[TUHS] Re-implementations/Clean-Rooms et al.

[Larry McVoy]

On Thu, Sep 08, 2022 at 05:50:37PM -0400, Clem Cole wrote:
> > BSD is a different beast, as they were literally replacing the AT&T source
> > code before their eyes, so there isn't much argument that can be made for
> > 4.4BSD being a "clean-room" implementation of UNIX.
> 
> It was not a clean-room as Arthur defined it.   It was rewritten over time,
> which replaced AT&T's implementation.  Which is all that was ever claimed.

And it's a false claim.  Go look at the Bell Labs bmap() and the BSD
bmap(), the last time I looked they were bit for bit identical.

I looked there because I split bmap() into bmap_read() and bmap_write()
because the read path is trivial and the write path is quite a bit more
difficult (this was all for the work srk imagined, and I did, to get
rid of the rotational delays).  So I was pretty familiar with that
code path and as of about 20 years ago, well past 4.4BSD, bmap() was
unchanged from either v7 or 32v.

The weird thing is it isn't that hard to write something that would
walk the code and find other examples.  Nobody seemed to care.