Re: AES and dynamic table generation

From: Tom St Denis (tomstdenis_at_iahu.ca)
Date: 01/12/04 

Date: Mon, 12 Jan 2004 13:25:16 GMT

"Simon G Best" <s.g.best@btopenworld.com> wrote in message
news:40029237.800@btopenworld.com...
> Tom St Denis wrote:
> > "Brian Gladman" <brg@nowhere.at.all> wrote in message
> > news:nFWKb.19364$qx2.2163603@stones.force9.net...
> >
> >>Its very easy to make dynamic tables thread safe and they do have
> >>significant advantages in some environments.
> >
> > In a portable fashion?
>
> The OP didn't limit the context of the question he asked to just
> multithreaded, portable applications.
>
> Consider a microcontroller with limited nonvolatile memory, but plenty
> of RAM. If that's going to be used in an application where the speed of
> lookup tables is required, dynamic table generation might be the only
> option!

A microcontroller with little ROM and plenty of RAM? Where do these come
from? 8051 has 256 bytes of ram [that you'd want to use] and upto 64KB of
ROM... The 6805 series is similar. RAM is hella more expensive in fielded
designs then ROM is.

The only real "benefit" of dynamic tables is I can now send you a shorter
executable. But since the program only has to be stored once [this is AES
afterall] there's no point in wasting the 10KB [or so] of RAM on tables that
could just as easily fit in ROM.

Note that for the purposes of this post you can consider ROM to also mean a
"constant array in the C language".

Tom

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