Re: I wanna write an RFC

[davidk@lysator.liu.se (David Kågedal)]

David Hedbor <david@hedbor.org> writes:

> Hrvoje Niksic <hniksic@srce.hr> writes:
> 
> > David Hedbor <david@hedbor.org> writes:
> >
> > > Also all implementations of x-face are buggy.
> > 
> > I don't understand this.  All the implementations I know of are using
> > the "uncompface" code, either through the external program, or through
> > the library.  Is that code buggy, or do you claim that the
> > specification is buggy?
> 
> That code doesn't follow the specification. I don't know exactly what
> the error in that code is, but I can find out if anyone is interested.

As I understand Marcus (out mutual friend who investigated this), the
code uses arrays for some sort of prediction, but it indexes them at
least one index off, resulting in both that the predictions don't work
as expected, and that it reads memory outside the table.  This
out-of-bounds memory happens to be in another structure in the
compface code, but since everybody uses the same code, it always works
the same way.  However, if you want to write another implementation
you'll have to reimplement all the bugs.

-- 
David Kågedal        <davidk@lysator.liu.se> http://www.lysator.liu.se/~davidk/