[SeaBIOS] Adding non standard VGA modes

[Bernhard Guillon]

Hi all,
I want to ask if it is possible to add non standard VGA modes like 800x480 
to seabios vgabios implementation. I want to be able to use it for qemu. 
After looking at the code I am puzzeled about the "random numbers" 
e.g. [1]. 
Can you hint me to any documentation or books I can read to understand 
what they are doing?

best regards,
Bernhard

1 http://code.coreboot.org/p/seabios/source/tree/master/vgasrc/vgatables.c