I vote NO on Motion P1788/M0024.02:RoundedOperations
Folks,
I vote NO on Prof Kulish's motion to require a
conforming implementation to provide explicit
hardware instructions for directed rounding
operations.
There are many reasons.
We are an arithmetic standards body not a hardware
standards body. It is not our place to dictate
how our implementers shall design their hardware.
Also, to do so would eliminate nearly all existing
hardware from any possibility of conforming to our
standard. This would severely limit acceptance of
1788 in the market.
We have already gone out of our way to provide for
the flexibility necessary to eliminate the need for
frequent changes in rounding mode. For example,
permitting representations of the form [-inf,sup]
rather than [inf,sup]. Thus, much of the performance
improvement Prof Kulish seeks can already be had on
existing hardware without new instructions.
All of that having been said, what Prof Kulish
suggests would clearly be a good idea for any
architecture that permits it. Indeed, some already
have such instructions. But it is up to the hardware
designers to decide what is best for their customers,
not us.
Perhaps someday hardware designers will include even
more useful instructions than explicit directed
rounding instructions. If 1788 is successful we may
even see explicit interval registers with explicit
interval add, subtract, et al.
But not today.
And not by our demanding it of them.
That's how I feel anyway.
Yours,
Dan