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Re: [PATCH] LZMA support in i386-pc kernel

From: Vesa Jääskeläinen
Subject: Re: [PATCH] LZMA support in i386-pc kernel
Date: Wed, 02 Jul 2008 20:50:52 +0300
User-agent: Thunderbird (Windows/20080421)

Bean wrote:

This patch add support for lzma decompression. The assembly code
lzma_decode.S is manually optimized to reduce size. The result decoder
is tiny, only 416 bytes longer than the lzo version.

Not bad.

I also include lzma encode from the LZMA SDK. grub needs to use the
ANSI-C version of encoder, which is only present in the latest 4.58
beta. I can't find ready to use shared library in most distro.
Including the encoder/decoder has advantages as well. We don't need to
worry about the host os, and lzma encoder/decoder can be used in other
place, like font compression.

We can load more complete decoder module after we can load modules and leave more optimized version in boot code.

I use lzma as default, it's still possible to use the old lzo
compression, you just need to add --enable-lzo option when running

PS, here are some information about the lzma decoder:

properties: lc = 3 lp = 0 pb = 2
memory requirement for the decoder: 15980 bytes

Can we probe for best values and then use always the best? Perhaps embed them as constants to boot code?

Result of
./grub-mkimage -o core.img biosdisk pc ext2 lvm raid

lzma version: 27,776 bytes
lzo version: 32,768 bytes

Not bad. Not bad at all.

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