Re: [Qemu-devel] [PATCH v15 2/9] Add XBZRLE documentation

[Eric Blake]

On 07/05/2012 06:51 AM, Orit Wasserman wrote:
> Signed-off-by: Orit Wasserman <address@hidden>
> ---
>  docs/xbzrle.txt |  136 
> +++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 files changed, 136 insertions(+), 0 deletions(-)
>  create mode 100644 docs/xbzrle.txt
> 

> +
> +Example
> +old buffer:
> +1001 zeros
> +05 06 07 08 09 0a 0b 0c 0d 0e 0f 10 11 12 13 00 00 6b 00 6d
> +3074 zeros

This _still_ doesn't add up to 4096:

1001 + 20 + 3074 = 4095

> +
> +new buffer:
> +1001 zeros
> +01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f 00 00 67 00 69
> +3704 zeros

Still a transposition error.

Also, this still has the flaw that it is too weak of an example - the
only unchanged bytes happen to also be zero bytes to begin with; it
would be much nicer if the example included at least one non-zero byte
that did not change between old and new.

> +
> +encoded buffer:
> +
> +encoded length 24
> +e9 07 0f 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f 03 01 67 01 01 69
                                                         ^^
That says you have a zrun of 3 bytes, but the example only shows a zrun
of 2 bytes.

It feels like I'm pulling teeth to get a good example.  If you will just
squash in the following (hand-written) diff below, you will then have
4096 bytes in both old and new buffers, and your encoded buffer listing
a zrun of 3 will be correct, plus you will be demonstrating a non-zero
byte that remained unchanged.

@@ ???,??? @@
 Example
 old buffer:
 1001 zeros
-05 06 07 08 09 0a 0b 0c 0d 0e 0f 10 11 12 13 00 00 6b 00 6d
+05 06 07 08 09 0a 0b 0c 0d 0e 0f 10 11 12 13 68 00 00 6b 00 6d
 3074 zeros

 new buffer:
 1001 zeros
-01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f 00 00 67 00 69
-3704 zeros
+01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f 68 00 00 67 00 69
+3074 zeros

 encoded buffer:

-- 
Eric Blake   address@hidden    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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