(j3.2006) BEQ, BNE?

[Van Snyder]

On Thu, 2013-01-31 at 08:07 -0600, Bill Long wrote:
> 
> On 1/30/13 7:53 PM, Malcolm Cohen wrote:
> >> I assume this is a theoretical question
> >
> > Sorry, but I am with Van here.
> >
> > It is so far from inconceivable that machines will have this kind of arithmetic
> > that there are machines currently being produced with this kind of arithmetic.
> >
> > We have gone to great lengths in the real, integer, and bit models in clause 13
> > to avoid gratuitous machine dependencies, even to the extent of handling radices
> > other than 2.
> 
> Parts of those lengths are in 13.3 where we make the interpretation of 
> negative integers as bit sequences processor dependent, as well as 
> pretty much everything related to bit sequences for non-binary integer 
> representations.

Don't forget 4.4.2.2p1, which says that the integer zero value is
considered to be neither negative nor positive, and that a signed zero
has the same mathematical value as an unsigned zero.  The standard
clearly contemplates platforms with two representations of zero.

> (Of course, I would have preferred to just have left BITS in the draft 
> standard, avoiding the need for any of the B** functions.  But that 
> position did not get consensus.)

You would have had my vote on BITS if you had specified a length
parameter instead of a kind parameter.

> Ultimately, it is a question of where we put our efforts.  We can go to 
> lengths to accommodate extinct (for good reason) hardware failures, or 
> focus on challenges that we can be confident will be affecting 
> scientific computing in the time scale of vendor implementations of the 
> next standard.  Among those challenges, I don't see duplicate 
> representation of integer values anywhere on the horizon.

Except, as Malcolm points out, they are being manufactured now.  I don't
have as clear a crystal ball as Bill has, but I do have colleagues who
keep close track of developments in chips with literally thousands of
tiny processor cores.  There seem to be several new entrants into this
game every year.  The last one they alerted me to is Altera (or is it
Alterra?).  Who knows how many of those have (or will have) multiple
representations of zero?