice
how a lot of the awkward cases in C, become straight easy to
implement in the assembly.

Eric