[ipxe-devel] [PATCH] Replace the nrv2b compression algorithm with lzo1x

[Joshua C.]

2012/5/6 Michael Brown <mbrown at fensystems.co.uk>:
> On Sunday 06 May 2012 17:46:33 Joshua C. wrote:
>> The UCL compression library and the nrv2b algorithm haven't been
>> actively developed since 2004. Some parts of the code are incomplete
>> and are set to not compile anyway. I decided to replace the nrv2b
>> algorithm with the lzo (especially the lzo1x_999) because it is in a
>> better shape and achieves a faster decompression speed. More info
>> here: http://www.oberhumer.com/opensource/lzo/#documentation
>>
>> The only thing that needs to  be done is to replace the nrv2b
>> decompressor with the lzo.
>
> Thanks for taking a look at this!
>
> I'm not familiar with LZO.  Do you have an estimate for the expected binary
> code size of the decompressor?  (For reference, the current decompressor is
> just 155 bytes.)  Decompression speed is irrelevant for iPXE; what matters is
> the compression ratio, and the size of the decompressor itself.
>
> Michael

I did some recompilation and came to the following results (everything
was set to stock, compilation of bin/10ec8168.lkrn):

with the nrv2b algorithm:
nrv2b-decompressor: 144 bytes
lzo1x-asm-decompressor: 398 bytes

with the lzo1x algorithm:
nrv2b-decompressor: 144 bytes
lzo1x-asm-decompressor: 395 bytes

For the testing I just replaced the unnrv2b.S and unnrv2b16.S files
with the asminit.def and lzo1x_s1.S and adjusted the libprefix.S file.
Those are the differences to the size of the lkrn image without any
compressor. I'm not sure if those figures accurately represent the
real size of the decompressors.

However I have to admit that with the lzo1x compression my lkrn was
with 3452 bytes (3455 bytes) bigger than the one with the nrv2b
algorithm. This falls in line with the documentation of lzo that the
algorithm takes approx 3-4KB. LZO has been developed as a successor to
ucl (which includes versions of the otherwise proprietary nrv
compression) with decompression speed in mind. I think maybe more
testing is needed but in my opinion the lzo1x can do an overall better
job than the ageing and incomplete nrv2b.

--Joshua