From: Martin Ling (martin@nodezero.org.uk)
Date: Thu May 04 2000 - 07:38:48 MDT
On Wed, May 03, 2000 at 11:51:46PM -0400, Michael S. Lorrey wrote:
> Matt Gingell wrote:
> >
> >
> > On the one hand, you'd think there might be situations where a system
> > emulating its own substrate could actually yield a speed increase. For
> > instance, take a chip running a instruction-level simulation of
> > itself. To elaborate on your example, let's say multiplication on this
> > chip is very inefficient: it takes longer to multiple 5 by 6 than it
> > does to do 5 adds. If I simulate multiplication by doing additions,
> > then I'd get a speed increase.
> >
> > But this is a one time optimization: If the emulator runs another
> > layer of simulation, I won't get the same increase. And I only get a
> > speed up on programs using the multiplication instruction - so I don't
> > have a faster chip, that is a chip that runs every program faster than
> > the substrate, I only have a chip than runs a subset of programs
> > faster. You always have to bottom out somewhere.
> >
> > There's an analogy here to data compression: There exists no algorithm
> > which can be guaranteed to shave a bit off any arbitrary bit string. If
> > there were, applying the algorithm enough times would compress
> > anything down to zero. All you can do is map frequently occurring
> > patterns down to short encodings at the expense of making less
> > frequent patterns more expensive to express.
>
> The problem with compression, which is why simulations cannot accurately
> reflect a real reality, is that compression loses detail. Its lossy.
> Granted there are some ways to compress data that simply a more
> efficient method of organizing information or in the example above,
> using one fast method to simulate another method that actually runs
> slower, however at some point, you've optimized organizing and
> methodology to its most concise point, anything beyond that and you have
> to destroy actual data, for example, JPG images.
There are both lossy and non-lossy compression algorithims. JPEG is a
lossy one, GIF is not. And of course ZIP isn't.... :-)
Martin
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